My HF Receiver Collection

10 November 2017


Introduction

I'm something of a packrat when it comes to radio gear - easily tempted, and reluctant to move things on. I am in particular a sucker for design excellence, and like to collect items that represent the best engineering and advanced design. I'm especially interested in early high-performance solid-state receivers.

Once I'd collected more than a dozen receivers, some of them quite interesting, I realized I was on my way to making a serious collection. Most of my collection are HF receivers, but I also have some interesting transceivers, VHF receivers, and one very old broadcast radio worthy of mention.

The oldest in the collection dates from 1924, and I've examples from the 50s, and every decade since. I just wish I still had a few I passed on long ago - a Murphy B40, and a Marconi AD94, for example. But then, I'm having trouble finding space to display and operate the receivers I have! Most of the receivers are currently in operating condition.

The receivers are listed in approximate order of age, oldest first. I've some interesting documentation for some of them, and next to none for others. But for every one, I have at least basic details, and a photo. Many of the photos are taken in-situ, so may not be the best.

If you'd like to see the collection, free of charge, phone me or send me an email for an appointment. I can demonstrate most of the receivers running on-air.

The location is wheel-chair accessible

Many of the photos are larger than displayed, and if you click on the blue title under each picture, you will be able to see the image in full resolution.

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Views of my receiver collection  (1)  (2)  (3)

How YOU Can Help

I would welcome any assistance in improving and enlarging this collection. Most of these suggestions by necessity will involve volunteers from the local area, say Northland, Auckland and the Waikato, but donations of receivers to the collection, and money to help pay for restoration, are welcome from anywhere.
  • Mechanical repair. Several of the receivers (example - the Eddystone 840A) require restoration work, which is mostly of a mechanical nature. If you enjoy this type of thing, let me know, as there is plenty of scope!
  • Electrical repair. Some of the receivers are non-going, but the cause is known (example - the Drake DSR-2). Others have problems yet to be investigated (example, the RACAL RA6790/GM). Here a volunteer would find the problem, source replacement parts, fit them and test the receiver. Let me know if you are interested.
  • Documentation. If you have brochures, manuals or schematics for any of the receivers in the collection where I have specifically mentioned being short of information, please let me know.
  • Receivers for the collection. I am always looking for further receivers, especially early solid state communications receivers. I prefer receivers designed and built to a high standard, or designs which have made a significant contribution to the development path of receiver design. Do you have a receiver you would like to donate? Do you have a receiver you would like to be part of the collection, even if it needs restoration? Would you like to see your receiver in a collection, even though you still own it and wish to maintain some control over its future? Do you have suggestions? Contact me. I am prepared to collect from anywhere in the North Island.
  • Exhibition space. I live in Waiuku, which is a little off the beaten track, and I'm looking for a venue where some of the collection can be housed occasionally, and where there is easier access. Waiuku already houses an important collection of military radio equipment thanks to Ross Jowitt ZL1UND, and is of course the home of the Glenbook Vintage Railway. Any suggestions?
If you wish to help in any way, please contact me by email.

The Receivers

1a. RCA Radiola III-A (1924)

This is a very early four valve regenerative AM receiver, covering 220 - 550m (540 kHz to 1.4 MHz). It's not operational, as I don't have the appropriate valves (UX199 and UX120). The first stage is a regenerative detector, followed by an audio amplifier, and a push-pull audio output pair capable of driving a loudspeaker.

Inside, the condition is remarkable, although the rubber shock-absorbers for the valve sockets have collapsed. It was designed to run off one A cell for filaments, and a collection of 22.5 and 45V batteries for HT. The headphone/ speaker connections are live to the HT!

The receiver is mounted in a sturdy french polished wooden box with dovetailed corners, about 300 x 170 x 120 mm. The front panel is made of pressed Bakelite. I was given the receiver while working in the USA in the late 1990s.

       
The Radiola III-A (left), the original rear-panel label (centre, 1.5 x life size), and a UX199 valve (right)

Make sure you check out all the detailed photos in the list above. I recently found some reasonable replicas of the original 'tubes' (valves) as you will see here. The 'tubes' are actually 'Edison style' LED garden lights with silvered glass envelopes, and glow yellow when powered up. They look remarkably realistic!

1b. RCA Radiola III (1924)

This is the smaller brother of the Radiola IIIA. The first two stages are virtually the same, a regenerative detector, followed by a transformer coupled headphone amplifier.

The interior looks like new, and the exterior is also in very good condition, despite surviving for 93 years. The receiver is mounted in a sturdy french polished wooden box, about 200 x 165 x 120 mm. The front panel is made of pressed Bakelite. I was given the receiver in 2017 by a friend, Doug Lux WB6VAC. It came with the original manual and CAMCO 'Cannon-ball Junior' headphones.

At some point in the last 50 years, the tubes have been replaced with 'pencil tubes', a CK505AX and a CK512AX. I have yet to find out if it works. The radio operates from 22.5 V (detector) 45 V (audio stage), 1.5 V filaments and a separate 1.5 V bias battery. The power lead looks new, and is braided with individual metal identification tags on each lead. The leads end in automotive bullet connectors.

   
The Radiola III top view and oblique view

Looking at the picture on the left, the 'Amplification' control adjusts the reaction of the detector stage, using a variometer within the detector coil. The 'Station Selector' tunes in the stations, using another variometer within the antenna coil. The knob top left adjusts the filament current (large rheostat), and acts as the On-Off switch.

The terminals top right are the antenna connections (top) and the band 'switch' with link below. There are three operating ranges, 535 - 950 kHz, 625 - 1200 kHz and 830 - 1500 kHz.

In the interior views (links below), you can see the large coils and variometers, and the other details described above. In 1924, this radio cost $24.50, or about six week's wages, yet despite this, the radio was hugely popular. For $24.50 today (pocket change), you could buy two AM/FM/Short Wave synthesised radios like this one!

2. Wavemeter Collection (1941 - 1963)

I've lumped these four units together here for convenience (and although interesting, they aren't really receivers). In the picture below, the one at the top left is a US Navy LM-10 crystal calibrator/wavemeter, dating from about 1943, manufactured by Bendix Radio. It is in reasonably original condition, and still operational. It still has the original calibration booklet (underneath it). As well as operating as a heterodyne wave meter (there was a 1 MHz reference crystal and a calibrated VFO), the LM-10 could AM modulate its oscillator at 400 Hz for use with AM receivers. The calibration books were individually calibrated and printed.

On the bottom left is a similar vintage (1942) BC-221-AF, built by Bendix Radio for the US Army. It has lost the original case and is not operational, but I do have the original calibration booklet and the schematic plate from the case. These units were battery operated and of very similar construction to the LM-10, although they lacked the modulated oscillator capability of the LM-10.

The RCA TE-149 wavemeter (bottom right) was made in Canada by the RCA Victor Company in 1941, and operated in a similar way to the LM-10 and BC-221. Although the case is complete, the internal circuit ry has been 'got at' in an attempt to use solid state devices, and it isn't working. The TE-149 has an unusual tuning mechanism with a spiral disc which operates the tuning pointer, which points to a spiral scale on the visible side of the disc. The unit was also battery operated, but was not capable of the frequency accuracy of the LM-10 or BC-221, as it lacked interpolation capability and therefore had no calibration book.

The final unit (blue box top right) is a simple passive wavemeter dating from 1963, and built for the Navy. It covers 0.1 to 35 MHz. The unit has no detector or indicating device - it's just a tuned circuit. It's title (believe it or not) is '6625-99-972-6347 Detector Radio Frequency'.

 
The four wavemeters (left)                     The Bendix LM-10 (right)

3. Belmont Mantel Radio (1940)

By the 1940s, superheterodyne design was common, making radios more stable and much easier to tune.This radio was (I understand from family lore) built from a kit by my father during the Second World War. However the case and chassis are clearly commercial, and the brand name on the dial plate 'Belmont' belongs to a Chicago firm. The radio is 230V operated, and clearly has some local components (such as the Rola EM speaker). It's my guess that the radio was actually assembled in New Zealand, and (possibly) was available at the time as a semi-kit. The valves are Octal types. It is a conventional four-valve plus rectifier design with a wooden case embellished with marquetry veneer. The veneer continues in a smooth radius around the sides, and it's my guess that the veneer was laid up and moulded in a jig.

   
Belmont mantel radio (left), and a rear view (right)

4. Ultimate (Radio 1936 Ltd) Mantel Radio (1950)

This radio represents the typical 'mantel radio' of the 1940 - 1960 period. It uses the (then) new Loctal type valves, which were more compact than the earlier types, and had a secure lock-in base which made them useful in car radios subject to vibration. The Ultimate brand was manufactured in New Zealand for many years by Radio (1936) Limited, until they were eventually absorbed by Pye. Radio 1936 Ltd manufactured many of their own parts.

This radio represents economy of design: the valves are a mixer/oscillator, an IF amplifier and a single high gain audio output tube which incorporates the detector diode, plus a rectifier tube. The last mentioned three valves can be seen left to right in the rear view picture. The mixer/oscillator is hidden behind the left-most can. The two cans are of course the two IF double-tuned circuits. The case is moulded from casein, an early plastic material. The loudspeaker was made in Australia by Rola. On the rear panel, in addition to the model and serial number label, you can see the remnants of the 'ARTS&P' transfer, which states that the radio was manufactured subject to a range of licences for private use. 'ARTS&P' stood for 'Australian Radio Technical Services & Patents Co. Limited', who were patent attorneys and representatives at the time. Many of the developments in radio receiver design were then still subject to patent restrictions. (The patents for radio valves and the superheterodyne technique eventually expired in the mid 1960s).

   
Ultimate mantel radio (left), and a rear view (right)

My grandmother bought this radio new, and it was left to me when she died in 1953. It was my first radio receiver, and I used it to listen to 'DX' broadcast stations from Australia and beyond.

5. Eddystone 680X (1951)

The next receiver is a true general coverage HF receiver. It covers 480 kHz to 30 MHz in five bands, and sports the now famous Eddystone 'slide rule' dial. The receiver has 15 valves, mostly miniature, including a voltage regulator for the oscillators. It is interesting to compare this Eddystone with the next one, as although they have similar appearance, this one is much more complex. It has two RF stages, two IF stages, and push-pull audio output.

The receiver is too early to have a product detector, so SSB reception is poor, although CW is adequate. The receiver has adjustable IF bandwidth, with four settings, as well as a single-crystal filter in a phasing network. The power supply tends to generate noise, so it needs to be used with a remote antenna and shielded antenna lead.

The receiver covers the MF and HF range in five bands: 480 - 1110 kHz, 1.1 to 2.5 MHz, 2.5 to 5.7 MHz, 5.3 to 12.5 MHz and 12.3 to 30 MHz. It uses largely B7G minuature valves. The exceptions are the rectifier and voltage regulator tubes. Plenty of audio is provided by the push-pull audio output stage.

The 680X is single-conversion, with an IF of 450 kHz, and two RF stages to give improved RF selectivity to avoid image responses. Performance is adequate, although it is a bit flat above 15 MHz. Not small, the receiver is 450 mm wide and 220mm high, 300mm deep, and weighs over 21 kg. The front panel is diecast, and the case is finished in hammerglaze grey. It took me a while to find the headphone socket - it's on the left side!


The Eddystone 680X

6. Eddystone 840A (1954)

The external appearance of the 840A is quite similar to the 680X, but inside it is a very different beast. Built for a different market (as a 'cabin radio' for use on ships, and as a domestic radio in 'The Colonies'), and in a different price range, the 840A has only one RF stage, and only one IF stage. The most important difference is that it is an AC/DC set, so will operate from 110V, 200 or 230V, AC or DC. DC supply used to be common on ships and for home lighting plants in remote places. There are only seven valves, and no 'S' meter on the panel. The valves are from the 'Noval' 100mA filament U series.

My example has been 'got at' to some extent. The ballast resistor is missing, so it is committed to run from 110V AC; there are various internal 'improvements', plus an 'S' meter had been fitted through a hole in the top of the cover. The BFO knob to the right of the Tuning knob is not the original one.

The panel layout is different to the earlier receiver, and having no crystal filter, the corresponding knob is replaced with a Tone control. While the main tuning dial is the usual large slide-rule affair, there are only four bands: 480 - 1400 kHz, 1.4 to 3.8 MHz, 3.7 to 10.6 MHz, and 10.5 to 30 MHz. In this receiver, Amateur and Broadcast bands are marked on the dial in blue and red respectively. The brochure comments that the receiver covers the 500 kHz marine frequency.

The receiver has the same width and height as the 680X (450 mm x 220 mm) but is only 230 mm deep. It's considerably lighter than the 680X. I can't comment on the performance yet, as this radio has yet to be restored.


The Eddystone 840A (unrestored)

7. Collins 51J-4 (1955)

This is arguably the best of my valve receivers. Even today the performance is impressive. It is very stable, as it uses the famous Collins PTO (permeability tuned oscillator). The receiver covers 540 kHz to 30.5 MHz in 30 x 1 MHz bands. Band change is achieved using switched slug-tuned coils. The coils are ganged and track with the tuning knob, and the dial scales are on a drum which rotates with the band change knob. There are 16 miniature valves.

The first IF is tunable in two ranges (0.5 to 3.5 MHz), and is followed by a second IF at 500 kHz, which has both a phasing crystal filter and a useful range of mechanical filters. The receiver is superbly stable, has good sensitivity, excellent calibration, and is a great AM/CW receiver. With no product detector, SSB performance is modest. Sensitivity at 30 MHz is very good.

I used to own a 51J-3, and was able to upgrade to this even better (one owner) receiver, which is in virtually original condition. Unlike the one in the photo below, mine includes a black desk-top rack case. Its history is interesting - it was imported for propagation research by the Auckland University Radio Research Department in 1955, and remained in their ownership, little used, until I took possession in about 1999.


The Collins 51J-4

8. Collins 75S-1 (1958)

This receiver was designed for Amateur use, to transceive with the companion 32S-1 or KWS-1, and covers the ham bands and some other optional parts of the HF spectrum in 14 x 200 kHz segments. It uses 12 valves.

The receiver covers the range 3.4 to 30 MHz, and uses a crystal controlled first conversion. Coverage is not continuous. Some of the bands in my receiver have been changed for short wave reception, and when I collected the receiver (at no cost) it was not working and most of the case screws were missing. It's also a 110V receiver, so not the most convenient. This is the oldest receiver I have which uses a product detector, and SSB reception is very good.

The 75S-1 has a tunable IF of about 3 - 3.2 MHz, following a preselector and band converter. The second IF is 455 kHz. It has a single SSB mechanical filter, switcheable BFO crystals for USB/LSB, with LC filters for AM. The vernier tuning dial is rather nice, but has rather slow tuning and limited range per band. Reception is adequate, even on 10m. The preselector is annoying as the planetary drive slips at times.


The Collins 75S-1

9. Drake 2B (1961)

When it was first released, the Drake 2B caused quite a stir, and quickly became very popular. The performance is excellent, and the stability is remarkable for a valve receiver. Great care went into the VFO design to provide maximum stability. This is my 'newest' valve receiver, and the oldest of my three Drake receivers. The receiver (which cost me $50) required only minor repair and an exterior clean-up. It gave the appearance of having been home to mice at some point, but despite this, the interior and copper-plated chassis are clean, and it operates really well. I also have the Heathkit after-market crystal calibrator fitted, and own a Codar RQ10 Q Multiplier designed for use with the 2B.

The 2B has a slide-rule dial, but isn't as good as that in the old Eddystones. It feels light and has some backlash in the pointer (but not the tuning). There are 10 valves, and the arrangement is triple conversion, with a crystal-switched first conversion, a tunable 3500 - 4100 kHz first IF, 455 kHz second IF and 50 kHz third IF. The receiver has passband tuning in the third IF, which is very effective, and three bandwidths, 0.5, 2.1 and 3.6 kHz. SSB reception is excellent, and stability is unbelievably good for a modestly priced valve receiver of that vintage.

The 2B is nominally ham-bands only, with 600 kHz range on each of 12 bands between 3.5 and 30 MHz. The receiver uses a preselector, and by judicious fiddling, you can achieve reverse tuning on some additional frequency ranges. My 2B is 110V operated. The receiver is quite small - dimensions are 300 x 220 x 180 mm.


The Drake 2B

10. Plessey PR152 (1962)

Without question the oldest of my solid-state receivers, the Plessey PR152 is also one I know very little about. It uses PNP Germanium transistors, OC171 in the front end, and many GET535 devices elsewhere. From what I understand, it is double conversion, with a 1.6 MHz first IF and 480 kHz second IF. There is a 1100 kHz crystal oscillator. The second IF coils are double-tuned, giving a slightly double-humped passband, which I have measured to be 7.5 kHz wide at the 3dB points, and about 13 kHz at 30dB down.

Coverage is 550 kHz to 30 MHz in six bands. There's no preselector, but the antenna trim is quite sharp, which combined with the use of Litz-wound coils give the impression of good front-end selectivity. While more a 'short wave radio' rather than a communications receiver, performance is fairly good, even up at 30 MHz. Stability and AM audio are good. There's no product detector (which is sad, as SSB had been around for some time in 1962), and although CW reception is reasonable, SSB is pretty tricky. You don't really have single-signal reception because of the wide IF, and the tuning rate is a bit fast, so tuning in SSB is best done with the BFO control. There is just one IF bandwidth, but there is a really sharp audio filter for CW reception, unusual for a 'short wave radio'. It is centred on 1 kHz and is about 100 Hz wide at the 3dB points, 600 Hz at -30dB.

Given the age of the radio, and that it uses Germanium transistors, the sensitivity is remarkable. I measured about 3uV for 10dB SNR on all bands, and slightly better toward the top end of each band. That's very good considering the broad IF.

The assembly consists of a conventional chassis with a main circuit board beneath (IF, filter and audio), while the tuner and bandswitch assembly is off to one side, incorporating other small circuit boards, with the tuning gang next to it. The battery eliminator sits on the chassis behind the tuning mechanism. Almost every wire in the radio is PINK, making tracing circuitry a challenge! The front panel is a simple flat Aluminium anodized plate with silk-screened black text, over a steel front panel. The case is a large machined Aluminium casting. Construction is very sturdy.

The most remarkable feature of this receiver is the tuning mechanism. It features a 70mm film-strip dial (equivalent to six metres long!), and a 70mm diameter tuning drum which is driven by direct and planetary drive knurled wheels to the right of the drum. The drum drives the tuning capacitor via a worm-drive with anti-backlash gears. The tuning mechanism has a sturdy cast Aluminium frame, with bronze bearing inserts, and tuning is smooth and easy, with no backlash. The bandspread impressive. There's a further concentric wheel to the left of the drum which moves the dial pointer to provide localized calibration, although it seldom needs tweaking as the calibration is good. (The set has a 1 MHz and 200 kHz crystal calibrator).

Nominally a 9V battery operated set, my PR152 is fitted with a 230V 'battery eliminator', which makes life convenient. Because it is designed for battery operation, power consumption is low (about 50mA at 9V, peaking at 100 mA with full audio) and there are no panel, meter, or tuning dial lights. Audio quality is excellent, and there is a good-sized speaker in the left side.

Believe me, you'll find nothing on the internet about this receiver, apart from a press release in Wireless World Feb 1963, which says:

"Plessey Communications receiver type PR152 is a compact all-transistor model covering the m.f. band (550-1500 kc/s) and the h.f. band (1.65-30 Mc/s) with a film-scale tuning system giving a total effective scale length of 18ft."

As you'll see from the photographs, this rare receiver is in remarkably fine condition for its age. Everything is original, right down to the unusual bathtub-shaped knobs. The rear RF connector is a UHF (SO239) type.

   
The Plessey PR152 (left),           rear view with tuning mechanism (right)

11. Eddystone EC10 Mk 1 (1968)

This is Eddystone's first solid state receiver. It's really interesting to compare this receiver with the slightly older Plessey PR152 shown immediately above. It's very obvious that the Eddystone has good looks, and has a classic Eddystone appearance. It is ergonomically well designed as well. The Plessey is in contrast fairly utilitarian, and while the film-strip dial has far better accuracy and band-spread than the Eddystone, it is not as easy to tune around with vertical edge-tuned knobs. The other big difference is in performance: the Eddystone is fairly modest, lets say, while the Plessey is quite impressive for its age.

The EC10 is a single conversion short wave listener's receiver with a 465 kHz IF, and a fixed IF bandwidth, suitable for AM. It includes a BFO, although performance on SSB is quite poor. It's not so much actually resolving SSB, but that the receiver pulls quite badly as a result of AGC action. It is best with the AGC off, controlling the signal with the RF Gain, and then SSB is reasonably intelligible.

The receiver covers 550 kHz to 30 MHz, continuously in five bands. Bandspread is reasonable up to about 10 MHz, although the calibration accuracy is modest. The level of audio distortion is not up to modern standards, and probably comes from the diode detector.

The EC10 is well constructed, with the RF board at the bottom, and the IF/Audio board inverted at the top (see picture links below). Access is quite good, as the IF board can be rotated and secured, giving access to both sides and to the top of the RF board. The OC170 RF amplifier is arranged in common base, and there are two double-tuned IF amplifiers with AGC. While there is a 465 kHz trap at the antenna, IF breakthough can be a problem, and above 8 MHz, image rejection is modest at best. There is an effective 1 kHz audio filter for CW reception.

My EC10 is fitted with the 'battery eliminator', which screws into the back panel. The wiring is rather lethal - you would not want to take the mains supply off or remove the folded steel case with power applied, as the AC connector terminals are then exposed. Power consumption is quite low, about 50 mA, which doubles when you activate the panel lights. The lamps are only on while you hold down the button, making the dial markings adequately visible in the dark.

The dial is similar to those of earlier Eddystone receivers, a large 'slide rule' type glass dial with very clear graduations, the pointer and tuning gang driven by a dial cord. There is no slack or backlash in the tuning, so operation is a pleasant experience. There is a 0 - 500 logging scale, and a fine logging scale above the weighted tuning knob, which allows you to interpolate the reading. The logging scale is useful because the dial calibration on most bands is fairly vague! Another point of difference with the Plessey, which has impressive dial accuracy and resolution.

The EC10 Mk1 version has no 'S' meter and no fine tune control. The Mk2 version has both, with the fine tune control replacing the headphone socket, which moves to the rear. Both lack an antenna fine tune, a calibrator (which I suggest would be essential), and neither have a means to measure the battery (the Plessey has all these).

My EC10 example goes very well, is really clean inside and out, and has few scratches on the case. No restoration has been required, although a realignment would probably be beneficial. I have added a short lead with a BNC connector to suppliment the horrible antenna connectors supplied. These aren't standard banana socket sized, and work best with a stripped wire end and a match to jam it in! Both low impedance and high (short whip) inputs are offered.

The receiver weighs about 6.5 kg (much lighter than the die-cast Plessey PR152), and is quite a bit smaller than the older (valve) model Eddystones, just 320 mm long, 162 mm high and 200 mm deep.


The Eddystone EC10 Mk 1

12. Norlin SR-219 (1965?)

This is a surveillance receiver from the mid 1960s. I don't know much about it, except the IF is 21.4 MHz, and it uses plug-in heads to provide coverage from 3 MHz to 7 GHz. There were several variants with different IF bandwidths. I have two heads, covering 30 to 100 MHz (SH-201P-1) and 90 to 300 MHz (SH-202P-1), and I have borrowed and checked it with other tuners. The receiver operates FM, AM, CW and PAM. It has nice tuning and signal strength meters. A pretty receiver, with no speaker output, only headphones and a rear line connection.

Reception of FM broadcast is fairly good, and that of Amateur and commercial NBFM transmissions is adequate, but lack of squelch is a problem.

These two lowest-frequency tuner heads have an amazing planar spiral variable inductor mechanism in the ganged tuning, and all versions have a rear-lit film-strip dial and beautiful anti-backlash gearing. The design and construction of this receiver is of the highest quality. It has plug-in boards with gold-plated connections. The larger SR-209 receiver uses two of the same plug-ins, and has is a 'panadaptor' option.


The Norlin SR-219 with 90 - 300 MHz plugin

13. Redifon R499 (1969)

This receiver is a solid-state single-conversion fixed-frequency type intended for commercial installations. It was manufactured between 1969 and 1972, was widely used for marine radio applications, and is rack mounted and configured for remote control. It will operate AM, SSB, DSB, CW, or ISB, depending on the options fitted. It has a maximum of 10 channels, on MF or HF. 1ppm stability is provided by a crystal oven. Separate crystals and front end filters are required for each channel.

Frequency coverage is from 1.5 to 30 MHz, but with special MF filters can also operate from 225 to 525 kHz. The IF frequency is nominally 1.4 MHz. There is a fine tune control with an approximate range of 100 Hz. The receiver will operate from 100-125V, 200-250V AC or 24V DC, and weighs 10 kg.

My R499 is not operating, as it lacks the front-end filters and crystals. Since these were plug-in items, toward the end of the useful life of these receivers, it appears that parts were robbed from some receivers to keep other receivers going.

These receivers had a great reputation for reliability and bullet-proof performance.


The fixed-channel Redifon R499.

14. Harris RF-505A (1971)

Designed as a very high quality general purpose receiver for commercial and military applications, the Harris RF-505A (NATO R.5075/GRR) is a dual conversion receiver well suited to monitoring applications. They were used by the NZ military (mine came from the Air Force) and by the NZ Post Office as link receivers around the Pacific. I previously owned this radio around 2003 - 2008, and it returned to the collection in 2014.

The earliest example I have of a fully synthesized radio, the RF-505A is in fully working order, and also the oldest receiver in the collection with a VHF first IF.

The RF-505A is good looking, well laid out and simple to operate. It is completely 'knob tuned' (a row of decade switches) in 100 Hz steps, so needs no display. There is an interpolating oscillator available for continuous tuning between switched steps, achieved by pulling out the 1 kHz knob to activate it, then rotating the same knob to control it. The interpolation range is ± 5 kHz. All other oscillators in the receiver are referred to a very high performance ±1 in 108 5 MHz OCXO reference.

The frequency range is specified as 1.6 to 30 MHz (which is the range of the preselector), but with the preselector off, the receiver will operate down to below 100 kHz with reduced gain (sensitivity is 2 uV at 100 kHz). The first IF is 156 MHz, the second 500 kHz, using Collins mechanical filters. The first mixer is a diode ring mixer, and there is no RF amplifier apart from a 2N5179 in the optional preselector. Despite this the receiver achieves a sensitivity of 0.25 uV. The second mixer is a dual gate FET. The receiver dynamic range is more than 125 dB.

The receiver is capable of ISB operation, so has two independent IF amplifiers, detectors and audio stages. There are USB and LSB mechanical filters, one in each of the IFs, while one IF also has a 10kHz AM filter, the other a 500 Hz CW filter (mine is missing this option). While there is only one speaker amplifier, selectable between IF channels, there are two independent line-level audio outputs and two internally lit 'S' meters!

My receiver recently had a major power supply failure, precipitated by a short in the Bulova 5 MHz crystal oven. I replaced the oven with an ERC 5 MHz oven of similar vintage (from a Transit satellite navigation unit), and the receiver is back in daily operation, with stability and accuracy to die for. The receiver has a rather nice rack cabinet, not shown in the photograph.


The knob-tuned Harris RF-505A.

15. Drake DSR-2 (1974)

This good looking receiver could have been one of the most expensive receivers in my collection. It reportedly sold new for about US$3000, and was described at the time as a laboratory grade receiver, although it looks more like something you'd use with the lounge stereo! It operates from 10 kHz to 30 MHz, although the preselector only operates between 500 kHz and 10 MHz. The receiver operates USB, LSB, CW, RTTY, FM and ISB, with a separate switch to select the detector and turn the BFO on and off.

This is my second-oldest synthesized radio, and tunes in 100 kHz steps with VFO interpolation in 100 kHz bands. The three knobs in the upper centre select synthesizer 10s of MHz, MHz and 100s of kHz. These switch shafts pass through the circuit boards, stacked one behind the other, and so select the front-end tuned circuits as well as the synthesizer settings.

The receiver has a frequency counter and direct readout of frequency to 100 Hz resolution using Nixie tubes. The receiver is reasonably stable, and has excellent sensitivity. It also has a very good IF noise blanker. There are three LC filter bandwidths and mechanical filters for USB and LSB, with separate IF amplifiers allowing ISB operation.

The receiver first mixer converts to 25 - 35 MHz or 15 - 25 MHz, depending on the range, and then the second mixer to 5 MHz, then finally the third mixer to 50 kHz, using dual-gate FET mixers.

The receiver is one-owner, and looks new. Unfortunately this receiver has a fault in the synthesizer, but I have a second DSR-2 in working condition but more battered, and I intend to make one good receiver from the two.


The Drake DSR-2 Receiver

16. Wandel & Goltermann SPM-12 (1974)

I own several Selective Level Meters, and while not exactly Communications Receivers, they are none-the-less useful for this purpose, and of course give accurate signal strength measurements. The representative example here, the SMP-12, has digital locking and a 10 Hz resolution LED digital display. It covers 0.2 kHz (yes, 200 Hz!) to 6 MHz, in just one range. The tuning dial operates a VCO using a multi-turn potentiometer with an optional (pull on the knob) planetary reduction drive. The receiver also has a wideband mode. I also have the companion PS-12 generator, and the two track together. I also have the SPM-60/PS-60 pair, which are similar, but cover to 18 MHz.

The receiver has sensitivity rarely matched by other receivers, -130 dBm, and selectable filters, 1.74 kHz, 500 Hz and 25 Hz. It has no AM mode as such, but offers USB and LSB operation, with the choice of 1 kHz or 2 kHz BFO offset. The display reads the received carrier frequency when the audio pitch is 1 kHz or 2 kHz respectively.

The first IF is 8 MHz, the second at 10 kHz, and the filters are Gaussian shaped LC types. The large level meter has 2 dB and 20 dB scales, and the unit has a front-end stepped attenuator in 15 x 10 dB steps. The front-end arrangement allows for selectable input impedance and balanced or unbalanced operation. There is no audio gain control, as all control is via the stepped attenuator.

The SPM-12 is one of the very best receivers for LF and low MF use. It will receive the Russian Alpha stations at 14 kHz easily when used with an active antenna. (This is in New Zealand - range at least 15,000 km). There is no speaker-level audio amplifier, but the line-level audio output is handily on the front panel. Stability of both frequency and level is excellent. The SPM-12 is rack mountable, can be battery operated, and weighs an impressive 17 kg.


The W&G SPM-12 Selective Level Meter

17. AWA Teleradio ONE (mid 1960s)

This unit was designed and made in New Zealand. It was manufactured by AWA in their Adelaide Road factory (Wellington). It is an early solid-state radio designed for NZ Search and Rescue, and transmits and receives AM. Many of these sets were also purchased by the Mountain Radio Service. It operates on two HF channels, 5680 kHz and 4922 kHz. The unit has an IF of 455 kHz, and uses ceramic filters. The crystals fitted confirm this, and that the channels were for simplex use.

In 1974, the NZ Post Office ruled that only SSB radios could now be manufactured for use on HF in New Zealand, and existing AM radios were to be phased out by 1980. It was replaced by the SSB model TR105 (late 1970s), popularly called the 'butter box' (it was also yellow). I understand that Vern Lill ZL2TMI was closely involved with the design of the Teleradio One. He was also involved in setting up the Mountain Radio Service. Vern was also the designer of the 'Wellington Walkie' VHF hand-held radio. It had one feature in common with the Teleradio One - it used a telephone earpiece as the speaker/microphone.

   
The AWA Teleradio One (left),               The cradle with antenna wound on it (right). Note the balanced feedline and phenolic fittings. The fibreboard winder is probably not original.

The transceiver (without batteries) weighs just 882g, and is 185 mm long, 100mm wide and 110 mm deep. The front-panel dynamic microphone also acts as a speaker. The unit operates from eight AA cells, which mount inside a waterproof hatch on the front. The contruction is moderately waterproof, with a rubber gasket between the front and the case, which has instructions for use printed on it. It also has a Kiwi 'New Zealand Made' logo on the side, which is puzzling, as my research shows that this trademark dates from 1986. It may be that there was informal use much earlier.


Inside view of the AWA Teleradio One. Note the battery compartment in the case.

The two left-most boards in the above picture carry the channel crystals and tuning components. The next two boards are the receiver RF and IF, then the transmitter, modulator, and audio section.

The transmitter ran about 1 Watt. The antenna feed cable is a balanced pair, about 3.5m long. The outward ends of the antenna wires are terminated in braided nylon cord, with no formal insulators. Its previous owner was the Thames Valley Civil Defence Organization.

18. Yaesu FRG-7000 (1978)

This is my only Wadley Loop receiver. It's a bit battered, but runs OK. I keep it in the garage to monitor test transmissions. A successor to the notorious FRG-7 'frog', the 7000 is a typical 'short wave' receiver, with clock, timer and recorder control features. The receiver covers 250 kHz to 30 MHz in 30 selectable band segments. The band selector isn't a bandswitch as such, rather it selects the necessary reference harmonic for the required band. There is a band-switched preselector. The frequency display is LED, to 1 kHz resolution, while tuning is continuous.

The first IF is tunable 54 - 55 MHz, using a Wadley Loop scheme. The second IF is tunable 2 - 3 MHz, tuned by the VFO. The third IF is 455 kHz. The frequency counter measures the first and second local oscillators to calculate the operating frequency display. The FRG-7000 operates AM, USB, LSB, CW and FM. The bandwidth is 3kHz (SSB/CW) or 6 kHz (AM). There are 50 Ohm and random wire (0.25 - 1.6 MHz) antenna options. The receiver looks impressive, but is a pig to use, and stability is modest. Definitely not for beginners, as getting the band selection and preselector correct are both a bit tricky.

The receiver weighs 7 kg and is 360 mm wide, 125 mm high and 295 mm deep. It has a flimsy plastic case and solid plastic front panel.


The Yaesu FRG-7000 Receiver

19. RACAL RA6790/GM (1979)

Designed as a professional monitoring receiver, the RA6790/GM is one of the best, even today. All oscillators are referred to a single oven-controlled reference, or an external 1 MHz reference source can be used. Not small, the receiver is rack-width, 450 mm deep, and weighs 13.5 kg. The receiver nominally covers 500 kHz to 30 MHz, although it will operate quite well down to 10 kHz with appropriate firmware, although there are no bandpass filters below 500 kHz in this model.

The receiver display is via two LCD units, and resolution is to 1 Hz (the synthesizer also has 1 Hz steps resolution). There are two membrane-type keypads, which have remained reliable.

The first IF is 40.455 MHz, and the second IF 455 kHz. The first mixer uses double-balanced monolithic junction FETs, and there is no RF amp. Quite a range of filters, crystal and mechanical, are available, and five additional filters can be fitted at any one time. The receiver measures its own filters on start-up and so knows what is fitted. Optional filters range from 300 Hz to 20 kHz bandwidth, and are symmetrical. The USB and LSB filters are fixed (not replacable) asymmetrical crystal filters. My receiver does not have the ISB option.

This is the oldest micro-controller operated receiver in my collection, and unfortunately at present it has an obscure controller fault.


The RACAL RA6790/GM receiver

20. Eddystone 40A (1979)

This is primarily a Noise Measuring Receiver. While it has AGC as an option, its not a comfortable receiver to listen to, as it has a very small speaker, is easily overloaded, and has only a wide filter designed for standardized CISPR noise measurement. The receiver covers 130 kHz to 32 MHz in eight bands, with a gap around the IF frequency. It uses a slide-rule dial, with scales that rotate as the band switch is changed. A single conversion design, the IF is 1.75 MHz. The bandwidth is 9 kHz using a Gaussian filter which meets CISPR requirements. The detector time-constants and meter operation are also to CISPR requirements. There is even a BFO, although it is of limited use. Tuning is via a dial cord, and is smooth but rather slow. It takes several minutes to tune from one end of each band to the other.

The 40A operates from an internal 9V battery pack (which I don't have), external 9V via a rear-panel socket, or the optional 230V battery eliminator (which I have). It has lighting behind the dial and the meter, which can be operated from a front panel push-and-hold switch.

Intended for noise and interference measurement, the receiver has a remarkably flexible range of input options. It will operate from external whip or wire antennae, from a front-panel BNC input or from internal 'loop' (ferrite rod) antennae, one for each band, which tune with the main tuning. Because the case is fibreglass, these internal antennae are very effective, and also quite directive, so useful for direction finding. The receiver includes a pulse noise source which is used to calibrate the receiver gain at the operating frequency, since in this type of receiver, gain is not flat over the frequency range or between bands. It will measure noise or carrier level to within 1dB, using stepped 1dB and 10dB rotary attenuators at the front end.

My 40A receiver is missing the metal front trim, the carrying handle and the cover, but it works just fine, and is highly useful for locating interference and making field measurements. I have made it a rear blanking panel (to cover the battery pack/eliminator hole, and supply one of the rear feet which is normally on the power pack!), and a DC power cable for use with a 7AH 12V gel-cell battery.

The receiver is 'luggable': it weighs 10kg and is 385 mm wide, 161 mm high and 358 mm deep. It is a fine receiver, a pleasure to use, ruggedly built and well designed. Unfortunately the fibreglass case has not well survived 35 years of field use.


The Eddystone 40A Noise Measuring Set

21. Sony ICF-2001 FM/AM PLL Synthesized Receiver (1980)

The title is that given by Sony in their user manual. As far as I am able to discover, this was the first ever portable dual conversion consumer radio to offer direct entry and PLL synthesis. Other direct-entry receivers at the time were desk-top models, not battery operated.

There are a number of interesting features to the ICF-2001. It tunes in just two ranges, 150 kHz to 29.999 MHz in 1 kHz steps, and 76 to 108 MHz in 100 kHz steps. There's no 'tuning knob', although the receiver can be stepped at two speeds, although the receiver mutes and makes noises as it steps.

This is a solid and sizable portable radio (310 x 171 x 56 mm), which runs (thirstily) off three D cells or an external 4.5V supply. It draws 190 mA on FM and 225 mA on AM, so the batteries last just 10 hours. There are six user frequency memories. Two AA cells keep the micro and memories alive.

The panel is well laid out, and the receiver is very easy to use, but best if laid flat or tilted using the rear hinged stand. There is a huge (1200 mm) telescopic whip which works on all bands, a ferrite rod which operates up to about 2 MHz, and 75 Ohm external input terminals which can be used over the whole reception range. If you use the receiver on a desk, flat or tilted, the antenna base needs to be pulled out slightly and rotated forward to allow the antenna to point vertically. The receiver has a plastic shoulder strap, but you'd not want to operate it hanging from your shoulder with the antenna extended!

The design is single conversion on VHF, with a 10.7 MHz IF with two ceramic filters. On MF/HF the design is dual conversion, with a 66 MHz first IF and PLL synthesised first local oscillator. The first mixer uses balanced FETs. The second conversion is to 10.7 MHz, using a VCXO which is fixed except in SSB where it acts as Clarifier. There are double-tuned coils and further ceramic filters in the MF/HF IF. The BFO is fixed at 10.7 MHz and a product detector is used for SSB/CW. This arrangement works because the second IF is relatively broad.

There is some anecdotal evidence that John Lennon owned one of these receivers, and there is a photo I've seen showing him in a studio with an ICF-2001.

   
The Sony ICF-2001 Receiver (left)                 Detail of the receiver controls (right)

22. Rohde & Schwarz ESM-500A VHF Receiver (1981)

This beautiful rack-mount surveillance receiver covers 20 - 1000 MHz (the A version), and is accompanied by the EZP Panoramic Adaptor. There is also a small panoramic display built into the receiver. The ESM-500A and EZP can be remote controlled via IEE-488 or RS232, and set to a resolution of 10 Hz. There is an oven-controlled reference providing 1 x 10-8 accuracy. There are two synthesisers, providing for double conversion. The first IF is 310 MHz or 810 MHz, and the second IF is 10.7 MHz. The receiver weighs 18 kg, and is rack mounted.

Unfortunately my Rohde & Schwarz ESM-500A VHF Receiver is not operational, although the EZP Panoramic Adaptor works. I have the manuals.


The Rohde & Schwarz ESM-500A Receiver


The Rohde & Schwarz ESM-500A Receiver and EZP Panoramic Adaptor

23. Watkins-Johnson WJ-8718A/MFP HF Receiver (1982)

Not the prettiest monitoring receiver, this is however a top-of-the-line professional unit with excellent performance. It's not small - rack mounted, and 500 mm deep! It weighs nearly 16 kg. The front panel is clear enough, with large cream buttons, some with LED indicators, but not laid out very sensibly. Those large buttons take up most of the panel space, but at least they are decent reliable switches. The meter top left is calibrated and can indicate audio line level or signal strength.

The receiver operates AM//FM/USB/LSB/ISB and two CW modes, with variable and fixed BFO. All oscillators are synthesised from a common 1 MHz high stability OCXO, or can be externally locked. It operates from 5 kHz to 30 MHz, and has a step resolution of 10 Hz. The yellow LED frequency display is excellent, and there are similar auxiliary displays for memories and BFO offset.

The receiver has high dynamic range performance with 10 sub-octave preselector filters, and several other options fitted, including 455 kHz IF output, IEE488 remote control, carrier operated relay, and of course it is the microprocessor- controlled version.

The receiver uses a first IF of about 42 MHz, second IF 10.7 MHz and third 455 kHz. Five IF filters are offered, from 16 kHz down to 300 Hz. The BFO will tune 8 kHz, so with 16 kHz bandwidth, can demodulate wide-band data transmissions. There is no internal speaker, so I have rigged up a pair of old computer powered speakers to the Line terminals on the back, cunningly wired so that in ISB mode the LSB signal comes out the left speaker, and the USB signal out the right! You can tune stations with stereo effect!


The Watkins-Johnson WJ-8718A/MFP receiver

24. Regco (RACAL) RG-5554A (1983)

This is a large rack-mount surveillance receiver, covering 20 - 1000 MHz AM/FM/CW/USB/LSB/ISB, and includes a panoramic adaptor. I doubt if there were ever many of them made, and even fewer in this country. It can be remote controlled via IEE-488, and has a channel stepping time of 5 ms. It has an oven-controlled frequency reference. There are two synthesisers, providing for double conversion. The first IF is tunable, and the second IF is 21.4 MHz. The receiver is largely controlled by keypad instructions, but includes a rotary encoder for tuning. It's heavy - 27 kg, and rack mounted.

Unfortunately my Regco has a power supply fault. I have the manual, so there's hope of getting it going again. It is also in need of restoration and a good clean! Other than the manual, I've seen no other information about this receiver anywhere.


The RACAL REGCO RG-5545A Surveillance Receiver

25. Icom IC-R71E (1984)

The IC-R71 is a very popular short-wave receiver, primarily because it is easy to operate. It also has plenty of useful features, and some models have a remote control, IF shift and an FM detector. There are optional filters and a range of other after-market goodies for this receiver. Primarily intended for a 50 Ohm antenna, there is however a random wire input for frequencies to 1.6 MHz.

Frequency coverage is 100 kHz to 30 MHz, although the LF end is marred by interference generated by the vacuum fluorescent display. Frequency readout is to 100 Hz, and there are 32 programmable memories (more with some options). My version has after-market filters, giving four bandwidth options (15, 6, 2.3 and 0.5 kHz). The first IF is 70.45 MHz, the second IF 9 MHz. The FM module includes a third conversion to 455 kHz.

The receiver will operate from the internal 110/230V AC supply or 12V DC. It has AM, FM, USB, LSB, RTTY modes, has AGC operated squelch and a notch filter. It has selectable AGC speed and a reasonable noise blanker. It also has a scan function, which I've never bothered with. The main advantage of the receiver is quick tuning - you can dial up any frequency directly from the keypad. Shortwave reception is excellent, with good audio quality provided you use an external speaker.

The receiver is nicely packaged and built, with a diecast front panel, weighs 7.5 kg, and dimensions are 111 x 286 x 276 mm.


The popular Icom IC-R71E

26. AOR AR-2002 Scanner (1985)

The AR-2002 had a long manufacturing career. Mine dates from 1985. By modern standards it's a bit slow, and it has a few problems, but it is still a useful scanner. It covers 25 - 550 MHz and 800 - 1300 MHz. It has AM, NBFM and WBFM modes and 20 memories, which are maintained (for a limited time) by a supercap. The display is LCD, but the viewing angle is limited and the backlighting not very helpful. The keypad is not lit. The signal strength meter is a row of coloured LEDs, and is really excellent.

The biggest problem is the keypad, which has become unreliable, but improves if you use it enough. The receiver is quite small (138 x 80 x 200 mm), and has a distinctive sloping front. The case is plastic. The unit operates from 12V DC (plug pack supplied), and includes a clock which is displayed when the receiver is turned off. The receiver has plenty of audio, with good response, making listening to FM broadcast a pleasure. Sensitivity is reasonably good provided you use an elevated antenna (to avoid receiver-generated noise). It comes with a short telescopic whip antenna.

Unusual for the time, the receiver includes a rotary dial, and has a choice of tuning speeds (step sizes).

There was an optional remote controller, for use with a computer. I have this unit, but it is of limited use - it generates considerable interference in the receiver, and the commands are very primitive. It does however let you tune to frequencies not available on the front panel - for example down to about 16 MHz.


The AR-2002 scanner

27. Plessey PRS 2282A (1985)

The 2282A is considered by many to be one of the best HF monitoring receivers ever made. Apparently only 400 were made, and I have one! The receiver is quite large, but has pleasing looks and is laid out well for easy use. Like the Watkins-Johnson further up this page, it's a premium monitoring receiver, not a ham receiver, so does do some things differently, such as locking the dial when you enter a frequency on the keypad, or selecting the bandwidth and AGC speed for you when you change modes.

The modes offered are CW/AM/USB/LSB/ISB/FM. The display uses large 7-segment red LED digits, and displays down to 1 Hz. There are smaller LED displays for other settings, and a linear LED display which indicates audio level, zero beat (like a phase meter), or RF level.

The receiver has six filters, from 8 kHz (AM) down to 300 Hz (CW) plus separate USB and LSB filters, since the receiver offers ISB operation. The receiver uses a 1 MHz precision OCXO frequency reference for all oscillators, with an external reference option, and offers 10 Hz tuning steps. The first IF is 65 MHz, and the second IF 1.4 MHz. The first mixer is a high level FET full bridge, and the second mixer a FET half bridge.

The receiver is rack mount, 177 mm high and 380 mm deep, and weighs 16 kg. There are no top or bottom covers provided, since the unit is generally mounted in a rack or an after-market cabinet.


The Plessey PRS 2282A Receiver

28. Transworld TW100 (1987)

I have included this HF transceiver in the collection because of the interesting technical developments it incorporates. This unit has no RF amplifier or preamp, and yet it uses a passive (diode bridge) mixer without any sensitivity disadvantage. The mixer incorporates a duplexer for image termination, and there is a high intercept IF amplifier before the 75 MHz roofing filter. Oscillator drive to the mixer is +10dBm! The first injection uses 10 kHz steps from the synthesizer, giving the transceiver a range of 1.6 to 30 MHz, and down to 0.5 MHz on receive. The second conversion oscillator operates in 100 Hz steps, and this is the minimum step size of the transceiver. The second IF is 1650 kHz. Both synthesizers operate from an OCXO reference, although oddly the BFO (which is acted on for RIT) is a simple VCXO, with less than perfect stability. The receiver is a bit tiring to listen to on noisy frequencies, as the filter is wider than normal (allows wide digital modes to be used), the AGC is always fast, and there is no RF gain control. The receiver has excellent voice-operated squelch.

The transceiver has no 'tuning knob', and very few controls. It has 100 pre-programmed channels, only one of which can normally be front-panel programmed by the user. Channels are selected and programmed via the keypad. There is a small LCD display which shows channel number (by default) or operating frequency to 100 Hz resolution. The transceiver can be programmed to operate split-frequency.

The transceiver is microprocessor controlled, and has an unusual feature to eliminate interference from this source: the micro is asleep while the transceiver is in use! It operates solely on interrupts, from the keypad, from the pressel switch and the few front panel buttons. Once the required action has been completed (say changing frequency, or going to transmit and updating the display) the micro goes to sleep again. In fact the microprocessor board is not in any way shielded, rather, the rest of the transceiver is!

Apart from the power amp and the microprocessor, most of the transceiver is built into a series of up to 12 diecast boxes, stacked in two layers behind the front panel. These are interconnected at the back by SMA connectors and copper hardline, and at the front with Molex connectors for low frequency signals and power. The case has a diecast rear, incorporating the PA heatsink, and a diecast front panel. The chassis and side rails are heavy Aluminium, and the covers are Aluminium sheet. The transceiver is quite large (107 x 350 x 450 mm) and quite heavy (13 kg), as it includes the AC power supply.

The transceiver operates 125W continuously, and will operate from 12V DC or the internal AC supply. The PEP power on SSB is about 150W, as the resting voltage on the PA from the unregulated supply is about 19V.

The TW-100 operates A3J (USB, LSB), A3H (compatible AM), CW and RTTY. It has numerous other features, such as voice squelch, channel scanning and selective calling. There are only two knobs, audio gain and clarifier (RIT), so no RF gain control, and there is no illumination on the front panel apart from the power LED. The keypad glows in the dark! This is a very simple transceiver from an operator point of view. It was designed for the diplomatic and NGO market. My unit's previous owner was reported to be the US Embassy in Wellington. I use this transceiver regularly for digital modes on the lower HF bands, and it has proved to be highly reliable and bullet-proof.


The Transworld TW100

29. Kenwood TKM-707 (1989)

Designed at a time when Amateur receivers and transceivers contained a mass of circuit boards with connectors and wires everywhere, the TKM-707, built to a completely different requirement, is deceptively simple inside. There are only two boards - the receiver and exciter, and the PA assembly. Unfortunately mine is missing the latter, so it is essentially a receiver with +10 dBm output capability. I have had to replicate some of the functions on the missing PA assembly, such as +10V regulated supply and antenna switching. But when you look inside the cover, the contrast of the simple design to the average complicated ham rig is startling! Yet the result is a high-performance, reliable transceiver with commercial use specifications. One of the secrets to the apparent simplicity is the use of thick-film hybrid devices.

The TKM-707 uses a 71.3 MHz first IF with a monolythic roofing filter, and a 10.695 MHz second IF with a single crystal filter. The synthesizer generates both injection oscillators via different loops. The transceiver does not operate LSB or CW: only A3J (USB) and A3H (compatible AM). There is no RF gain control, and the AGC is always fast. However the transceiver is ideal for digital mode operation, and it is in 24 hour service on 40 metres at present.

Nominally a marine transceiver, there are internal switches and links that will allow the user to set the operating frequency from the front panel, and/or program the memories. With these changes the transceiver will operate anywhere using the main tuning knob. The receiver incorporates excellent syllabic squelch. In the top right corner of the front panel is a small hinged cover which hides lesser used controls and a full numeric keypad. The transceiver is very stable, as it incorporates a simple OCXO reference for all oscillators. It operates from 1.6 to 23 MHz, and will receive from 500 kHz to 30 MHz. Power is external 13.8V, and the unit is quite light (especially without the PA!). The case is sheet Aluminium, with a robust plastic moulded front panel over a heavy Aluminium sub-panel. The dimensions are 270 x 96 x 270 mm.


The Kenwood TKM-707

30. Drake R8A (1995)

This is my currrent favourite receiver. It operates 100 kHz to 30 MHz, and like some of my other receivers, incorporates state-of-the-art design features (for the time), such as excellent band-pass filters, passive first and second mixers, and an image rejecting (I&Q) second mixer configuration which permits conversion directly from the 45 MHz first IF directly to 50 kHz. The second IF employs a series of LC filters to provide bandwidths of 6, 4, 2.3, 1.8 and 0.5 kHz. There is a conversion from 45 MHz to 455 kHz for FM reception. The three synthesizers and BFO are referenced to a single 35 MHz reference crystal. The passband tuning is achieved by interpolating two synthesizers in opposite directions.

The demodulators are double-balanced, and the AM demodulator allows for a Synchronous mode, which reduces distortion on short wave signals. The operating modes are AM, AM Sync, USB, LSB, CW, RTTY and FM. The receiver is microprocessor controlled, and the micro has a rear-panel RS232 connection, allowing the receiver to be remote controlled. I have written software to control the receiver and report its status in real time (see picture below).

I have had to restore the receiver, by reversing some unfortunate modifications and completely dismantling the front panel in order to clean the panel and switches. Before I did this work, the receiver could not be controlled at all. The switches are of the type with a rubber moulding containing a carbon rubber button, which presses on carbon ink contacts printed onto a circuit board. After cleaning and abrading the buttons, and cleaning the ink contacts, full operation was restored. The case responded well to a clean and polish and some paint touch-up. The covers and chassis are sheet Aluminium, and the front panel is extruded and machined Aluminium, backed by a sub-frame supporting the display/switch circuit board.

The large and pleasing display is a back-lit LCD type, with annunciators for modes and settings, and alphanumeric display for frequency and memory names. Frequency display resolution is 10 Hz, the same as the synthesizers, although you can choose to see fewer digits. You can also choose to display and control the receiver in kHz or MHz.

The only really annoying features of the receiver are the sluggish and non-weighted main tuning control and the soggy feel of the push-buttons. I have lubricated the rotary encoder and fitted a weighted tuning knob, which helped, but little can be done about the push-buttons, which tend to mis-operate unless carefully and accurately pushed. Rubber membranes may be robust, but they are a poor choice for a receiver where they are used all the time.

The receiver dimensions are 334 x 134 x 330 mm, and it weighs 5.9 kg. The R8 will operate from 12V DC at 2A, or from the internal 110/230V AC supply.


The Drake R8A receiver

ZL1BPU remote control software operating in Win7

31. Signal Hound USB-SA44 Spectrum Analyser (2010)

So why is a spectrum analyser part of my receiver collection? Well, because it also makes an excellent wideband receiver! With the software it came with, there is a receiver mode with limited capability, but the manufacturers recently released driver software to operate with HDSDR, a popular Software Defined Radio program.

It is an odd fact that this 'receiver' predates all my modern SDR receivers, yet wasn't considered a serious receiver until recently, with the release of the driver. The SA44 covers 1 Hz to 4.4 GHz, has a huge dynamic range, a 1ppm TCXO reference (or external 10 MHz reference), and resolution bandwidths from 0.1 Hz to 5 MHz. The amplitude range is up to +10 dBm and the sensitivity can be as high as -160 dBm with the preamp on.

Measurement accuracy is 1% and 0.25 dBc up to 1 GHz. Operated with HDSDR, it has all the features you'd expect of a modern SDR, such as adjustable passband, noise blanker, notch filters and all possible modes including wideband FM and DRM. With HDSDR it also has calibrated spectrum displays and a calibrated S Meter.

The unit is of course USB powered. It is contained in a small extruded Aluminium box, 170 x 80 x 27 mm. It has an SMA input connector and status LED on one end, and two BNC connectors, for 10 MHz external reference and Sync/test output or Trigger input at the other.

In receiver mode it has a maximum bandwidth of only 250 kHz, but it is much more robust than the usual SDR. I bought the SA44 new, and it makes a very useful portable spectrum analyser (and receiver!) when operated with a laptop computer.


The Signal Hound USB-SA44 spectrum analyser

32. Digitech AR-1733 FM/MW/SW/LW/AIR receiver (2012)

This small unit is a true short wave receiver, as it operates 2.3 to 26.1 MHz AM, as well as 153 - 279 and 522 - 1620 kHz AM, and 88 - 108 MHz FM. It also operates 118 to 137 MHz AM (the Air band). The receiver will operate off two AA cells or two AA NiCd cells, which it will charge from 5V using a built-in charging function. There is a built-in telescopic whip antenna, internal ferrite rod for LW and AM, but no external antenna socket. There is no BFO or SSB reception. Sensitivity is good, and the choices of bandwidth provided are ideal.

The receiver is touted as a DSP radio, and has some DSP-related functions. There are wide and narrow filters in AM modes, and squelch on the Air band. There is a stereo decoder in FM mode. It uses digital demodulators and filters and digitally controlled volume.

The synthesizer is very smart, and will step in 9 kHz or 10 kHz steps to suit the AM band in the user's country. The tuning control has two speeds. Slow step sizes are 1 kHz (AM) and 10 kHz (FM), while fast steps are 3 kHz (LW), 5 kHz (SW and Air), 9 kHz (AM) and 100 kHz (FM). There are 500 memories, arranged in 10 pages. The memories are a bit complicated to use, but in all other respects this is an impressive radio, and fun to use.

The receiver has up/down buttons in addition to the tuning knob, and will accept direct entry of frequency or memory number. Battery life is very good. The display is back-lit and easily read. The clock is displayed while the receiver is off. The dimensions are 125 x 75 x 50 mm, and it weighs 232g. It runs forever on a pair of AA cells.


The Digitech AR-1733 receiver

33. GMYLE (Fulljoin) PPM001 FM/DAB receiver (2013)

This little unit isn't a communications receiver as such, but it does represent a step into new technology. It receives VHF FM broadcasting and Digital Audio Broadcasts (DAB), so is my first digital receiver. The sensitivity in DAB mode isn't ideal, which is probably a reflection on the technology, the distance from and the low power of the local DAB stations, rather than any shortcoming of the receiver. It receives both DAB and DAB+. The former seems to have fewer dropouts, and the latter dropouts with annoying loud buzzing. The audio quality of the DAB mode is subjectively better, absolutely no discernable noise, amazing presence and clarity. Audio quality is nothing short of stunning.

I know almost nothing of the technical details of the receiver. It is ETSI 300 401 DAB compliant, and receives 175 to 240 MHz DAB. In FM mode it receives 88 - 108 MHz FM and has RDS functionality as well. It has a built in 700mAH LiPo battery which charges from 5V, with very good operating life (7 hours operating, and a very long shelf life). The unit has 30 station presets each for FM and DAB. There is no loudspeaker capability, just headphones, which double as the antenna. There is a socket at the bottom for a Micro SD card, and it will record to and play from the SD card.

The receiver is simple to use, and has a good 128 x 64 FSTN display with backlighting. The only annoying thing is that it is very easy to bump the controls, especially the on/off switch, while the receiver is in your pocket. The addition of an AM mode would have improved utility, and would serve to illustrate how much better DAB reception can be! The receiver is only 94 x 54 x 14 mm and weighs just 64g. It easily fits in your pocket. The battery is internal, LiPO technology, and is charged via USB.


The GMYLE PPM001 DAB receiver

34. RTL2832 R820T TV stick with direct sampling (2013)

These little devices were designed to provide low cost (US$12) DVB-T (Digital Terrestrial TV reception), DAB and FM reception, but smart guys have reverse-engineered the devices to provide reception of other modes as well - NBFM, AM, SSB and CW to name just a few of the possible modes. These units are powered by USB, and transfer their data to a computer at high speed for further processing. They are of similar size to the usual memory stick.

There are two main chips within the device, a wideband tuner and a baseband chip (high speed 8-bit digitizer). The device used here has an R820T tuner chip and an RTL2832 baseband chip. It is compatible with both SDR# and HDSDR software, plus many more packages for Windows, Linux or OSX.


The R820T TV stick

I have modified this device to provide direct sampling for MF and HF reception, by fitting a tiny toroidal transformer inside the stick. This trick bypasses the R820T tuner and applies the antenna directly to the baseband chip via the unused Q+ and Q- inputs. (The R820T chip is connected only to the I+ and I- inputs). So by selecting the baseband chip mode in the software, I can use the stick and HDSDR for 100 kHz to 30 MHz, and with SDR# for 24 to 1766 MHz.

While quite different to a conventional receiver, performance is remarkable. On MF and HF (where the tuner's low-noise preamp is not available) sensitivity is modest, but quite adequate with an active antenna or on naturally noisy HF bands. The receiver would benefit from a preselector, which would lower the noise floor on this simple 8-bit direct digitizer. A bandwidth of 1 MHz or more can be seen on the receiver panoramic display. In this mode (first picture), the stick with HDSDR operates AM, AM Sync, FM, SSB, CW and receives wideband modes such as DRM. Using external software, the unit can also be used for SSTV, DRM and other digital mode reception. Filters can be set to any required bandwidth. Stability and frequency accuracy are impressive, giving much better results than using an up-converter.

In VHF mode (second picture), using the SDR# software, NBFM, wideband FM and AM operation are possible. Software includes squelch, memories and scanning features. Here the tuner chip is used, and sensitivity is impressive. I've used this receiver for weather satellite reception. Stability and frequency accuracy are quite adequate.

   
The R820T TV dongle (direct sampling mode) receiving on 13.7 kHz with HDSDR (left), and the R820T TV dongle (in tuner mode) receiving a weather satellite on 137.9 MHz with SDR# (right).

35. Afedri SDR-Net (2013)

This unit is a purpose-built 12-bit Software Defined Radio. It operates from 100 kHz to 30 MHz using 80M samples/sec direct sampling with digital down conversion. It can process a bandwidth of up to 1.85 MHz when communicating via a network, although I've had no success operating it in this mode. Output in USB mode has a bandwidth of up to 230 kHz. It can be powered via USB, although is best with a separate supply, as the current is rather high for the usual USB port (7.5V at 400mA). The unit is small - 120 x 78 x 27 mm. It is housed in an extruded Aluminium box with Aluminium end plates.

The Afedri SDR-Net can be used with standard SDR software such as HDSDR, and comes with a cross-platform control program which acts as the driver DLL. Using HDSDR, performance is quite good, but after using the cheap ($12) RTLSDR dongle with more than 1 MHz bandwidth, it is hard to justify the small benefits of this unit against the higher cost (more than 10 times). The unit has much improved noise floor if an external preselector is used.


The Afedri SDR-Net unit

36. RTL2832 R820T TV stick V3 (2016)

Functionally similar to the TV stick receiver previously described (item 28), the so-called 'V3' TV stick has quite a few advantages. Although it uses the same chips and provides 8-bit reception, the 'V3' has been purpose-designed to provide the direct sampling option. It also has a robust metal case, improved heat management, and a TCXO frequency reference for much improved frequency stability. The V3 performance is better at low frequencies than my home-adapted version - it performs well down to 300 kHz and adequately down to 10 kHz. It will hear the Russian 'Alpha' station at 11 kHz.


The V3 TV stick

As you see, the the V3 has an SMA antenna connector, which is used in both the normal VHF/UHF mode and in LF/MF/HF direct sampling mode. In the example below, the V3 is operating on a Linux Mint platform, using Gqrx software. Note that is is receiving on the AM broadcast band in direct sampling mode. Switching between modes with this software is cumbersome, but not difficult.


The V3 operating with Gqrx on 702 kHz

37. SDRPlay RSP1 (2016) and RSP2 (2017)

These two receivers are purpose built high performance 12-bit SDR devices. The RSP1 has a single antenna port, and a plastic box, while the RSP2 (pictures below) has three antenna ports, which are software selectable, and a choice of metal or screened plastic box. The RSP2 also has an 0.5ppm TCXO reference. I have the metal box version (the 'Pro' option), which also has connectors for reference clock input and output (this allows multiple receivers to operate synchronously).

       
The RSP1 (left), RSP2 (centre), and RSP2 Pro receivers

The RSP1 operates from 10 kHz to 2 GHz in one range, while the RSP2 has continuous coverage from 1 kHz to 2 GHz. The RSP2 balanced LF input is high impedance and operates from 1 kHz to 30 MHz, while the A and B (SMA coaxial) 50 Ohm inputs operate from 1.5 MHz to 2 GHz. Both receivers have up to 10 MHz IF bandwidth, assuming the USB link and computer are fast enough, and with appropriate software can be used to receive multiple stations (even in different modes) within a 10 MHz range at the same time.

The RSP2 has improved RF band-pass filters, improved RF gain management, and AM and FM band notch filters, which reduce intermodulation from very strong broadcast stations. The ability to switch antennae is extremely useful. The RSP2 is a better receiver than any of the conventional receivers I have, is more convenient and flexible to use, and of course was a lot cheaper than any conventional alternative.

My preferred software for these receivers is SDR Console, which currently supports the RSP2 in a beta version. SDRUno fully supports both devices. Both programs are free. The RSP1 also works with SDR# and HDSDR, and on an Android platform, with SDRTouch.


The RSP2 operating with SDR Console V3 beta, operating on 14.2 kHz,
and receiving a Russian 'Alpha' station during the day using the High Impedance antenna input


The RSP1 operating dual receive (NBFM) with SDR Console V3 beta,
on 76.2 MHz and 76.1125 MHz at the same time


The RSP2 operating on 92.6 MHz (FM broadcast, WBFM) with SDRUno software.


The RSP2 operating on 253.72 kHz in USB mode, (receiving an NDB)
on a Samsung Tab A (Android device) with SDRTouch.

SDR Console has superb graphics and is very versatile. While SDRUno looks simpler, and more like a conventional receiver, it does include separate windows for waterfall and spectrum displays.

38. August MB400 DAB Receiver (2016)

This smart looking radio is not your average old-style mantel radio. It supports Bluetooth reception (including NFC connection), will play from a USB stick or MicroSD card MP3 and WAV files, and shows track information on the display. Unusually for a portable radio, there's no handle, and it is not small nor light, but it has decent-sized stereo speakers, plenty of audio, and really good sound.

The MB400 is very well engineered, and quite robust. It operates from four C-sized dry cells or an AC adaptor, not supplied. Oh yes, and it's also a radio receiver, operating from 87.5 to 108 MHz FM stereo, as well as 174 to 240 MHz DAB and DAB+ (Digital Audio Broadcast). There is no AM mode. The receiver includes RDS station information in FM and DAB, and uses a back-lit LCD display.

         
The August MB400 mantel radio front (left)       and rear (right)

The receiver performs superbly, with good clarity, good bass, and pleasantly low noise (given enough signal). In DAB mode there is simply no noise, and excellent dynamic range. The DAB fuction is able to set the clock, and it can be set manually if DAB isn't available. The controls are fairly easy to understand and use.

One unusual aspect of the MB400 is that the only antenna provided is a random wire, which is wound up in a recess at the back (see rear view). I guess it is intended as a mantel radio, but in this day and age a telecopic whip or an antenna connector would be preferable. Unless signals are very strong, it does not receive anything with the antenna wound up, so it's not that practical as a portable receiver, but still great as an MP3 or Bluetooth player. When I've summoned up enough courage, I think I'll add an antenna connector on the back.

39. Rolton T50 FM/MW/SW Receiver (2017)

Manufactured by ShenZen Mando Technology Co. Ltd, this cool little radio is a pocket-sized powerhouse. I use that term intentionally, as it runs from a huge 1500 mAH Li Ion cell, which seems to last forever! It is charged using a USB cable.

The radio covers FM 64 to 108 MHz in two bands (mono only), MF 520 to 1710 kHz (both 9 kHz and 10 kHz spacing offered), and eight short wave bands from 5.6 MHz to 22 MHz. It also features a decent LED torch and a uSD card slot. Even better, you can transfer music to and from the uSD card via the USB connection!

There is a ferrite rod antenna for MF and a fairly small telescopic whip for HF and VHF. Despite the small antenna, performance is adequate. The case is ABS, but is lacquered to give a bright and shiny appearance. There's 1W of audio available, and there's a passive radiator which helps improve bass response from such a little box (132 x 30 x 66 mm). Audio clarity is excellent.

In recent years just about every radio has used an LCD display to extend battery life, but this little guy has power to burn, and features a bright red LED display, easy to see except in direct sunlight, and really useful at night.

The radio has direct frequency entry on all bands, plus up/down buttons. Frequency entry within band is easy enough, but the radio is split into 12 bands, which makes life complicated, as you have to check the band range in the manual in order to get to where you want to go, as if the frequency is not in the current band, the command will be ignored. Fortunately the manual is in reasonable English, and the same size as the radio, so not difficult to carry around.

The radio plays MP3 and WAV files really well. However, there is no track display other than a number, so finding a particular track is something of a trial. There are basic search, scan and pause functions, but no random play. Audio quality from file is very good.

There is a clock function, and the radio features auto-scan, although with no information displayed about the stored memories, finding a particular radio station from memory is again pot luck. On all bands, reception is reasonable if the signal is strong, but weaker stations are masked by buzz noises and whistles generated within the radio.

In terms of value for money, compare this radio (it cost me US$17) with the Sony ICF-2001, which in 1980 cost about US$350, or about six weeks' wages.


The Rolton T50 pocket rocket

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