Someone was asking me about PMR conversions the other day, which set me reflecting on all the sets I've worked on over the years. I started off in 1982 with a pair of the (then) ubiquitous PF1s, and have since worked on more than 50 sets, learning a lot about radio design in the process!
In many cases, I had the circuit diagrams of the sets to help me, but in some cases I had the challenge of a "reverse-engineering" puzzle to figure out how they worked.
Here are a few details of my experiences:
An amazing example of 1960s miniaturisation - all discrete circuitry. They were single-channel crystal-controlled sets which introduced me to ordering crystals from the Quartslab company. The transmitters ran off an 18V battery (which was half the size of the set) and gave out around 100mW, and featured a spring-loaded steel rod aerial which could easily have your eye out. The repeater could only be accessed via a manual whistle: I remember struggling once when I'd had a tooth filled and couldn't access GB3MA until the anaesthetic had worn off!
The receiver was a separate unit, which meant that I could listen on the repeater output whilst working through it. It ran off 9V, and had a battery-economiser which gave out a comforting ticking noise. I had four pairs of these, each crystalled for a different channel.
These were ex-Met Police handies which were solid enough to serve as truncheons too! I converted and crystalled three of these for a 2m local net.
An unusual AM/FM set with an early PLL synthesizer. The conversion involved changing the IF from 21.4 to 10.7MHz, as the VCO wouldn't pull far enough for simplex operation with the high IF. I achieved 25W output, and full coverage of the band in 12.5kHz steps. I still have this set.
Another AM/FM set, but with provision for 10 pairs of crystals. I converted three of these, with 3 channels and 25W output. A couple of the TO5-can transistors do get very hot on transmit, so short overs are the order of the day.
I used one of these in the car in the 1990s, when some parts of the country used AM rather than FM, so I could use either mode at the flick of a switch.
Starting with the same low-band sets, I modified all the tuned circuits to bring them down to 51MHz, fitted 2 crystal channels, and set the output around 15W. I did two of these, one of which I still use.
These were compact units with the familar Pye miniature discrete circuitry. I added a little audio amplifier, and converted them into little monitor receivers. I even did a couple for the AM airband, which entailed adding a primitive AGC loop before the detector.
A synthesized FM set with around 10W output. I converted four of these, programming 100 12.5kHz channels and adding a 1750Hz access tone.
I used one of these mobile and home-base for many years.
A meaty mobile set capable of over 30W output. Programmed by a diode matrix, it originally had six channels, but by re-designating one of the front panel switches, I gave them another six. I did two of these sets, one of which I used mobile for a while.
Single-channel crystal-controlled mobiles. I did two of these for the local repeater. I recall that I forgot to disable the tx mute on the one I did for a friend, so he found that he couldn't transmit while his squelch was open. No big deal you may think, but as he had to whistle up the repeater access tone, he couldn't then check the output to see if he'd hit the right note, or he'd have to wait for the time-out and try again!
These were very nice 10W synthesized sets. I couldn't get the PROM devices for them, so I designed a little PCB to carry an EPROM instead, and included a toneburst unit too. I did seven of these, and still have one, with 80 channels.
These don't count as ex-PMR sets, but I did convert a couple of them for the 10m band. The modification used a BCD adder to translate the channel numbers into the 29MHz band. I even managed to add a -100kHz repeater shift too. I still have one of these.
A lovely "talking brick" handie with about 5W output, and 16 channels. I did two of these, and still use one of them. I managed to find a PROM to program it for the amateur band ok, but struggled to find an aerial to fit in the 1/4" UNEF thread on the top. In the end, I used the socket to cut its own thread in the soft brass on the bottom of a telescopic rod aerial.
I've used this set many times portable on 4m, and even worked into Denmark with it a couple of times. I've now found one of the very rare mic/accessory connectors for it, so that I can connect up an external aerial via co-ax too.
I cut open the battery case, and installed 1800mAhr metal hydride cells, which give lots of talk-time, even with 5W output.
Similar to the Lancer, but much better known. I built a programming interface, and set them up for eight channels on 70cm. They had a speaker-mic and charger too, and even CTCSS for repeater access.
I had two of these, but the second had a fault in the CPU section which I could never resolve: this is the only set to date which has defeated me.
I got this from the Plymouth Rally: it was a low-band set with four crystal channels, and looked just like the Yaesu FT202R: it even used the Yaesu 10.8V nicad pack for the FT207/208 series. The BNC antenna socket made it easy to connect external aerials, or a home-made helical I made, wound around a piece of wooden dowel.
A young Novice friend of mine got this from the Longleat Rally, and I helped him get some crystals, and tune it up.
I had a number of these very compact high-band handies, which I converted for 2m. They had four channels, but the miniature HC45 crystals were a bit pricey, so most of them only had one or two fitted.
A most unusual set, with joke-sized giant buttons on the front (may have been designed for users with gloves?). I programmed it with ten channels, mainly local repeaters, but you needed a good 1750Hz whistle to open them up..
I was given a few of these rather battered ex-Forestry Commission units by friends at the Cheltenham club. They have provison for six crystalled channels, and give a comfortable 25W output.
One of these has been my main 4m home-base set - it has all six channels fitted, and I added a 5W low-power switch and a squelch control. I must have made over 2000 QSOs on it over the last three years, and it cost me nothing!
A 40-channel synthesized handie. The PROM devices are now very expensive, but as I got the set for free, it was worth investing in.
It will give out 3W, but gets very hot on the side of the case, which helps to curtail long overs! Again, new metal hydride batteries give a good duration.
I've recently acquired a speaker-mic, on which I've fitted a BNC antenna socket for external aerial connection.
The ubiquitous 4m set of the last few years. I got mine ready-converted, but have since helped a few friends to upgrade theirs to the latest PA4DEN software (the VCO needs re-aligning after the new EPROM is fitted).
These sets do run hot, but I know one local GB2RS newsreader who manages 30-minute transmissions on his, with a fan blowing across the heatsink.
A friend gave me a pair of these, to see if I could do anything with them. They were the high-band TR models, complete with digital signalling board, for use in trunked radio systems.
The simplest way to get them onto 2m was to cut out the trunking board, and go back to diode-matrix programming of the synthesizer. For single or dual-channel operation, it was possible to build a simplified diode matrix (<20 diodes, rather than the full 64!) on Veroboard. Email me if you'd like a copy of the conversion details.
I now use one of these in my car: it's on 144.8MHz, to transmit my APRS beacon as I drive around.
I was given one of these single-channel crystal-controlled sets to have a look at. Unfortunately, most of the ferrite inductor cores were fractured, so it wasn't possible to re-align it into the amateur band. Also, it would have cost around £15 in crystals, just for the one channel. It's been kept for spares.
A friend asked me to see if I could convert one of these 16-channel synthesized sets for him. The synth was programmed with a (now very rare) PROM device, so I followed the suggestion in Chris Lorek's book and wired up an EPROM socket in its place.
I managed to get the EPROM right at the second attempt (the first time around I'd carefully arranged all the data in an 8-bit table, before realising that just the four LSBs are used - doh!)
I paid a tenner for a pair of these two-channel diode-programmed sets from the Lowton Rally 2006, and they even came along with a small box of spare diode matrix boards: if only I'd got these a few months ago, it would have saved my stock of Veroboard and 1N4148s!