How to reuse these excellent units on the Amateur bands
Add an S Meter Add a DDS VFO Recycled Crystals Making a Linear A Band Plan
Over the last 15 years or so, the commercial use of mobile HF radio has dwindled considerably. The same is true of marine MF/HF radio. As a result the older HF radios become redundant. VHF radio and cellular phone are now more popular - both becoming more viable with the maturity of the infrastructure involved.
Where do I find an HF SSB Radio?
Many end up in a junk heap at commercial radio repairers or marine agencies, and some can be found at Amateur Radio rallies, junk sales, or squirreled away in a friend's shack. Ask around! The type described here are the crystal-controlled 10-channel single conversion SSB type built in the 1970s and 1980s, which were widely used in Australia and New Zealand, and which represents the bulk of those available at sensible prices. You should be able to acquire one of these sets in good order for $40 or less. More recent synthesized commercial radios still command very high prices.
What can we do with these radios?
They make excellent spare HF radios, they are good for fixed links, great for setting up in the bach, boat or off-roader. Some of the smaller units make great portable sets. The larger units are easier to find, and have higher power - 100W - and additional features such as AM operation, a good noise blanker and excellent voice actuated squelch. Don't be put off because they are crystal controlled - this is why they are cheap to acquire, and there are several simple strategies for putting them on useful frequencies. Most of these radios will operate on 160m, 80m, 40m and 30m, and some will stretch as far as 20m. Even with just one working frequency, they can be very useful.Note - These conversions are for Radio Amateurs only - most of these sets do not now meet land mobile or marine type approval, and once you've made the suggested changes, they definitely will be for Amateurs Only! No warranty of performance or suitability of these mods for Amateur or any other purpose is intended or provided.
About Type Approval
Commercial Radio and Marine Radio installations must use type approved and professionally installed equipment. Type approved sets should ONLY be set up, installed and adjusted by licenced technicians using factory approved parts. Once a radio falls outside the approvals, for whatever reason, it's value is reduced. That makes it attractive for use on ham bands.
The CODAN models considered here are the most common types. All are rell built and reliable, and share a common 1650kHz IF single conversion arrangement. Most have the renowned voice operated mute option. Since these radios have all been discontinued, parts are hard to find (especially channel selection coils), so you may need to use parts from a spare unit.
Service information and parts are no longer available from the manufacturer. No service manual or schematic information is available from the author either, but can frequently be found on the web or various mobile radio forums. Some links to photos, manuals and other information are provided. No guarantee is given of the accuracy of the information given here or at any of the links.
Frequency Range 2 - 16MHz, 14 crystals 10 channel, single or two frequency simplex Modes SSB (A3J), USB with LSB option (extra filter) AM (A3H), automatic AM on 2182kHz Stability ±50Hz, -10°C to 50°C and ±10% supply variation Power Supply 12V, 10 - 15V (6801 Mk 2), 24V, 20 - 30V (6801-S Mk 2) Receive, 250mA A3J average voice transmit 6A (4A 24V) A3H, A3J two tone transmit 13A (7A 24V) Transmitter Output Power 100W PEP (120W 24V) IF and Selectivity Crystal Filter 1650kHz (SSB 300 - 2800Hz, 6dB; AM ±3kHz 6dB) SSB 70dB down at -1 and +4.2kHz AM 60dB down at ±14kHz Dimensions 340 x 360 x 112mm, 5.6kg Service Manual Download Manual
The 6801 is a large but very flexible unit, easy to work on. It has noise blanker, voice activated mute, and a very conservatively rated power amplifier. It comes in a green and cream colour scheme or nautical blue and grey. There is space on the RF/IF board for THREE crystal filters! The 24V marine version is usually cheaper, and gives a bit more output power. Apparently they can be 12V converted by simply rewinding PA transformers.
6924 Mk 2
Frequency Range 2 - 13MHz, 10 crystals 10 channel, single or two frequency simplex Modes SSB (A3J), USB with LSB option AM (A3H), automatic AM on 2182kHz with option Any two of USB, LSB, AM modes possible Stability ±50Hz, -10°C to 50°C and ±10% supply variation Power Supply 12V, 10.5 - 15V (case isolated) Receive, 100mA A3J average voice transmit 2A A3H, A3J two tone transmit 3.5A Transmitter Output Power 30W PEP (6924-S 35W) 8W AM (6924-S 9W) Antenna Whip or long-wire from 2.4m to 25m at any frequency within operating range IF and Selectivity Crystal Filter 1650kHz SSB 300 - 2800Hz, 6dB SSB 70dB down at -1 and +4.2kHz AM ±3kHz, 6dB AM 60dB down at ±12.5kHz Image rejection >65dB Dimensions 313 x 193 x 125mm, 4.7kg More Pictures Larger general view7727 Closer general view Front panel Inside view Internal view with hinge-out section open The 6924 Mk 1
The 6924 Mk 2 is a small portable unit in a rainproof "lunch box" with clip-on lid and built-in antenna tuner. A small compartment on the left side gives storage space for the microphone. The antenna and ground push-terminal connections are on the front panel. Colours are green and cream (6924 Mk 2) or blue and grey (6924-S Mk 2). The units are engineering masterpieces and easy to work on. An ideal radio for solar power supply (note receiver current).
The 6924 Mk 2 has been used in many out of the way places - off-shore islands, Antarctica, and throughout the Pacific. The author's unit spent most of its life on Little Barrier Island, callsign ZKMP7, in a Department of Conservation hut, powered by solar energy.
The older 6924 Mk 1 has a different arrangement both inside and out, and uses an inverter to power the transmitter. It is difficult to work on and not reconmmended.
Frequency Range 2 - 16MHz, 10 crystals 10 channel, single or two frequency simplex Modes SSB (A3J), USB with LSB option AM (A3H), automatic AM on 2182kHz Stability ±50Hz, -10°C to 50°C and ±10% supply variation Power Supply 12V: 10 - 15V, 24V: 20 - 30V Receive, 250mA A3J average voice transmit 5A (3A 24V) A3H, A3J two tone transmit 11A (6A 24V) Transmitter Output Power 100W PEP IF and Selectivity Crystal Filter 1650kHz SSB 300 - 2800Hz, 6dB SSB 70dB down at -1 and +4.2kHz AM ±3kHz, 6dB AM 60dB down at ±14kHz Dimensions 325 x 270 x 95mm, 4.5kg Service Manual Download Manual More Pictures Remote Control Version 7727TB8121 Marine Version
The 7727 comes in many versions, 12V/24V, marine and land mobile, local control and remote control. It comes in a green and cream colour scheme, black and grey, or nautical blue and grey. Above you see the land mobile version. The 7727TB (remote control version) is especially attractive as it has relay-operated channel change and so can be arranged for automatic band-change when using a local or remote micro controller and digital VFO.
Frequency Range 2 - 13.2MHz, 10 crystals 10 channel, single or two frequency simplex Modes SSB (A3J), USB AM (A3H), automatic AM on 2182kHz with option Stability ±50Hz, -10°C to 50°C amd ±10% supply variation Power Supply 12V, 10 - 15V Receive, 100mA A3J average voice transmit 2.5A A3H, A3J two tone transmit 6A Transmitter Output Power 60W PEP (15W AM) 2 - 9MHz 45W PEP (15W AM) 9 - 13.2MHz Antenna Whip or long-wire from 2.4m to 25m at any frequency within operating range (approx 1/16 to 1/4 wavelength) IF and Selectivity Crystal Filter 1650kHz (SSB 300 - 2800Hz, 6dB; AM ±3kHz 6dB) SSB 70dB down at -1 and +4.2kHz AM 60dB down at ±12.5kHz Dimensions 280 x 212 x 140mm, 3.6kg More Pictures Larger general view Front panel Rear view
The 8121 is a small marine radio, with internal tuner and permanently connected microphone. The antenna connector stud and ground stud are on the back panel. It is intended for use with a random wire, untuned whip or backstay antenna. It comes in boatie black with white decals. The case is splash-proof and there is no external heatsink. Although a higher-powered amplifier is used, internally it is very similar to the 6924 Mk 2, and easy to work on. The standard 8121 lacks the Mute circuit, but it is easily added.
This model illustrates the remarkable longevity of the core design - 1969 to the mid-80's, and many of these radios are still in use today.