- Recycled Radios -

INTRODUCTION

Over the last 10 years or so, the commercial use of mobile HF radio has dwindled considerably. The same is true of marine MF/HF radio. That's not to say that HF usage has decreased, as the mobile networks are being replaced by fixed service data networks instead, and one way or another the older radios become redundant. VHF radio and cellular phone are now more popular - both becoming more viable with the maturity of the infrastructure involved.

So where do all these old HF radios go, and what can we do with them? Well, many end up in a junk heap at commercial radio repairers, 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 here 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.

So 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 - they will in all probability negate type approval, and should not be used on any unit destined for commercial land mobile or marine service. Type approved sets should ONLY be set up, installed and adjusted by licenced technicians using factory approved parts. No warranty of performance or suitability of these mods for Amateur or any other purpose is intended or provided. You're on your own, mate!

MODELS FOR CONVERSION

The models considered here are the most common types. If you have information on other models, or Service Manual and conversion information for any of these radios, let the author know. These radios have all been discontinued and parts and information are not available from Codan. The information here is not supplied by Codan (except indirectly via available manuals), and all errors are those of the author.

6801

Frequency Range

2 - 16MHz, 14 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 amd ±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

Off-site link - select "Save Link Target As..."

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!

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 amd ±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 view

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 waterproof "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 6924 has been used in many out of the way places - 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.

7727

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 amd ±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

Off-site link - select "Save Link Target As..."

   

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 (top right) the land mobile version, below left the remote control 7727-TB, with its control head, and on the right the marine version.

8121

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. The antenna connector stud and ground stud are on the back panel. It comes in boatie black with white decals. Internally it is very similar to the 6924 Mk 2. This illustrates the remarkable longevity of the core design - 1969 to the mid-80's, and many of these radios are still in use today.

Copyright © M. Greenman 1997-2005. All rights reserved. Contact the author before using any of this material.  HOME