Andy Howlett from Dukinfield near Manchester UK, describes his simple but highly effective SSB/AM Transceiver designs which employs a Minicounter for its frequency display.

"Here's a photo of my homebrew Topband SSB/AM rig which uses the Cumbria Designs Minicounter for the frequency and mode display. The design is absolutely 'bog-standard' and makes much use of the NE602 balanced mixer chip". 

Transmitter

"On SSB the Transmitter uses one NE602 for the balanced modulator operating at 453.2kHz (followed by a 2.7kHz ceramic filter) and a second, slightly unbalanced NE602 at 455kHz to generate AM. The AM modulator is followed by an 8kHz ceramic filter. The 455kHz IF is mixed with the VFO (~ 2.5MHz) to the transmit frequency by another NE602. Careful LC filtering takes care of the image around 2.8 MHz. Output power is up to 20 Watts PEP from a pair of IRF740 FETs working from a 40-volt supply. I've attached a photo of the Topband PA undergoing tests (spot the solder blobs). Those little IRF fets are almost unburstable, aren't they? I found I could thrash about 40 watts out of them! " 

Receiver

"On receive, a double tuned bandpass filter is used as the preselector. This is followed by a dual-gate mosfet RF stage and a NE602 receive mixer to convert the signal frequency down to 455KHz. IF filtering is identical to that of the transmitter with a 2.7kHz ceramic filter for SSB and an 8kHz filter fofr AM. Thereafter it's a fairly standard IF amplifier/product det (not a 602!) and audio amplifier line up. The Minicounter measures the VFO frequency and subtracts 455KHz for a direct frequency readout, and it does this without fuss or hiccups. Without this little module, tuning the rig would be largely guesswork!"

On the Air

"The rig works very well - I get excellent audio reports on both SSB and AM. The microphone signal path includes a compressor, and on AM the 8KHz wide IF filter ensures that both sidebands are transmitted. Living in a small terraced house brings problems for topband fans. Limited space precludes vast dipoles or even inverted L's and so the only way was upwards. I use  a homebrew 30ft vertical based on a fibreglass roach-pole. It's loaded just over half way up and works against a tiny (approx 10 x 10 ft) earth mat buried underneath the garden. The vertical antenna is used for TX only, as the noise on receive is something to behold! On receive I use a Wellbrook loop antenna, which almost completely ignores local noise. I'm not really a DXer - I have a background in broadcast AM radio and still fascinated by ground- wave coverage, so I'm quite content just passing the time in the local and semi-local nets".

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Images

(Click to expand)

Fig.1 Transceiver

Fig.2 PA under test