70MHz SSB Transceiver GW4RWR
Summary
My original intention was to make separate front-end, local oscillator, pre-mix and transmit boards to equip the FT-225RD for 70MHz, but it would have been a headache to change bands, and in any case I'd need an outboard PA, so I decided on a dedicated homebrew 4m radio. USB/CW modes were required, and the radio's performance should be at least as good as my modified FT-225. Being band-dedicated, it should always be on 70.2 when I’m in the shack, and would avoid messing around with an HF radio and transverter with all the cable and switching hassle entailed.
Single conversion to 10.7MHz means that the receive path can be filtered immediately after the first mixer, and subsequent transistors aren't subjected to a whole band full of signals, as they would if a transverter is used in front of an HF radio.
The modules
I learned the hard way that it's far easier to modify a project if it's split into discreet boards, and the easier each one is to remove, the better. Single boards save space, but I leave them to the experts
Receiving GB3ANG (Youtube link)
Conclusion
From left to right, the front panel controls are RIT/OFF/XIT, PA off, External LO in, AGC slow/fast, MOx; knobs for Band, LSB/USB/CW/AM, and the big one for the VXO. At the right side, clockwise from top left is Clarifier, IF gain, TX Power, (mic socket), MIC gain, AF gain. I shall try to standardise on this layout on the next radio that I build.
The cheap CB meter was chosen since its translucent perspex scale could be backlit; its recessed edges allow it to be pressed against the front panel, without falling through it. The narrow slit to the right of the meter contains LEDs for relative power indication. Right side panel contains LEDs for RIT, Sequenced PTT out to Amplifier, TX and External LO.
The rear panel has separate Tx/Rx sockets, spaced to mount a CX-520 relay if the radio is operated stand-alone. Alternatively it can be cabled directly to an amplifier with separate tx/rx paths. 'RCA' sockets for AF line-out, ALC i/p, PTT out to amplifier and +13 out to operate the CX-520. 3.5mm socket for external loudspeaker, large socket for the CW keying line. BNC sockets for external LO i/p and Rx IF o/p.
I have a few of these 2U cabinets, so a sister radio for 144MHz is planned. I have a further two spare SSB filters, and was planning a single conversion 7Mhz & 14MHz radio until I realised what a disaster this IF would be. Unfortunately 21MHz doesn't work either. Perhaps 14, 18 or 28MHz should be the target. Suggestions, anyone?
