UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - GEC-Marconi single-frequency HF Rx

Julesomega · 7th Apr 2020, 9:49 am

Thanks David, I hadn't thought through the frequency relations to include the 1st filter. At first I wondered if it was low VHF despite the "HF Module" name.

The stages sequence seems to be bandpass tuned RF amp with capacitor top-coupling, followed by a Minicircuits mixer, VHF crystal filter, mixing back down to 10.7. The front end is designed for a high TOI level, maybe intended for use on a survey vessel. Looks to be a single device mixer after the 1st filter. We won't have much more to go on until I unsolder the 1st filter unit for a look. I'll see if I can work out the supply lines.

You are right that the demodulator output would be low with NBFM, maybe that's why there is an OP82 nearby.

7th Apr 2020, 9:49 am	#3
Julesomega Nonode Join Date: Dec 2012 Location: Stockport, Greater Manchester, UK. Posts: 2,113	Re: GEC-Marconi single-frequency HF Rx Thanks David, I hadn't thought through the frequency relations to include the 1st filter. At first I wondered if it was low VHF despite the "HF Module" name. The stages sequence seems to be bandpass tuned RF amp with capacitor top-coupling, followed by a Minicircuits mixer, VHF crystal filter, mixing back down to 10.7. The front end is designed for a high TOI level, maybe intended for use on a survey vessel. Looks to be a single device mixer after the 1st filter. We won't have much more to go on until I unsolder the 1st filter unit for a look. I'll see if I can work out the supply lines. You are right that the demodulator output would be low with NBFM, maybe that's why there is an OP82 nearby. __________________ - Julian It's good here