70MHz Receive Converter GW4RWR
Introduction
Originally I placed the first MOSFET in a separate enclosure that could be tower mounted, to minimise feeder loss. In practice I've avoided this option, the antenna is connected to 'shack' by 30m of LDF4-50A; I don't feel that loss is excessive on receive.
Results?
The diecast enclosure contains BF-981, then two band pass filters and resitive pad before the SBL-1 double balanced mixer. The 10.7 output passes to a BF961 (with AGC applied) and then through a 15kHz filter which limits the spectrum reaching the final BF-961. There has been no attempt at a noise blanker, although I did consider a parallel 10.7 output, perhaps unfiltered, to feed an external, digital receiver. A bit short of space for that, though.
The schematic doesn't show damping resistors (1k-3k9) that were necessary across all the 70MHz inductors. It depicts the masthead rx amp version, whilst the 'all in one' version has the 470R from drain connected to the hot end of the first BPF, with DC fed from the cold end, under the board.
A final addition was buffered rx out to an external rx (my FT-707 with its CW filter)
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It's perhaps a touch more sensistive than my transverter/HF TRX combination.
I can copy GB3ANG without the BF-981 front end.
