The bypassing is now in place. A 100nF cap from pin 1 to pin 11 of the mixer ICs pads (remember that the IC isnt there!), this effectively connects the secondary of L3 to the supply rail. Since this system uses a combined power/signal line, that should now be feeding the receiver. A temporary link takes the other side of the secondary to ground. One leg of a 680 ohm resistor has been lifted to isolate the DC from the secondary, and a final temporary link jumps the missing L4 secondary to re-establish the DC supply to the front end transistors.
With the NAVTEX receiver in spectrum test mode, I can now see 'noise' where-as before this was totally blank, unless I put a finger on the supply wire. I can get a peak to appear on the display if I crank up a 518kHz signal from the Marconi 2955 test set. This is air coupled from a whip antenna, and had to be cranked up to about -20dBm output, but moving the antenna and its feeder around near the whip does suggest that the pick-up is by the antenna and not via the feeder or any other means. So far so good, but the proof of course will be whether it actually receives a NAVTEX transmission!
I have the station reserve receiver tuned to 518kHz as well to compare. Sadly, at the time of writing, were in a quiet part of the transmission schedules!
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