Dear Andy, LF group,
At 13:45 01/07/2003 +0100, you wrote:
RU Sure ???
The RA1792 (the following model from the 1772 perhaps) displays the actual
frequency at the middle of the filter passband, then generates an audio
Yes - well, it certainly is on mine anyway... The 1772 predates
microcontrollers, and is completely different in design from the 1792,
although some parts have clearly been cribbed for the later design. Racal
have opted for a fixed BFO frequency in all modes centered at the 1.4MHz IF
centre frequency, with separate USB and LSB filters for SSB/ISB. CW
reception is actually in USB mode, with narrower filters with passband
centres offset by 1kHz from the BFO frequency... whatever mode you select,
the displayed frequency is the one at which the input signal will be
zero-beat with the BFO, and so outside the filter passband with narrow
bandwidths. The display board has buckets of TTL and stuff - I expect the
designers thought correcting the display for different modes was too much
trouble. But so you are not stuck with a fixed 1kHz audio tone, they
provided a rather drifty variable analogue BFO as well. A little
idiosyncratic, you might say!
Cheers, Jim Moritz
73 de M0BMU
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