Thread: ISB Receivers
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Old 18th Apr 2016, 1:56 am   #31
Synchrodyne
Nonode
 
Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
Posts: 2,943
Default Re: ISB Receivers

I have found a little more information on the Redifon R408, attached. That confirms that it was conceived as a marine HF receiver, but ended up as being suitable for use as a general purpose communications receiver.

The IF bandwidth was continuously variable from ±8 kHz to ±800 Hz, with half that said to be available for SSB operation, either LSB or USB. I’d assume that the basic variation was symmetrical about the final IF of 80 kHz. So in the SSB case, given that it was said that retuning was not needed when switching between sidebands, it looks as if the bandwidth range was either between 800 Hz and 8 kHz below 80 kHz, or 800 Hz to 8 kHz above 80 kHz. That then leads to the question as to was SSB sideband separation done with filters – one each for USB and LSB – that followed the main IF filters, in which case the emphasis would have been on carrier (IF) side cutoff, given that the outer cutoff was done by the main IF filters, or was it done in the AF domain by phase-shifting and matrixing (as I think was developed by Norgaard of GE and first used on the GE YRS-1 SSB adaptor). Whichever way it was done, the write-up included the comment: “In practice, during reception of i.s.b. transmissions containing teleprinter information in one sideband and audio information in the other, use of the sideband switching facility to listen to audio has completely eliminated any break through from the teleprinter intelligence, and vice versa.”
Cheers,
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