Thread: FM "deviation"
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Old 30th Mar 2010, 12:05 am   #24
Synchrodyne
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Join Date: Jan 2009
Location: Papamoa Beach, Bay of Plenty, New Zealand
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Default Re: FM "deviation"

Quote:
Originally Posted by G8HQP Dave View Post
If you don't use filters then you would have to use something like a phasing sideband receiver, but again this introduces phase shifts where you really want none. To do this you need an accurate 90 degrees over 23-53kHz, or equivalently P and P+90 in two paths, combined with an accurate P over 0-15kHz. I guess the Japs were smart enough to do this, but what about component ageing? You gain a little signal-to-noise, but potentially lose stereo separation and image clarity. My guess is that it might measure well and could have impressive advertising, but sound awful with instruments moving around for different notes. Not like other 1980's hi-fi then!
Perhaps longer-term stability was less of a problem with 1980s technology? In the HF world, I have a couple of Sony ICF2010 receivers, and a Liniplex F2 (excellent piece of equipment) that use the phasing method for sideband selection, and none seems to have suffered any deterioration over time in terms of sideband separation.

Quadrature modulation of the FM Stereo 38 kHz subcarrier was also proposed in respect of some of the various quadraphonic (or should it be tetraphonic to be homologous with stereophonic) broadcasting ideas, and also in connection with the FMX noise reduction scheme.

Cheers,
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