[BC] Mono Expands on the FM Band

[Robert Meuser]

Exactly.

This discussion was going around a few years back. I discussed it with 
Bob and he looked at as you say - in terms of the Hilbert Transform. I 
think this is where it falls apart in the real world.

R




Hershberger, Dave wrote:

>Rob Meuser writes:
>
>  
>
>>Dave
>>
>>You should discuss the vsb ssb FM stereo issue with Bob Orban 
>>as I know he has 
>>run the numbers and they are not really favorable.
>>
>>R
>>    
>>
>
>Hi Rob,
>
>I'm sorry, but I may not have been clear about what I was talking about. I
>was suggesting that a very good but non-compatible analog FM stereo system
>would place L-R on an USB subcarrier at 19 kHz. That way the L-R is farther
>down on the triangular noise spectrum of FM, and the de-emphasis is going
>the "right" direction.
>
>I have run the numbers too and here they are:
>
>Stereo penalty = 23.01 dB
>
>This is the noise penalty for GE/Zenith FM stereo - the well known 23 dB
>penalty.
>
>What if only the LSB is demodulated for L-R? This makes sense because the
>USB has a lot more noise in it than the LSB, even though the de-emphasis for
>the LSB goes in the "wrong direction" because the spectrum is inverted.
>
>Receive LSB ONLY Stereo penalty = 22.25  dB
>DB improvement over conventional demodulation by using only LSB = .76  dB
>
>These are the numbers for making a receiver that only uses the LSB at 53
>kHz, and rejects the USB. There is less than a dB to be gained by doing so
>in terms of white noise, although multipath may gain more. Not a big win.
>
>Transmit LSB ONLY Stereo penalty with LSB only receiver = 16.33  dB
>DB improvement over GE/Zenith with LSB signal and LSB receiver= 6.69  dB
>
>These are the numbers for Bill Gillman's proposal of a few years ago - to
>transmit LSB only at 38 kHz. This produces a compatible signal that works
>with existing receivers. It uses up additional deviation by modulating the Q
>channel at 38 kHz, increasing L-R energy by 3 dB, but that deviation is
>somewhat "interleaved" with the I channel. For single tone modulation there
>is no peak deviation penalty. There is no SNR advantage to existing
>receivers but special LSB only receivers have SNR improved by almost 7 dB.
>Now we're getting a noticeable improvement.
>
>And here's what I mentioned - USB at 19 kHz, impractical only because it
>wouldn't be compatible:
>
>USB ONLY Stereo penalty with USB receiver = 12.49  dB
>DB improvement with USB receiver= 10.52  dB
>
>Over 10 dB improvement in SNR! Now we're talking. Too bad it isn't
>compatible.
>
>Bob would probably point out the difficulties of audio processing for SSB
>(L-R) signals - Hilbert transforms are involved.
>
>Dave Hershberger 
>Principal Engineer 
>AXCERA
>Tel: 530-272-HDTV (4388)
>Fax: 530-272-4505 
>dhershberger at axcera.com <mailto:dhershberger at axcera.com> 
>AXCERA. Axcessing the new era of digital communications. www.axcera.com 
>960 McCourtney Road, Suite C, Grass Valley, CA 95949-7423
>
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