Re: [Discuss-gnuradio] Stereo gain "hacked"

[Lamar Owen]

On Tuesday 14 February 2006 00:13, Robert McGwier wrote:
> Thanks for your input.  I am pretty ignorant about these FM standards
[snip]
> not have hiss that is irritating.  But the COMPOSITE signal is what is
> FM modulated but I bet they do not preemphasize the composite signal.
> They might do preemphasis on the L+R baseband signal as Matt suggests
> but I just don't know about the others.  I am trying to understand what
> about that would make sense.  It would be very interesting to read a
> real spec.  I have googled and not really found one a  useful one.

For the actual transmitter-side specs, the FCC rules are the starting point, 
specifically Title 47 of the Code of Federal Regulations (47 CFR), part 73.  
Look at 47CFR73.310 (definitions), 317 (permissible transmissions, including 
the preemph clause), 319 (subcarriers in general), and 322 (stereo) (see 333 
for the charts and curves used as standards): Links: 
http://www.hallikainen.com/FccRules/2006/73/310/ 
http://www.hallikainen.com/FccRules/2006/73/317/ 
http://www.hallikainen.com/FccRules/2006/73/319/
 http://www.hallikainen.com/FccRules/2006/73/322/  and for 47CFR73.333 go to 
http://www.access.gpo.gov/nara/cfr/waisidx_05/47cfr73_05.html and click on 
the PDF for 73.333, so you can get the figures).

What this doesn't get you is the pre-transmitter signal chain; the Orban 
Optimod 8100 manual is a great resource for this; see the directory at 
ftp://ftp.orban.com/8100A1

The Manual Section 1-3 PDF in that directory has a block diagram and a theory 
of operation section that shows how the  grandaddy of all 'Industry Standard' 
FM processors does stereo.  Both L+R and L-R get preemphasis, but preemphasis 
is not applied to the composite signal.

(I have been a broadcast engineer for 16 years, ten of which were on a full 
time basis).
-- 
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu