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 _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio