Here is a link to the RBDS standard: ftp://ftp.rds.org.uk/pub/acrobat/rbds1998.pdf
And another link to the digital AM radio standard: http://www.ibiquity.com/technology/pdf/Waveforms_AM.pdf On Tue, 14 Feb 2006, Robert McGwier wrote: > Al, Matt: > > Thanks for your input. I am pretty ignorant about these FM standards > and basically I googled my way to a reasonable spec, drew the flow > graph and coded it. The stereo demux was definitely not working with > DEemphasis applied to the composite signal. And it was clear why. The > taper was awful and the lower sideband was approximately 10 dB higher > than the USB on the L-R, DSBSC stereo signal. I removed the deemphasis > and voila, stereo. That said, when the pilot/carrier is 20 dB out of > the noise in the 512 pt FFT, that should be strong enough that you do > 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. > > I hate this RDS Top Secret MONEYWORD specification. Frank and I are > determined to fix their wagon. > > I did not know about Achilleas work. I will search the archive. > > Bob > > > > al davis wrote: > > On Monday 13 February 2006 20:06, Matt Ettus wrote: > > > >> I seem to remember that the preemphasis on stereo signals is > >> not performed on the multiplexed signal. It is actually > >> performed on the audio components separately, before mixing > >> with the stereo subcarrier. Therefore deemphasis needs to be > >> done after the stereo part is mixed back down to baseband. > >> > >> To me, this is backwards, and is not useful, but I think that > >> is the standard. Achilleas sent an email to the list several > >> months ago on this subject. He also had a simple > >> implementation that did stereo. > >> > > > > Actually it is very useful the way it is. It would be bad to > > preemphasize the composite signal. > > > > To preemphasize the composite in effect converts the system to > > phase modulation. The subcarrier would then consume most of > > the bandwidth, and the baseband (mono) would be drastically > > reduced, resulting in a significant reduction in apparent mono > > signal to noise ratio. Stereo signal to noise ratio would be > > about the same as it is now, but there would be no advantage to > > mono. > > > > In the existing system, if stereo SNR is not good enough, you > > can switch to mono and get almost as good SNR as if stereo > > wasn't there. "Almost" means about a 6 db degradation, which > > is due to the fact that baseband modulation must be lowered by > > that much. > > > > > > _______________________________________________ > > Discuss-gnuradio mailing list > > Discuss-gnuradio@gnu.org > > http://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > > > > > > _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio