glen herrmannsfeldt wrote:> Jerry Avins wrote: > >> sheepshaggerx@yahoo.co.uk wrote: >> >>> My application is in software radio so that the signal will have a >>> spectrum (random) anything up to say 15kHz for a normal FM stereo >>> radio. I use the sine wave as an example as we normally test systems on >>> sine waves and sweep them to do a freq response. > > >> Broadcast FM has a carrier deviation of 150 KHz in a channel 200 KHz >> wide. > > > I thought it was 75kHz, but it is plus or minus 75kHz so the bandwidth > is (approximately) 150kHz.75 is for Television. Sheepshagger is off by a factor of 10. In the US, AM channels are at least 10 KHz wide; some used to be 30. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
I-Q vs PLLs
Started by ●June 7, 2005
Reply by ●June 8, 20052005-06-08
Reply by ●June 8, 20052005-06-08
"glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message news:8IqdnQDbEueQ8zrfRVn-rg@comcast.com...> Jerry Avins wrote: > > > sheepshaggerx@yahoo.co.uk wrote: > > > >> My application is in software radio so that the signal will have a > >> spectrum (random) anything up to say 15kHz for a normal FM stereo > >> radio. I use the sine wave as an example as we normally test systems on > >> sine waves and sweep them to do a freq response. > > > Broadcast FM has a carrier deviation of 150 KHz in a channel 200 KHzwide.> >Thats the modulation depth -not the modulating freq. Rimmer
Reply by ●June 8, 20052005-06-08
"Jerry Avins" <jya@ieee.org> wrote in message news:dZWdnfYyaMl_DjrfRVn-vQ@rcn.net...> glen herrmannsfeldt wrote: > > Jerry Avins wrote: > > > >> sheepshaggerx@yahoo.co.uk wrote: > >> > >>> My application is in software radio so that the signal will have a > >>> spectrum (random) anything up to say 15kHz for a normal FM stereo > >>> radio. I use the sine wave as an example as we normally test systemson> >>> sine waves and sweep them to do a freq response. > > > > > >> Broadcast FM has a carrier deviation of 150 KHz in a channel 200 KHz > >> wide. > > > > > > I thought it was 75kHz, but it is plus or minus 75kHz so the bandwidth > > is (approximately) 150kHz. > > 75 is for Television. Sheepshagger is off by a factor of 10. In the US, > AM channels are at least 10 KHz wide; some used to be 30. > >You are confusing depth of modulation and modulating freq. The mod freq goes up to 15kHz and the depth of modulation is 100kHz. The ratio of the two gives beta the FM modulation index. Sounds to me that this is something overlooked by the digital boys - comparison with a simple PLL.They never were much good at closing loops. Rimmer
Reply by ●June 9, 20052005-06-09
Rimmer wrote:> "Jerry Avins" <jya@ieee.org> wrote in message > news:dZWdnfYyaMl_DjrfRVn-vQ@rcn.net... > >>glen herrmannsfeldt wrote: >> >>>Jerry Avins wrote: >>> >>> >>>>sheepshaggerx@yahoo.co.uk wrote: >>>> >>>> >>>>>My application is in software radio so that the signal will have a >>>>>spectrum (random) anything up to say 15kHz for a normal FM stereo >>>>>radio. I use the sine wave as an example as we normally test systems > > on > >>>>>sine waves and sweep them to do a freq response. >>> >>> >>>>Broadcast FM has a carrier deviation of 150 KHz in a channel 200 KHz >>>>wide. >>> >>> >>>I thought it was 75kHz, but it is plus or minus 75kHz so the bandwidth >>>is (approximately) 150kHz. >> >>75 is for Television. Sheepshagger is off by a factor of 10. In the US, >>AM channels are at least 10 KHz wide; some used to be 30. >> >> > > You are confusing depth of modulation and modulating freq. The mod freq goes > up to 15kHz and the depth of modulation is 100kHz. The ratio of the two > gives beta the FM modulation index. > Sounds to me that this is something overlooked by the digital boys - > comparison with a simple PLL.They never were much good at closing loops.Who, me? I know the difference. The actual carrier swing is 100 kHz, but sidebands extend the sum signal width to 150 kHz, The channels are 200 KHz apart. Generally, the highest modulating frequency is 15 kHz. US and UK preemphasis have different time constants. These numbers are modified for stereo and SCA. Any broadcast FM detector that the OP builds should accommodate stereo and perhaps SCA too. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 9, 20052005-06-09
Rimmer wrote:> "glen herrmannsfeldt" <gah@ugcs.caltech.edu> wrote in message > news:8IqdnQDbEueQ8zrfRVn-rg@comcast.com... > >>Jerry Avins wrote: >> >> >>>sheepshaggerx@yahoo.co.uk wrote: >>> >>> >>>>My application is in software radio so that the signal will have a >>>>spectrum (random) anything up to say 15kHz for a normal FM stereo >>>>radio. I use the sine wave as an example as we normally test systems on >>>>sine waves and sweep them to do a freq response. >> >>>Broadcast FM has a carrier deviation of 150 KHz in a channel 200 KHz > > wide. > >> > Thats the modulation depth -not the modulating freq.The audio has a spectrum of 15 KHz; the FM signal, 150. It's the 150 that needs to be demodulated. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●June 10, 20052005-06-10
Jerry Avins wrote: *snip)> Who, me? I know the difference. The actual carrier swing is 100 kHz, but > sidebands extend the sum signal width to 150 kHz, The channels are 200 > KHz apart. Generally, the highest modulating frequency is 15 kHz. US and > UK preemphasis have different time constants. These numbers are modified > for stereo and SCA. Any broadcast FM detector that the OP builds should > accommodate stereo and perhaps SCA too.The distinction I was originally trying to make was between amplitude and peak-to-peak. As far as I know, FM is normally described as amplitude of deviation, that is, plus or minus from the carrier frequency, http://www.fcc.gov/mb/audio/subcarriers/ but a web search found plenty of web sites giving the peak-to-peak value. Television sound, at least in the US (and probably other NTSC countries) is FM with 25kHz deviation amplitude. Some FM receivers will tune down to the channel 6 sound frequency, which will be somewhat quieter than a normal FM station. http://edocket.access.gpo.gov/cfr_2004/octqtr/47cfr73.681.htm Broadcast FM has a 75kHz deviation amplitude, or 150kHz p-p. Unlike AM where the side bands are a simple function of the modulating signal FM sidebands go to infinity even with a modulating sine wave. Broadcast FM signals may have a 38kHz DSB/SC stereo subcarrier and also a 67kHz FM SCA subcarrier, and possibly other subcarriers. The actual bandwidth used is then a complicated function of the modulation frequencies and amplitudes. In addition, it seems that according the the fcc.gov site above, FM stations with subcarriers are allowed up to 110% modulation (relative to the +/- 75kHz) total. -- glen
