Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!ucsd!sdcsvax!ucsdhub!hp-sdd!robert From: robert@hp-sdd.hp.com (Robert Navarro) Newsgroups: sci.electronics Subject: Re: Stereo vs. Mono: Q about AM Stereo Keywords: AM,radio,stereo,mono,FCC Message-ID: <1973@hp-sdd.hp.com> Date: 4 May 89 19:49:42 GMT References: <4046@bgsuvax.UUCP> <1968@hp-sdd.hp.com> <1480@unccvax.UUCP> Sender: news@hp-sdd.hp.com Reply-To: robert@hp-sdd.hp.com.UUCP (Robert Navarro) Organization: Hewlett-Packard, San Diego Division Lines: 81 In article <1480@unccvax.UUCP> dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) writes: >In article <1968@hp-sdd.hp.com>, robert@hp-sdd.hp.com (Robert Navarro) writes: > No, no, no, no, no, no, no. > > The baseband signal is **not** limited to 5 kHz. Where do people >get this stuff (and we AM broadcasters wonder why the band is deteriorating). >There are AM **receivers** which are bandlimited to 5 kHz; but the fidelity >limit (twice the bandwidth, by your own emissions) generally is unlimited >within the service area. Maybe they have changed the FCC standards lately, I'm not sure. But the according to everyone I've talked to at work and a professor at San Diego State in communication electronics the bandwith for commercial AM is 10KHZ. If a broadcaster is within this limit, then their is only 5khz worth of signal information in the receieved 10khz signal since the two sidebands are mirror image duplicates of each other in commercial AM. Also "Reference Data for Radio Engineers", Howard Sams Inc. 1979 states on page 30-1, "Standard-broadcast stations are licensec for operation on channels spaced by 10 kilohertz and occpying the band from 535 to 1605 kilohertz." Admittedly, this does not limit the bandwidth of a station to 10khz (other FCC regulations may though, but I don't have a copy of the regulations on hand.) it only means that channels are assigned in 10khz increments. Now, that means that to avoid interference stations should only have a bandwith of 10khz. A station may broadcast a signal with bandwidth greater than 10khz, but they better talk to the FCC and make sure there are no nearby stations or there's going to be some major interference. I'm really not sure what you mean by "the fidelity limit generally is unlimited within the service area." But since the Random House College Dictionary defines fidelity as the ability to receive electronic signals accurately, I would say that either your not using AM as your modulation scheme or you have unlimited carrier power within your service area. (Maybe you also use AM radio to power your house like in Tesla's power distrubution scheme.) > Nice AM broadcasters have installed NRSC-1, the national voluntary >standard which mandates a 10 kHz baseband signal with 75 uS preempasis. > 10khz baseband doesn't sound bad, but it's not quite high fidelity. > > Do you own an AM stereo receiver? Do you live in a market >which has radio stations using the Kahn ISB system? Do you own an >NRSC-1 compliant receiver (with 10 kc bandwidth and deemphasis)? I'm really not all that interested in owning AM stereo as long as it is a system that is built to be backward compatible with mono AM. To make a really good system you'd have to trash the current AM setup and start over again (probably at a higher frequency range and using SSB) > > If you had owned appropriate AM receivers, you would know >why the Kahn ISB system is not noisier in stereo. I don't own the system nor do I know it's setup -- so no comment. > Say **what**? > FM is not inherently a less noisy modulation scheme than >AM. What do you think the FM stereo subcarrier is...suppressed >carrier, double sideband AM! > The fact that the FM subcarrier L-R signal is modulated to 38 khz using DSB-SC does not greatly effect the transmitted FM signal's noise immunity. Most of the noise corrupting an RF signal currupts it's amplitude the frequency is much harder to corrupt. In FM systems the first thing they do is hard limit the signal, therby eliminating all AM varations in signal and hence most of the noise associated with AM. Only after the signal is recieved in FM and demodulated into a compostite baseband signal with the L-R channel at 38khz is the the L-R channel demodulated. But since this signal is derived from a signal received and demodulated in FM it will not suffer from the noise effects that a normal AM signal would suffer from. There's a lot math that I went through years ago to show that FM is better that AM. If I have time , maybe I'll look it up later at post it. Till then read a good book on communication systems to see more on why FM is better than AM. Robert Navarro Hewlett Packard San Diego Division. -- Robert Navarro