klopfens@bgsuvax.UUCP (Bruce Klopfenstein) (04/24/89)
I am revising an article about how the FCC misregulated AM stereo by *not* selecting a standard system. There are 3 reviewers to my article, and one doesn't seem to think stereo would have anything to do with stemming the tide of listeners to FM radio (which now has over 75% of all radio listening). He wants "proof" that stereo is superior to mono. You can laugh, but I have to answer this person's criticism. While I stated in the article that stereo gives sound presence and thought it went without saying that stereo is superior to mono, the reviewer wants more. I need help explaining why AM stereo is superior to AM mono (yes, I know AM stereo limits the distant AM signal, but my argument is that AM stereo at the very least couldn't hurt AM efforts to win back some audience). If anyone can cite any articles I could use which discuss stereo vs. mono (have any been written in the last 20 years?!?) or better still cite any AM stereo research which showed listener preferences, I'd be most grateful. If any engineers out there have any experience with AM stereo, I can cite you if you let me know who you are. The other question is, do you think the FCC should leave it to the market- place to determine technical standards? (Sony and Philips managed to work together on a standard CD format; can you imagine how much less succssful CDs would be if there were 2 or more competing standards?) What would happen if the FCC let the marketplace select an HDTV standard? Thanks, everyone. -- Dr. Bruce C. Klopfenstein | klopfens@andy.bgsu.edu Radio-TV-Film Department | klopfenstein@bgsuopie.bitnet Bowling Green $tate University | klopfens@bgsuvax.UUCP Bowling Green, OH 43403 | (419) 372-2138; 352-4818
dente@s2.uucp (Colin Dente) (04/24/89)
In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: > > >I am revising an article about how the FCC misregulated AM stereo by *not* >selecting a standard system. There are 3 reviewers to my article, and one . . . > >I need help explaining why AM stereo is superior to AM mono (yes, I know AM >stereo limits the distant AM signal, but my argument is that AM stereo at the >very least couldn't hurt AM efforts to win back some audience). > This might be a dumb question, but why should we want AM to win back some audience? - I was (and please correct me if I'm wrong) under the impression that FM gave much better sound quality, or is it just that there's more bandwidth availiable up in the MHz regions that FM usually gets broadcast at? >The other question is, do you think the FCC should leave it to the market- >place to determine technical standards? (Sony and Philips managed to >work together on a standard CD format; can you imagine how much less >succssful CDs would be if there were 2 or more competing standards?) >What would happen if the FCC let the marketplace select an HDTV standard? > Personally, I think that there really should be some sort of international legislation on things like this (just *how* irritated do Beta video owners get when they read 'VHS only' in ads for films?). The only problem is - How the hell do we get it done - with half a dozen companies & governments saying 'ours is best' what chance is there of ever finding a single solution? Perhaps it's a fundamental part of human nature, or just God's way of saying BOOGA BOOGA!! - as the saying goes... Colin =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= | Colin Dente | JANET: dente%s2@uk.ac.man.cs.ux | | Dept. of Electrical Engineering | ARPA: dente%s2%man.cs.ux@ukacrl.BITNET | | University of Manchester | UUCP: ...!mcvax!ukc!man.cs.ux!s2!dente | | England | | |-----------------------------------------------------------------------------| | ======================================================================= | =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
henry@utzoo.uucp (Henry Spencer) (04/25/89)
In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: >The other question is, do you think the FCC should leave it to the market- >place to determine technical standards? ... One problem with leaving standards to the marketplace is that in practice, this often means leaving it to the manufacturers. Believe it or not, maximizing annual profits is not the same thing as picking the best standards. In particular, manufacturers will seldom reject the idea of a standard on the grounds that it is unnecessary and silly; quite the contrary, each new standard means a new market to sell stuff to. The only major justification for AM stereo, really, is that it would sell a lot of new radios. It's a dumb idea otherwise. -- Mars in 1980s: USSR, 2 tries, | Henry Spencer at U of Toronto Zoology 2 failures; USA, 0 tries. | uunet!attcan!utzoo!henry henry@zoo.toronto.edu
klopfens@bgsuvax.UUCP (Bruce Klopfenstein) (04/25/89)
In article <1989Apr24.174150.1285@utzoo.uucp>, henry@utzoo.uucp (Henry Spencer) writes: > In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: > >The other question is, do you think the FCC should leave it to the market- > >place to determine technical standards? ... The FCC in its pro-marketplace arguments said that consumers would be able to decide which system was the best (any comments?!?) and the marketplace would allow another competitor to introduce another AM stereo system (yeah, right, as if anyone else would throw more money down a rat hole!) -- Dr. Bruce C. Klopfenstein | klopfens@andy.bgsu.edu Radio-TV-Film Department | klopfenstein@bgsuopie.bitnet Bowling Green $tate University | klopfens@bgsuvax.UUCP Bowling Green, OH 43403 | (419) 372-2138; 352-4818
ISW@cup.portal.com (Isaac S Wingfield) (04/26/89)
To satisfy your reviewer's request on why stereo is superior to mono, consider that essentially all recorded musical material these days is recorded in stereo, and is intended to be reproduced in stereo; there are fewer mono setups than ever, and so less motivation for the recording engineers to make the special compromises needed for adequate mono repeoduction. By this argument, stereo is a necessity merely to get decent sound. (One such compromise is never to allow a lead vocalist to be exactly centered on the sound stage because, while this works fine in stereo, a mono reproduction will suffer from a 3dB boost in level.) Isaac isw@cup.portal.com
klopfens@bgsuvax.UUCP (Bruce Klopfenstein) (04/26/89)
In article <17582@cup.portal.com>, ISW@cup.portal.com (Isaac S Wingfield) writes: > to mono, consider that essentially all recorded musical > material these days is recorded in stereo, and is intended to > be reproduced in stereo; there are fewer mono setups than ever, > and so less motivation for the recording engineers to make the > special compromises needed for adequate mono repeoduction. By > This is an excellent suggestion. For those of you who haven't had the "pleasure" of trying to get an academic article accepted for publication in a "scholarly" journal, anonymous reviewers (some quite pompous and condescending) ask for revisions to your original article so you can "join the club" of publishing scholars. I suspect that some of these reviewers had bad experiences in their pasts, and want to share their misery! -- Dr. Bruce C. Klopfenstein | klopfens@andy.bgsu.edu Radio-TV-Film Department | klopfenstein@bgsuopie.bitnet Bowling Green $tate University | klopfens@bgsuvax.UUCP Bowling Green, OH 43403 | (419) 372-2138; 352-4818
robert@hp-sdd.hp.com (Robert Navarro) (05/03/89)
In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: > > >He wants "proof" that stereo is superior to mono. You can laugh, but I have >to answer this person's criticism. While I stated in the article that stereo >gives sound presence and thought it went without saying that stereo is superior >to mono, the reviewer wants more. > >I need help explaining why AM stereo is superior to AM mono (yes, I know AM >stereo limits the distant AM signal, but my argument is that AM stereo at the >very least couldn't hurt AM efforts to win back some audience). > I'm not laughing at the person who asked for proof that stereo is better than mono because in one important way it's NOT. The signal to noise ratio for Stereo is lower than mono. This means the signal sounds more noisy for stereo. To see this just tune your FM radio to a station that barely comes in in stereo and then turn the stereo off. (This is why most FM receivers have the mono switch ! -- to allow weak stations to be better received.) Furthermore, AM is badly bandlimited. The baseband signal for AM is only 5KHZ! Most music requires at least twice this for decent sound reproduction. To include stereo into AM would require more bandwidth. And, unless you use single side band (which usually adds some noise in practice) the 5Khz for the baseband signal now must be divided up into two channels for stereo. Can you imagine what a 2.5Khz bandlimited signal would sound like!!!! So, while stereo AM may sound more like an original stereo music recording, it will also sound noticably noisier than mono no matter what AM stereo standard is picked. By the way, FM is better not because it is in the higher frequency ranges, but because FM is inherently a less noisy modulation scheme for radio frequencies than AM. FM does take up more bandwidth than AM but at the higher frequencies that bandwidth is availiable. So FM trades off greater bandwidth for less noise. Because of this inherent superiority, AM really doesn't stand a chance in terms of high quality (noiseless) reception. ----------------------------------------------------------------- Robert Navarro Hewlett Packard, San Diego -- Robert Navarro
dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) (05/03/89)
In article <1968@hp-sdd.hp.com>, robert@hp-sdd.hp.com (Robert Navarro) writes: > I'm not laughing at the person who asked for proof that stereo is better > than mono because in one important way it's NOT. The signal to noise > ratio for Stereo is lower than mono. This means the signal sounds more > noisy for stereo. To see this just tune your FM radio to a station that > barely comes in in stereo and then turn the stereo off. (This is why This is only true for multiplexed stereo FM. However, if you listen to stations which serve your community of license, the FM noise penalty is approximately 3 dB for stereo (because the total permissible deviation is reduced by half to accomodate the subcarrier). Multipath can exacerbate the problem somewhat; but within the primary service area (60 dBuV) a properly functioning stereo receiver should have a 3 dB noise impairment over mono. > > Furthermore, AM is badly bandlimited. The baseband signal for AM is only > 5KHZ! Most music requires at least twice this for decent sound > reproduction. To include stereo into AM would require more bandwidth. > And, unless you use single side band (which usually adds some noise > in practice) the 5Khz for the baseband signal now must be divided > up into two channels for stereo. Can you imagine what a 2.5Khz bandlimited > signal would sound like!!!! 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. Nice AM broadcasters have installed NRSC-1, the national voluntary standard which mandates a 10 kHz baseband signal with 75 uS preempasis. BTW, even crummy old C-QUAM doesn't cut the baseband audio in half...the FDMA analogy isn't true. The Kahn ISB system **does not** suffer from the problems of multipath distortion; the mono and stereo service areas are **identical**. > So, while stereo AM may sound more like an original stereo music > recording, it will also sound noticably noisier than mono > no matter what AM stereo standard is picked. 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)? If you had owned appropriate AM receivers, you would know why the Kahn ISB system is not noisier in stereo. The recovered signal to noise ratio of each sideband is exactly the same as both sidebands summed together...(think about it). If that doesn't work, consider the fact that under zero signal conditions, the output of the "phase" discriminator is zero, and the output of an "envelope" detector is whatever it was in mono. > > By the way, FM is better not because it is in the higher frequency > ranges, but because FM is inherently a less noisy modulation > scheme for radio frequencies than AM. FM does take up more bandwidth > than AM but at the higher frequencies that bandwidth is > availiable. So FM trades off greater bandwidth for less noise. > Because of this inherent superiority, AM really doesn't stand a chance > in terms of high quality (noiseless) reception. > 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! I'll concede that AM has all kinds of garbage in it whenever there is a thunderstorm, or your next door neighbour cranks up their Electrolux. Sometimes. It's not AM's fault, though it is a uniquely AM problem. An AM signal at 108 mHz with the appropriate carrier to noise ratio would be just as clean as a wasteful :-) FM channel occupying nominally 200 kHz. FM radio stations in many major markets have **severe** problems which are created by receivers and by gross short spacing. When FM was envisioned, no one ever believed that every class "C" FM would put up 100 kw and 2000 feet facilties. There are problems with three-signal intermodulation (ever been to Boston? Norfolk? Minneapolis? Charlotte?) which render 70 dBuV signals (city grade) every bit as trashy as AM stations. Where there is gross short spacing, such as exists in central North Carolina, service areas are dramatically cut, and program interruption from distant station capture is a common problem. While thunderstorms go away, a grossly short spaced FM is usually forever. AM has taken the (well deserved) rap entirely too long because of the available receivers. It is not, however, as bad as suggested. FM stereo coverage problems, short spacing, intermod, and so on are problems unique to FM, they do interrupt service and spoil reception more or less permanently. York David Anthony DataSpan, Inc
irwin@m.cs.uiuc.edu (05/04/89)
/* Written 3:41 pm May 2, 1989 by robert@hp-sdd.hp.com in m.cs.uiuc.edu:sci.electronics */ In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: >He wants "proof" that stereo is superior to mono. You can laugh, but I have >> Furthermore, AM is badly bandlimited. The baseband signal for AM is only >>5KHZ! Most music requires at least twice this for decent sound >>reproduction. To include stereo into AM would require more bandwidth. >>And, unless you use single side band (which usually adds some noise >>in practice) the 5Khz for the baseband signal now must be divided >>up into two channels for stereo. Can you imagine what a 2.5Khz bandlimited >>signal would sound like!!!! >>So, while stereo AM may sound more like an original stereo music >>recording, it will also sound noticably noisier than mono >>no matter what AM stereo standard is picked. >>Robert Navarro >>Hewlett Packard, San Diego /* End of text from m.cs.uiuc.edu:sci.electronics */ In the above, Robert indicates that AM radio is restricted to 5KHZ. The way I figure it, it is 10KHZ. On the AM broadcast band, there is a station frequency every 10KHZ, starting at 550 and going up in increments of 10 to 1600. If a station were at 760KHZ, they would have space 5 below center frequency and 5 above center frequency for their lower and upper sidebands. This is a total of 10 in width. True, each sideband is limited to 5, so, they need to used single sideband and gain 5MHZ in band width, they have the space there, it is just not being utilized to the best advantage. SSB is still AM, I wonder if the FCC would allow it? It would take several years to junk out all of the old AM receivers, maybe 25, but, they would eventually disappear, and, if you wanted the home radio to get either mode of transmission, you may be inclined to upgrade sooner, as the SSB receiver has to reinject the carrier locally, so demodulation can take place. Al Irwin irwin@m.cs.uiuc.edu
caf@omen.UUCP (Chuck Forsberg WA7KGX) (05/05/89)
In article <1968@hp-sdd.hp.com> robert@hp-sdd.hp.com.UUCP (Robert Navarro) writes:
: I'm not laughing at the person who asked for proof that stereo is better
:than mono because in one important way it's NOT. The signal to noise
:ratio for Stereo is lower than mono. This means the signal sounds more
:noisy for stereo. To see this just tune your FM radio to a station that
:barely comes in in stereo and then turn the stereo off. (This is why
:most FM receivers have the mono switch ! -- to allow weak stations to
:be better received.)
The CQUAM AM stereo system does reduce the effective listening
area due to a loss in s/n ratio and increased sensitivity to
interference. Even so, CQUAM is not as bad as FM Multiplex
stereo in terms of s/n degradation.
The Kahn independent sideband AM atereo system does not reduce
a station's coverage area, and does not suffer from CQUAM's
platform motion problem.
ISB stereo systems are also used for "power side" operation, a
signal enhancement method that places most of the audio in one of
the sidebands to give a signal to noise improvement over conventional AM.
Since only a small amount of stereo effect can be used with Power Side,
one could say that even ISB AM stereo reduces s/n compared to the
optimal mono situation, one could say stereo reduces s/n, but that's
begging the point.
Some AM stations use Kahn stereo by day and Power Side by night
when they need max s/n.
:
: Furthermore, AM is badly bandlimited. The baseband signal for AM is only
:5KHZ! Most music requires at least twice this for decent sound
:reproduction. To include stereo into AM would require more bandwidth.
:And, unless you use single side band (which usually adds some noise
:in practice) the 5Khz for the baseband signal now must be divided
:up into two channels for stereo. Can you imagine what a 2.5Khz bandlimited
:signal would sound like!!!!
Perhaps your junk radio has only 5 kHz b/w. That's not a limitation
of AM. The soon to be mandatory station filtering allows at least
a 10 kHz to 12 kHz audio freq response.
:
:So, while stereo AM may sound more like an original stereo music
:recording, it will also sound noticably noisier than mono
:no matter what AM stereo standard is picked.
Essentially wrong.robert@hp-sdd.hp.com (Robert Navarro) (05/05/89)
In article <21000021@m.cs.uiuc.edu> irwin@m.cs.uiuc.edu writes: > >/* Written 3:41 pm May 2, 1989 by robert@hp-sdd.hp.com in m.cs.uiuc.edu:sci.electronics */ >In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: >>He wants "proof" that stereo is superior to mono. You can laugh, but I have > >In the above, Robert indicates that AM radio is restricted to 5KHZ. >The way I figure it, it is 10KHZ. > >On the AM broadcast band, there is a station frequency every 10KHZ, starting >at 550 and going up in increments of 10 to 1600. If a station were at 760KHZ, >they would have space 5 below center frequency and 5 above center frequency >for their lower and upper sidebands. This is a total of 10 in width. > >True, each sideband is limited to 5, so, they need to used single sideband >and gain 5MHZ in band width, they have the space there, it is just not >being utilized to the best advantage. SSB is still AM, I wonder if the >FCC would allow it? It would take several years to junk out all of the >old AM receivers, maybe 25, but, they would eventually disappear, and, >if you wanted the home radio to get either mode of transmission, you >may be inclined to upgrade sooner, as the SSB receiver has to reinject >the carrier locally, so demodulation can take place. > I think you misunderstood me when I said that AM is restricted to 5khz. What I meant was since the space between stations was 10khz and since envelope detection is used for demodulation, each 5khz sideband of the transmitted signal is mirror image copy of the other. If the transmitted AM modutated signal is limited to 10khz, then the baseband signal is 5khz. Now, I have been told that in LA and San Diego, some stations have obtained permission to transmit a baseband signal of 10khz, but that means that they are taking up 20khz of the AM spectrum. These are probably the stations that seem to take up a large portion of the AM dial. You are correct there is a 5khz sideband above and below the center frequency, but in the current AM scheme, these sidebands contain the exact same information. SSB AM would be a much better system especially since the coherent detection required also gives a slightly better signal to noise ratio -- but the cost of the receiver is greater for coherent dectection. Modern electronics may make this cost negligible but I am not sure on that point. One of my main points about AM Stereo is that trying to fit in with the current AM scheme is going to cause some tradeoffs with AM stereo that are bound to effect it's performance or cause less bandwidth to be availiable in the AM band. Robert Navarro HP San Diego -- Robert Navarro
dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) (05/05/89)
In article <21000021@m.cs.uiuc.edu>, irwin@m.cs.uiuc.edu writes: > > /* Written 3:41 pm May 2, 1989 by robert@hp-sdd.hp.com in m.cs.uiuc.edu:sci.electronics */ > In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes: > In the above, Robert indicates that AM radio is restricted to 5KHZ. > The way I figure it, it is 10KHZ. However, the allocations plan ensures that there is at least a 20 dB carrier to carrier ratio for the first adjacent channel, not counting the tuner's rejection (assuming you are talking about the 5 mV/m city grade signal of the desired station vs. 0.5 mV/m protected contour of the next station.) In reality, the protection is much more. 10 kHz removed stations may not overlap their 500 uV/m contours. > Why not SSB? Actually, there is a product which you can buy and is street legal that is the next best thing to SSB, called a "Power-Side." This device transmits the carrier and **one** sideband using ordinary AM transmitters. The use of SSB+carrier to eliminate AM interference is at least as old as 1953 or so, when there was much work in this area. Leonard Kahn advanced this idea originally to deal with the (then unbelieveably nasty) harmonic radiation from television receiver horizontal oscillators. The local station would choose the sideband which fell between horizontal frequency harmonics. I don't know of two co-channel AM stations who have used Power-Side to eliminate interference, although there are 10 kc removed AM stations who have installed them. Since the Power-Side is essentially an STR-87 Kahn exciter with one channel muted, it is indeed type accepted and legal for use in your AM station. There is no law which says you can't transmit just the left or just the right channel. Score another round for Kahn ISB..... York David Anthony DataSpan, Inc
myers@hpfcdj.HP.COM (Bob Myers) (05/05/89)
> I'll concede that AM has all kinds of garbage in it whenever >there is a thunderstorm, or your next door neighbour cranks up their >Electrolux. Sometimes. It's not AM's fault, though it is a uniquely >AM problem. An AM signal at 108 mHz with the appropriate carrier >to noise ratio would be just as clean as a wasteful :-) FM channel >occupying nominally 200 kHz. Not to pick nits, but.... :-) David, are you saying that AM is *not* inherently more susceptible to noise ("static", etc.) than FM? Ever try AM vs NBFM on 10 meters? (Assuming a decent FM detector, of course.) Certainly, AM can be clear as a bell given the "appropriate carrier to noise ratio", but for equal power transmitters located similar distances from my receiver, I believe FM has at least a small advantage as far as noise rejection. The "capture effect" of FM is also a nice feature in most instances, as the listeners are not plagued with the heterodyning that you usually have to put up with on the AM band at night. (Although admittedly, moving AM broadcast to a much higher frequency band, one not usually subject to long-range propagation, would help muchly here!) One other item - and this is really getting picky, but what the hell - I really don't think that either an AM or an FM signal would do particularly well with a 108 milliHertz carrier, do you? (Add several :-)s here) > AM has taken the (well deserved) rap entirely too long >because of the available receivers. It is not, however, as bad >as suggested. FM stereo coverage problems, short spacing, intermod, >and so on are problems unique to FM, they do interrupt service and >spoil reception more or less permanently. ....but no argument here whatsoever! Bob Myers KC0EW HP Graphics Tech. Div.| Opinions expressed here are not Ft. Collins, Colorado | those of my employer or any other {the known universe}!hplabs!hpfcla!myers | sentient life-form on this planet.
robert@hp-sdd.hp.com (Robert Navarro) (05/05/89)
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
ISW@cup.portal.com (Isaac S Wingfield) (05/05/89)
York David Anthony writes: >the FM noise penalty is >approximately 3 dB for stereo (because the total permissible deviation is >reduced by half to accomodate the subcarrier). It's been a long time, but I believe the SNR penalty for stereo is about 30dB (29.7 is what comes to mind), and it's not because the deviation is reduced (it's not), but because the noise bandwidth is 53kHz instead of 15kHz. He's right about multipath being much worse. Isaac isw@cup.portal.com
kanner@Apple.COM (Herbert Kanner) (05/05/89)
>>On the AM broadcast band, there is a station frequency every 10KHZ, starting >>at 550 and going up in increments of 10 to 1600. If a station were at 760KHZ, >>they would have space 5 below center frequency and 5 above center frequency >>for their lower and upper sidebands. This is a total of 10 in width. >>True, each sideband is limited to 5, so, they need to used single sideband >>and gain 5MHZ in band width, they have the space there, it is just not >>being utilized to the best advantage. SSB is still AM, I wonder if the >>FCC would allow it? It would take several years to junk out all of the >>old AM receivers, maybe 25, but, they would eventually disappear, and, >>if you wanted the home radio to get either mode of transmission, you >>may be inclined to upgrade sooner, as the SSB receiver has to reinject >>the carrier locally, so demodulation can take place. >> > I think you misunderstood me when I said that AM is restricted to 5khz. >What I meant was since the space between stations was 10khz and since >envelope detection is used for demodulation, each 5khz sideband of the >transmitted signal is mirror image copy of the other. If the transmitted >AM modutated signal is limited to 10khz, then the baseband signal is >5khz. Now, I have been told that in LA and San Diego, some stations have >obtained permission to transmit a baseband signal of 10khz, but that >means that they are taking up 20khz of the AM spectrum. These are >probably the stations that seem to take up a large portion of the AM dial. > >You are correct there is a 5khz sideband above and below the center >frequency, but in the current AM scheme, these sidebands contain the >exact same information. SSB AM would be a much better system >especially since the coherent detection required also gives a slightly >better signal to noise ratio -- but the cost of the receiver is greater >for coherent dectection. Modern electronics may make this cost negligible >but I am not sure on that point. I don't believe SSB would be practical for music, although we know from practical experience that it is acceptable for speech. The reason is that music puts very strict requirements on frequency ratios. Consider a note from a musical instrument. With rare exceptions, which technically are called 'noise' (e.g. a sound from a vibrating circular membrane without benefit of a resonator: a bass drum, but not a tympani), all musical sounds have harmonics which are exact integral multiples of the fundamental frequency. Now, if you are receiving SSB and the injected frequency is not spot on, you will disturb this integral relationship. For example, consider a 400 herz note with a second harmonic at 800 herz. Now, if we have a 1 megaherz carrier and consider upper sideband, the fundamental will be 1,000,400 herz and the second harmonic will be 1,000,800 herz. Now make the signal a SSB signal. The carrier goes away. Back at my receiver, I inject a carrier that is off by one hundreth of a percent, namely 1,000,100 herz. Now, the two frequencies which I will detect will be 300 herz and 700 herz; the upper note is about 14% too sharp to be a second harmonic of the lower note. To understand what 14% means: a musical half-step is a frequency change of about 6%. -- Herb Kanner Apple Computer, Inc. {idi,nsc}!apple!kanner kanner@apple.com
dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) (05/08/89)
In article <1666@internal.Apple.COM>, kanner@Apple.COM (Herbert Kanner) writes: > >>On the AM broadcast band, there is a station frequency every 10KHZ, starting > >>at 550 and going up in increments of 10 to 1600. If a station were at 760KHZ, > >>they would have space 5 below center frequency and 5 above center frequency > >>for their lower and upper sidebands. This is a total of 10 in width. > >>True, each sideband is limited to 5, so, they need to used single sideband > >>and gain 5MHZ in band width, they have the space there, it is just not Oh, good grief, people !!!!!!! Simply because the AM channel spacing is defined as 10 kHz does not mean that the permissable occupied bandwidth is 10 kHz. AM radio stations are never allocated to the same community 10 kHz apart for a variety of reasons, the least of which would be the horrendous 10 kHz whistle which would result from the two carriers beating in the receiver front end. Back when AM stations were required to do audio proofs of performance, there was a specification for amplitude and distortion at 7500 Hz. Since this regulation is almost as old as Moses, we can properly conclude that not only was a baseband of 5 kHz not desirable, but flat out illegal. (The measurement is to be taken from the main studio microphone and read on the station's modulation monitor.) How do we reconcile this problem? The FCC obviously expects you to have at least 7500 Hz audio bandwidth, but the channels are 10 kHz apart!!! Simple, don't allot adjacent channel stations to anywhere near the same service area. Very simply: The protected co-channel interference free contour is 500 uV/m. The FCC defines adjacent channel stations causing objectionable interference if the 500 uV/m contour of the adjacent channel overlaps the 500 uV/m contour of the desired channel (1:1 carrier to carrier ratio). The primary service area of an AM station is 5 mV/m. This is the signal a station licensed to a community must place over that community. So, at the city grade contour, the carrier to carrier ratio is at least 20 dB. In reality, since the 0.5 mV/m contour of the offending station attenuates rapidly with distance, and since the 0.5 mV/m contour of the offending station can't breach the 0.5 mV/m contour of the desired station, the carrier to carrier suppression is more like 40 - 50 dB at the 5 mV/m contour of the desired station. I just took WOGR off the air this morning for a few seconds and took a casual measurement: WOGR (in the parking lot) 5.2 mV/m WBSC 1550 kHz, Bennettsville, S.C. 0.031 mV/m WCKY 1530 kHz, Cincinnati, Ohio 0.012 mV/m D/U ratio, WOGR to WBSC: 44.5 dB D/U ratio, WOGR to WCKY: 52.7 dB A 10 kc audio notch is more than adequate to remove the whistle, if one were to drive down to between WOGR and WBSC to hear it (it's about 50 miles from where I sit). With WOGR off the air, the sidebands from WBSC and WCKY are inaudible. With WOGR on the air, you can't hear a 10 kHz whistle. Now, 40-50 dB of carrier suppression is not exactly high fidelity compared to your local CD player, but is certainly beyond adequate for many entertainment and information uses. As for SSB in the home, forget this. AM phase rotation with conventional signals is bad enough, but at least the receiver has a carrier which has hopefully been rotated about the same amount as the sidebands. With SSB, the reference is lost (obviously), so when the sidebands' "carrier phase" change, the receiver's carrier phase didn't track it. SSB is bloody hard enough to tune in on my Drake R4, and a precision synthesizer to the nearest 0.1 Hz or so is not the kind of thing I want to take to the beach or ball-park. We do have the next best thing, though, "Power-Side", explained in previous articles. Perhaps I've been way too harsh on the FM advocates here, but the practical implementation of AM does not have to be so bad that there is not parity within the same order of magnitude. My hackles get up when people who should know better state that "The bandwidth of an AM signal is 5 kHz." Even worse is the still slow adoption of NRSC-1 compliant receivers (even the (*&%*(% Becker which comes in new Mercedes still sounds like a telephone on AM, but at least you can side tune with it...on the other hand, the Delco-GM high end Caddy radio is excellent, as is the one which comes in the Toyota Supra). We have FM stations here with about a 10 dB dynamic range, so what good is a 70 dB signal to noise ratio to your average listener? There has got to be someone on this Net who has heard or owns a wideband AM tuner. If not, go down to your local Sparkomatic dealer (that's right, Spark-o-matic) and ask to see the DIN-mount SR430. This is a current model chassis with the "AM wide button." Tune in a decent station, and push the button. Hearing is believeing. York David Anthony DataSpan, Inc P.S. I am not endorsing Sparkomatic here.
aj-mberg@dasys1.UUCP (Micha Berger) (05/14/89)
Actually, FM is inherently less noisy. I remember that much from my communications course. Let's see if I can remember how. In AM, the noise is basically the noise-spectral-density integrated over the area around the carrier frequency. Thus, the wider the txmission bandwidth, the more noise. In FM, increasing the modulation index increases the bandwidth, but lowers the signal to noise ratio. The FM differs from AM (100% modulated AM, of same output power) in signal to noise ratio by a factor of 3B^2 where B is the modulation index (delta f / carrier f). -- Micha Berger -------------------------------------v------------------------------------------"The world stands on three things: on| AishDas Society / Aspaklaria Publicationsthe Torah, on Service [to the L-rd], | 73-32 173 St, Hillcrest, NY 11366 and on Acts of Kindness" | (718) 380 - 7572 - Shimon the Righteous, Avos 1:2 | email: ...cmcl1!dasys!aj-mberg -------------------------------------^------------------------------------------