Building a radio station requires many choices to be made. The antenna design, the grounding scheme, the audio system, to name several. Let’s look at audio.
Building a radio station requires many choices to be made. The antenna design, the grounding scheme, the audio system, to name several. Let’s look at audio.
The audio network within a radio station is not a simple plug and play sort of thing, it involves complex architectural considerations, i.e., balanced or unbalanced lines, line level matching, mixing, patching, equalizing, signal processing, and stereo/monaural. We will focus on the stereo-mono subject.
CD recordings and many downloaded audiofiles arrive as stereophonic source material, and some audiofiles arrive in mono form. Original studio recordings made by the radio station must be captured one way or the other, at the choice of the recording engineer. Finally, the transmitter will dictate the ultimate product as either stereo or mono.
The leading advocate for stereophonic AM is RFBurns whose KROCKS specializes in AM stereo. At the same time, Carl Blare (me) is sold on mono radio, and that’s where this discussion heats up.
My station, KDX Worldround Radio, is mostly talk, so let’s look at the human voice. The human voice is what? It is a monaural instrument. When I see double-capsule stereo lapel mics pinned onto a performer I already know that the engineering policy is ignorant of the fact that the voice, already mono, will suffer from some phase-cancelation when those two capsules are mixed down to mono. The clearest and most distinct reproduction of a human voice can only be done in mono with a single microphone.
Even music features any number of monaural instruments…. and by instruments I am talking about acoustic “natural” instruments, not electronic “artificial” instruments, which are nothing more than P.A. systems driving loudspeakers and already present in electronic form right into an input plug – no mics needed.
A clarinet is a monaural instrument.
A trumpet is a monaural instrument.
A bass is a monaural instrument.
Each piece in a drum set is a monaural instrument.
What is stereo? Stereo is the acoustic sense of space in between the various instruments in an orchestra and the reverberation of the concert hall. It makes a group performance more natural and quite pleasant, when well recorded. But even the best stereo recording must mix-down clearly to a monaural version for the portable radio listener who is hearing an L+R mixdown (left+right=mono).
An ideal broadcast plant would be capable of perfect mono during spoken voice portions and musical solos, with a fade-over to stereophonic sound for orchestral events or sports crowd ambiance.
But the technology, as I understand it, is presently an either-or proposition – either mono or stereo, not inter-mixable. That limitation applies to online streaming, and AM/FM technology. In FM the sub-carrier generators required for stereo actually detract from the stability of mono reception, especially on the outer fringe area of the station signal.
In webcasting a stereo stream occupies more bandwidth per listener which has its own trade-offs.
The bottom line for KDX is that mono = clear talk quality and robust music quality, with the slight disadvantage that the spacial effect is not present for ensemble music. If we were a music station it would be the other way around.
part 15.219 forget am stereo,
part 15.219 forget am stereo, not going to work properly. antenna system has too high a “Q”.
AM Stereo is well suited under part 15.209 or 221.
but count on you being the only real listener as not much of the public has cquam receivers.
so basically it would be for your own listening pleasure.
for part 15 FM always run mono unless you have access to leaky coax setup.
Why?
Why would C-QUAM not work properly on a 3 meter stick?
Mine works just fine. AM stereo does not rely on a sub carrier like FM does for transmitting the L-R audio. It relies on quadrature modulation of the envelope 90* in relation to the L+R.
Switching between a mono TX and a C-QUAM TX on my 3 meter system each resulted in the same coverage and the C-QUAM unit sounded better on a mono receiver than did the mono TX.
My 3 meter antenna consists of a 1/2 inch diameter copper pipe with a 86 turn loading coil and peaking capacitor, all mounted inside the WX proof box mounted on a short pole 1 meter off the ground. Ground system consists of 20 10 foot long radials and ground rods.
Nothing fancy there in the antenna system. In fact I did nothing special to the antenna system when I swapped out the mono TX with the C-QUAM TX, other than re-peaking the tuning cap by a slight turn.
RFB
something to do with the
something to do with the phase modulated stereo signal and the very narrow bandwidth of the electrically short radiator
Do What?
“something to do with the phase modulated stereo signal and the very narrow bandwidth of the electrically short radiator”
Well the short radiator has nothing to do with the modulation method of the carrier being transmitted. The signal occupies no more bandwidth than a standard 10Khz channel allotment.
The radiator also has nothing to do with how the envelope is modulated in phase either, again taking place within the standard 10Khz AM channel.
But if your concerned about radiator bandwidth capability, simply use a fatter radiator! 😀
RFB
Getting It
This is Carl Blare, and I think I get it.
IF you broad-chase…. I mean, broadcast in C-QUAM, your audience will be able to listen in EITHER mono or stereo on an AM radio. That seems like an ideal situation for AM broadcast.
The problem with FM broadcast is compounded by the fact that
(A) Stereo listeners outside the prime signal area will only hear noise;
(B) Mono listeners outside of the prime signal area will only hear noise.
Therefore AM Stereo is superior to FM stereo.
Address all questions to this website.
A vote for FM stereo
I’ve chosen to broadcast a Pt. 15 signal in FM stereo, since I’m a music station. Biggest problem is with home stereo systems that don’t automatically switch to mono until the noise level is sky high. In that case, the listener has to manually select the mono mode (or “mpx mode off”) on their receiver to listen without the noise. Most car radios, and portables, I’ve discovered, do a pretty good job of automatically switching to mono before the noise level becomes objectionable. The switch is almost seamless.
After the automatic switch is made in the receiver, does a mono station really go farther than a stereo station? My testing says “Yes, but only marginally.” I would much rather have my listeners who are close enough to enjoy the stereo to be able to do so, rather than go mono for the little bit of extra range. In my testing it wasn’t much…maybe 10% at the most. And stereo sounds SO GOOD!
Also, don’t forget that many scanning curcuits on receivers use the 19khz stereo pilots to tell the radio to stop scanning, and listen. If a potential listener hits “scan” on their radio, and you’re broadcasting in mono, the scanner won’t stop and your station will be passed up, even if the signal is strong, and bye-bye potential listener!
Marginal Measurement
While its true that a mono FM transmission may seem to go farther than its stereo counterpart, it really doesn’t all that much. Marginal is an understatement.
PILOT LEVEL 101.
The 19 Khz pilot level is nothing more than a high pitched audio tone at 19Khz, injected into the audio path in the exciter, normally set for 10 percent modulation. At 10 percent modulation, it robs 10 percent of the total amplification factor in the TX’s final TPO (Total Power Output).
So trying to get a precise account for how much distance that reduces the already limited signal range..well is marginal and a waste of time trying to measure it and really doesn’t matter at that point as most receivers will shut over to mono at a certain signal to noise ratio anyway, throwing off the measurement.
One of those fancy dancy Potomac’s are required to actually get any accuracy in determining just how little effect it does have with a 19Khz pilot or not.
What is more ironic..is a lot of people are using transmitters that do not have any sort of adjustment pot for the 19Khz pilot level or even the 38Khz null…all pre-set and more likely not even set the way they should be…yes even in those sporting the…how did Carl put it…Eff Cee Cee…ya that’s it…the Eff Cee Cee number.
If you do disable the 38 and 19 Khz and notice a HUGE increase in range, then both of those were improperly set and set way too high..so your better off in the mono world.
AM stereo does not suffer from such nonsense.
Ha Ha.
😛
RFB
I Thought So As Well At One Point
“count on you being the only real listener as not much of the public has cquam receivers.”
After spending the time and money to implement C-QUAM I also thought who will be able to listen to this wonderful stereo sound from the AM radio.
Well I suddenly realized that this is not 1980 anymore. It is the 21st century where there is a market saturated with HD radios, most capable of decoding C-QUAM! And after that, I put away the worry about me being the only one enjoying AM Stereo.
A few months later I had learned that someone out there was spreading the word about my C-QUAM station and soon after that, I got letters and emails thanking me for having an AM Stereo station. I suspect these folks either are tuned in via an HD radio, or have the better vintage AM stereo radios who’s stereo light has not turned on in ages.
RFB
I Agree With RFB
I Agree with RFB the coverage on a 3 meter stick and with proper grounding, your coverage should do just fine with c-quam stereo,
sooner or later i will make a blog all about am stereo and its functions.
But As
But as I think about it some more, here’s what I want for AM, FM, everything……
When there is one voice speaking I want the whole system to revert to monaural mode. This would mean 1-audio track, not stereo, running through the Player software.
It would mean the AM transmitter would send a 100% in-phase perfectly focused voice-mono-signal. I gather that the C-QUAM already allows that situation to be true.
It would mean the FM transmitter would make a “soft-switch” into mono mode so the voice carries as far as possible on the carrier without the subcarrier junk.
It would mean the stream would switch down to reduced bandwidth to conserve space on the internet connection.
BUT as soon as musical material appeared or sporting action, the whole system would smoothly open into a stereo panorama and it would be the best of both worlds.
IF I can have that for Christmas, I’ll forget about the electric train.
VBR
“the stream would switch down to reduced bandwidth to conserve space on the internet connection.”
Variable Bit Rate streaming allows this.
An elaborate idea to bounce back and forth dependent upon program source..not sure if Santa’s elves has enough time to build such a system in time for Xmas!
“It would mean the AM transmitter would send a 100% in-phase perfectly focused voice-mono-signal. I gather that the C-QUAM already allows that situation to be true.”
C-QUAM constantly sends out the perfectly focused mono signals all the time, regardless if the 90* phased L-R envelope lobes are there or not. Remember, a mono AM receiver simply detects the envelope modulation and converts that into electrical signals of audio sound. Thus it always sees the mono side of things.
Same is true in an AM receiver with a C-QUAM decoder. That too simply detects the envelope modulation, but then by aid of the 25 cycle pilot tone, shifts its detector 90* to see the quadrature of the envelope containing the L-R lobes, and decodes and places them inline with the detected L+R and there ya go.
Maybe if you been REAL good this year Santa will drop you a CC system equipped with a C-QUAM exciter!
Well…I still would keep the train set in mind!!
RFB
No Debate
“The bottom line for KDX is that mono = clear talk quality and robust music quality, with the slight disadvantage that the spacial effect is not present for ensemble music. If we were a music station it would be the other way around.”
No debate here. If the format is mostly talk programs, what is the point of transmitting stereo…FM or AM.
My thoughts were this. Since a lot of HD radios, including those in vehicles can decode C-QUAM AM transmissions, why not transmit that C-QUAM and open up the bandwidth gates so that the AM station sounds at its best…plus the added fact my station format consists of 80 percent music related programs, and 20 percent news/talk.
I’ve mentioned it before, I monitor my station’s AM stereo signal 99 percent of the time than the FM stereo signal. To me it has warm smooth stereo sound that doesn’t sound like its about to jump out of the speakers and poke my ear drums out.
Besides..I think AM Stereo got a bad start back in the 80’s and was totally botched up in its introduction and capabilities. Despite that there are a few licensed stations transmitting in C-QUAM, it is still not promoted or demonstrated enough.
So why not at least be different and have something special in the Part 15 world and run the AM in C-QUAM? Someone out there is either listening via a newer HD radio, or a vintage AM Stereo radio (best) and enjoying that slick smooth AM Stereo sound!
RFB
I’m not going to enter into
I’m not going to enter into the stereo vs mono word wars this time – my testing indicated that a clear (and that is the key word) FM mono signal went much farther than a stereo signal. It really depends on the receiver, but I tested on multiple car stereos. As someone wise on this Forum once said, theory is theory, but the real world is everything (I’m paraphrasing).
However, I would also argue that unless your major audience is yourself (or you’re an audiophile), why bother with FM stereo? If you’re listening in the car, there’s so much road noise it really doesn’t matter whether the signal is mono or stereo. Even around the house, unless you’re sitting in between your speakers for an extended period, stereo really doesn’t give you all that much. I’d go for the increased range, clearer signal every time.
Ideas Galore
This website and the discussion forums are so good because they are educational and spark new ideas.
New idea #1 (would not have thought about this if RFB hadn’t mentioned it)- Is it possible to install controls so we can fine-tune the pilot tone and the stereo generator signal? Problem 1 – would void the certification…. but now that you know about this problem don’t you want control?
New Idea # 2 – The best scientific inquiry explores everything, including the impossible, because maybe it can be reversed and made possible….. but here’s a big WHAT IF…..
WHAT IF the present FM stereo method were discontinued and from now on FM radio used C-QUAM as it’s stereo method. One good thing would be the standardization between AM & FM, and I take it that it would NOT have the problems of present day FM stereo. Another good thing is that the upper end of the audio spectrum would be returned to the high-fidelity bandwidth of the station sound….. 19kHz is an AUDIBLE signal and kills the upper-audio-harmonics! FM high-fidelity in mono with all the stereo junk turned off SOUNDS MORE LIVE. The present FM stereo method is imperfect and we should call our Congressman and make this a priority.
???
Can’t for the life of me figure out why the FCC would certify a Part 15 FM transmitter using the BH1415 when most of them do not have that 19Khz pilot level adjusted at all.
Noisy things to say the least.
As to the new idea 2, well phase modulation would work for the C-QUAM approach and still be compatible with current FM detectors, but the stereo part will not be compatible with the FM stereo format.
Im not sure calling congress will do any good..they seem to be fumbling on a bunch of stuff already I doubt putting one more thing on their plates would help balance anything at this point.
End solution…just pull the 38Khz crystal so it kills both the L-R and pilot tone and transmit in glorious mono!
RFB
AWK!!
OK this is a free country and you can just about do anything you want with your sound on FM Pt. 15 as long as it’s legal –FM mono, FM stereo, even AM or CW! But why would you want to vary from what most existing receivers hear as normal? A whole new kind of modulation for FM? Would it even be compatible with the receivers that are out there now? Sounds like another HD radio disaster in the making!
Whatever you decide to do PLEASE, PLEASE DO NOT bypass your transmitter’s filter so you can feed audio of 19khz and above into your FM transmitter! It will drive the stereo receiver on the other end NUTS!! The stereo indicator light will be blinking to the beat of the high end notes, and the receiver will be turning the stereo mode on and off every time it blinks! FM transmitters (the good ones, anyway) have 15khz “brick wall” filters in them. It keeps any audio above 15khz from modulating your transmitter at all! Thank God!
By the way, unless you’re a teenager who hasn’t yet discovered ear buds, you can’t hear at 19khz or above anyway. You lost that ability long ago! Test yourself with an audio oscillator — you’ll see — or get one of those free hearing tests at a hearing aid store. Most of us can’t hear anything over 15khz, which makes that a good place to have a “brick wall filter” start working.
The only other thing I can really add is — My Pt. 15 transmitter is FM stereo, and I LOVE IT! It gets out very well and the stereo sound is FABULOUS! Very, very little difference in the station’s range between mono and stereo. I wouldn’t think of depriving my listeners of stereo unless I was doing an all talk format. Maybe I’m just one of the lucky ones who has a properly adjusted stereo generator, but I LOVE the results! Just my oppinion — Do what ya want!
Do What I Want
I think I will call up my old engineer friend, who back in the 70’s and 80’s was an engineer for one of the old Soviet Union “Electronic Iron Curtain” buzz saw stations. Good fella, very kind and very willing to spill a ton of beans about those systems.
Think I will adapt my FM and turn it into a buzz saw station. Put a 300 hz buzz on the left, and a 600 hz buzz on the right. 😛
RFB
Buzz Saw
I bet you’d have the best sounding buzz saw on the air! Hey! Then you could connect a key and turn your buzz saw into modulated CW! Or even better! — You could put the dots on the left channel and the dashes on the right! Will you send me a QSL card? Never mind…I’d be too dizzy to read it!
rikocher, what is the range
rikocher, what is the range that you’re seeing for FM stereo? And what is it being received on?
Just wondering, because your results differ substantially from mine. I’m in Canada, I get a 1km mono signal with some quieting line of sight, that translates down to about 250 meters or 800 feet for U.S. field strength requirements. That’s using a very sensitive Hyundai OEM stereo (from my Santa Fe – amazing radio for FM reception, the only thing that’s come close in my testing is a high end Alpine). A stereo signal didn’t come close to that range.
And even with obstructions, I can easily get a listenable signal 1/2 km out (although it fades pretty quickly after that).
Range clarification
I have a Toyota with one of the best FM radios in it I’ve heard. 800 – 1000 feet is about right, to where I can’t hear it anymore. I get pretty much the same range whether I broadcast in stereo or mono.
But here’s the clarification: I only get out about 200 – 250 feet before the stereo signal gets noise in it, and the radio will switch itself to mono, for the rest of the run.
My point is this: Since stereo receivers do a pretty good job of automatically switching to mono when the stereo signal begins to get noisy, why should I not broadcast in stereo? I get the same maximum range either way, and the listeners who are close enough to get good stereo can get it. (And some of them really appreciate it. They’ve told me so) Also Don’t forget the BONUS — many scanners will only stop when they detect a STEREO signal! I don’t want a scanner to pass me up.
Oops! Forgot something!
I’m about 30 feet high and all the houses around here are only one story. I shoot over all the houses on the way to the listener’s houses, so in most cases I only have to penetrate the listener’s wall and I’m in!
First I Have Heard
First time ever I have heard of a scanning FM stereo receiver only locking to the stereo pilot. Kind of pointless to rely on the weak 10 percent modulated pilot tone to lock onto a station when there is a much bigger signal to count on to lock on channel. Besides..the pilot tone is not the carrier frequency so why would receiver manufacturers put in extra circuitry to only see a 19Khz pilot tone 19 Khz up from fundamental frequency which is actually the frequency tuned and the fact there are still non-commercial FM’s out there transmitting without a 19Khz pilot tone.
I’m not sure that is correct the radio locks to a stereo pilot tone. If it does..that is one funky and sideways design IMO. Good thing this is the 21st century and not the hey day of early FM, or you would be quite upset at that scanning function in that radio!
RFB
Only Part of the Story
What you have shown, rlkocher, is that your stereo FM radio signal works well with a very good receiver.
To make your conclusions more comprehensive I would suggest running reception tests with several grades of radio, some average, some poor.
I agree, Carl.
Also, I’m not
I agree, Carl.
Also, I’m not sure how the switching to mono works, but I would think that more noise would be introduced into such a mono signal (compared to broadcasting in straight mono).
But hey, if it works for you, that’s great. My experiences differ.
Stereo FM Kit
Back in the 70s a couple engineers I knew started building low power experimental FM transmitters to be able to send stereo music at home.
They gave me a 1-watt mono prototype that was simply 3-transistors with matching coils and tuning slugs for peaking each stage.
I stuck a TV-band VHF antenna in the attic and every Friday night a minister and his wife would tune in about a mile away and I’d play comedy albums and other nonsense and we’d have a radio party.
The stereo version was simple. There was an L+R mix for the mono channel, an L-R mix using either non-inverting/inverting amps or transformer matrix, a tone generator that mixed in with the L+R at 10%, and a sort of transmitter within a transmitter in the 38kHz oscillator that was AM modulated with the L-R signal.
Somebody could easily manufacture such a kit and it would be popular.
I Stand Corrected!
I think it was back in the early ’80s an engineer told me that an FM radio set to scan or seek, only stops at a stereo station. He showed me how his radio did that, and from then on I assumed it to be true. Well just now I put my transmitter in mono and checked my 3 radios that scan. You guessed it! All 3 radios stopped at my station, even tho it was in mono and the stereo lights wouldn’t light. So forget what I reported earlier…RFB is right! (as usual)
I’m standing firm on my other point, tho: Testing on 8 different radios, (some of them are pretty cheap!) I’ve found very little difference in overall range of mono broadcasting vs. stereo. The only difference is, As I walk away from the station as it’s in stereo, the stereo reception will become a bit noisy right before the radios switch over to mono. They all switch back and forth several times as I walk farther away, eventually settling into the mono mode, where they stay until the signal is gone. I don’t find the switching objectionable at all, so I’m staying in stereo.
Sorry I was wrong about the scan/seek function. Didn’t mean to mis-lead anyone.
No Shame No Blame
No worries there friend. After all, someone else simply passed on incorrect information, it happens sometimes.
Your tests seem to confirm the average expected results of the stereo signal’s range and then receivers flipping to mono at that point. All of your tests with the various radios seem to be within reason.
Plus different radios will have slight variances in their front end sensitivity so that plays with plotting range comparisons between different receivers. Their AGC circuits will kick in and ramp up the gain as distance increases, some radios actually injecting more noise than doing their job of pumping up the front end gain.
There really is no reason to butcher up a good transmitter just to make it mono when receivers will take care of the distance/noise issue with a stereo broadcast.
But if mono is the name of the game, there are transmitters out there specifically missing the stereo generator. I would suggest getting one of those and be assured that there is no question it is a pure mono FM signal.
RFB
Advertising Campaign
Idea for promoting a Mono FM station:
“This is X-FM, the GREEN radio station, saving YOU energy by turning off the light on your stereo radio!
“And the good news is, X-FM still comes in ON BOTH SPEAKERS! Just like stereo!”
A green lie?
Back At It
Well, I’ve just had an “out of stereo experience” and decided to revisit the subject of mono and/or stereo.
After reading this whole thread from the beginning back three-years ago, I like it! Everybody described useful experience in their own stereo/mono stations.
In 2012 I converted my shoutcast stream to stereo because I run a certain amount of stereophonic concert programs, and I want to provide the best experience for listeners. This reduced the sampling rate of my stream overall from 44.1kHz down to 22.050kHz, a lowering of quality in exchange for a gain in “spacial” ambience.
But then at the ALPB Meeting last Saturday the subject of mono/stereo streaming came up when I asked a question:
“Computer listeners ALWAYS listen on two loudspeakers, whether a stream is sent in mono or stereo. Can they really tell the difference?”
A discussion followed, in which the consensus of the professional broadcast members was that it was better use of bandwidth to stream in mono and MOST people won’t notice a difference.
Based on that discussion I have officially gone back to the original MONO preference described in my opening post.
Regarding FM stereo, one thing not mentioned anywhere in this thread is that that 19kHz tone, if present when using an FM transmitter to send audio for re-broadcast on an AM transmitter, will cause out of band whistles above and below the main AM carrier frequency.
Back At It
Well, I’ve just had an “out of stereo experience” and decided to revisit the subject of mono and/or stereo.
After reading this whole thread from the beginning back three-years ago, I like it! Everybody described useful experience in their own stereo/mono stations.
In 2012 I converted my shoutcast stream to stereo because I run a certain amount of stereophonic concert programs, and I want to provide the best experience for listeners. This reduced the sampling rate of my stream overall from 44.1kHz down to 22.050kHz, a lowering of quality in exchange for a gain in “spacial” ambience.
But then at the ALPB Meeting last Saturday the subject of mono/stereo streaming came up when I asked a question:
“Computer listeners ALWAYS listen on two loudspeakers, whether a stream is sent in mono or stereo. Can they really tell the difference?”
A discussion followed, in which the consensus of the professional broadcast members was that it was better use of bandwidth to stream in mono and MOST people won’t notice a difference.
Based on that discussion I have officially gone back to the original MONO preference described in my opening post.
Regarding FM stereo, one thing not mentioned anywhere in this thread is that that 19kHz tone, if present when using an FM transmitter to send audio for re-broadcast on an AM transmitter, will cause out of band whistles above and below the main AM carrier frequency.
19 kHz
Regarding FM stereo, one thing not mentioned anywhere in this thread is that that 19kHz tone, if present when using an FM transmitter to send audio for re-broadcast on an AM transmitter, will cause out of band whistles above and below the main AM carrier frequency.
That 19 kHz pilot tone should not be present in the L&R outputs of an analog FM stereo receiver of any reasonable quality.
If an analog stereo FM transmitter running in stereo mode is modulated with monaural audio, then the L&R outputs of a stereo FM receiver both carry that monaural waveform.
Either the L or the R output of that receiver (or their sum) could be used to modulate a monaural AM transmitter without including the 19 kHz pilot tone. The L&R sum would be a little less noisy.
Two Leaky Receivers
I have two stereo radios feeding different AM transmitters, and both receivers pass enough 19kHz to cause out-of-band whistles above and below the main AM carriers.
The Technics ST-9030 has a second output intended for recording, which includes high-end filtering to avoid clash between 19kHz pilot and tape bias, and this works also to solve the AM feed problem.
The other receiver is Panasonic RE-7680, built to a lower “consumer” standard, and its only stereo outputs, marked REC OUT, pass enough pilot to cause out-of-band whistling.
Fortunately the whistling does not show on the spectrum analyzer, unless by a slight activity down in the noise floor, and disappears out in the field, within 100′.
The transmitters that allow killing the pilot have no out-of-banding when fed over AM.
Ears Like A Bat…
Wow, if those radio speakers can reproduce the pilot tone my wife would run screaming from the room. She won’t even set near an old CRT type monitor or TV because of the horizontal flyback noise.
Hetrodining for Lunch
The AM side-band whistles caused by the pilot are not 19kHz, they are more of a mid range howl-whistle, so there must be some kind of arithmetic here.
I’m revising what I said about the whistles fading out within a hundred feet. I went out to double-check, and the whistles, already down in the background noise, remain constant with the main carrier. But they are so mixed into everything they might as well be beat-frequencies from Italy where AMers are being sent to court all the time.