Is it my radio?

[rbrucecarter5]

Finally, Yes, I do not believe that you know the difference between the Motorola/Kahn settings on your SRF A-1.
If you understood the difference between quadrature and ISB, the SRF A-1 -- and your ears -- would have clearly explained it to you. But, since we are having this conversation...

The switch was absolutely in the C-Quam / Motorola position.

I used to listen to WLS at night, too. On a Toyota AM stereo car radio in Houston. Never a problem at all with dropouts into mono, although the two channels would swap - rather annoyingly.

AM HD is poor in Houston, 1590 drops out of HD lock repeated as little as 5 miles from the station. All the regular places I would expect AM problems, like near power lines, cause it to drop out of lock. I don't think there is any other station left in Houston doing AM HD.

On the FM side, I find HD-2 dropouts to mono to be extremely annoying. Audio to blank, audio to blank. Much more distracting to a driver than picket fencing or static fades. This on full class C station only 40 to 50 miles away. Pathetic performance. All the usual places you would expect problems with FM - low spots, near large concrete structures, etc. Full class C analog around here goes 100 miles with no problem at all. HD - not so good. If you are stationary and have an antenna, maybe. In a car, well, scale it back to the geometries and power levels / tower heights in major East coast cities - especially in mountainous areas - I doubt they would go more than 15 to 20 miles in HD.

 

[rbrucecarter5]

There is the problem. Or "the problems".

First, any test on an AM should be vs. the usable market area analog signal. That is, "how do they compare in the area where the station gets 90% or so of its measured listening." You were about 200 or so miles too far away for a test of the way the real world uses radio.

Then you picked two stations that are not likely to be the best financed, best equipped and best maintained in the market.

In my experience, the in-car HD signal is better than the analog signal for both KFI and KNX in the LA and surrounding areas. I can get full HD with no noise and better quality than the analog, which has noise, mostly man made, in the outer reaches of the extended LA market (northern San Diego County, Riverside/San Berdoo metro, Ventura COunty) and it actually makes noisy analog AMs listenable when one switches to HD.

Unfortunately, there are only a few hundred AMs in the US good enough to have a decent metro signal in the top 200 or so metros, and putting HD on any other station is a waste.

OK, once again, I'll repeat myself. I needed to get enough decrease in signal strength to hear platform motion. Both stations are regional blowtorches, especially out west. Not what you would expect from poorly financed operations. In fact, KMKI was the flagship station of their network until 2008 or so - and very well funded and maintained. I also needed mountainous terrain - hard to come by in flat Texas, in order to confirm or debunk claims of platform motion caused by mountains in Los Angeles on C-Quam stations. I think I did enough diligence to debunk it.

Also - related to distance - nobody expects those two stations to program to rattlesnakes 290 miles distant. But the SRF-A1 is an outstanding portable, much better than most radios. Scale back the radio quality, put it inside an office building in downtown Dallas, etc. - and we are probably talking about significant coverage issues on normal radios used the way most people use them. Office workers are streaming, making HD AM a moot point, probably FM HD as well. I did have access to a $30,000 Agilent spectrum analyzer. I put it on an extension cord, put it on a local signal, with its recommended antenna. RF power halves every 9 feet in a typical re-enforced steel structure. This means doubling the station's power is equivalent to one row of cubicles. On FM - on AM the spectrum analyzer had to be within 10 feet of the window to see carriers from local 50 kW blowtorches. Any further in, they were obliterated by interference. Because the aisle surrounding the cubicles was by the window and 8 feet wide, that doesn't leave much potential for AM HD in buildings.

I've posted the dismal AM HD results in another post. Robust? Hardly. If you are lucky enough to get AM HD from KFI and KNX 100 miles out, it is probably the difference between 50 kW stations and the highly direction 5kW high band station I was testing. No doubt I would get similar results. But I'd also venture to guess - anywhere near power lines or other interference sources and your 100 mile AM HD would drop like a lead weight.

 

[Savage]

As someone who was building a new AM station while working as a jock at WKBW (actually, then WWKB) 1520 in its C-Quam AM Stereo days, let me weigh in here. KB is a special case.

KB's array was built prior to the NARBA shift in 1941, so its 3-tower inline array is actually a correct halfwave at the station's original frequency of 1380. The towers were never shortened for 1520 operation nor, of course, was the system ever designed to prospectively accomodate a future innovation like AM Stereo. KB is uniquely plagued by skywave-groundwave cancellation and self-interference. Longtime listeners are well aware of the weird shortwave-style "phasing" characteristic of the station's nighttime signal outside of the dominant groundwave.

Of course this unique didn't play well with C-Quam. My car stereo at the time (1986) had six-speaker surround, and I would have to push the MONO button after a while, because not only would the platform image shift from side-to-side, it would start circling the interior of the car, first slowly, then faster - balance, and then slowly start to reverse. It was actually nausea-inducing.

During the daytime and well within the groundwave contour, 1520 sounded terrific, mono and stereo. KB is a unique case and in no way representative of typical C-Quam performance.

 

[davideduardo]

I also needed mountainous terrain - hard to come by in flat Texas, in order to confirm or debunk claims of platform motion caused by mountains in Los Angeles on C-Quam stations. I think I did enough diligence to debunk it.

We turned off C Quam at 50 kw KTNQ in LA in about 1996 because the platform motion was nauseating. On a drive with the DoE of the station, we had to pull over so he could get out of the car and heave...

And the C Quam caused enough artifacts in the sharper null areas of the DA that, when we turned it off, the ratings increased by about 800% in the metro ZIP codes that were affected (a small impact, overall, but ample proof that we had a problem with C Quam).

Scale back the radio quality, put it inside an office building in downtown Dallas, etc. - and we are probably talking about significant coverage issues on normal radios used the way most people use them. Office workers are streaming, making HD AM a moot point, probably FM HD as well.

Many larger companies clamp off streaming in offices. In any case, "at work" listening is a whole lot more than streaming.

If you are lucky enough to get AM HD from KFI and KNX 100 miles out, it is probably the difference between 50 kW stations and the highly direction 5kW high band station I was testing.

I get an in-car HD lock on KFI and KNX at a point midway between the 5 mV/m and the 2 mV/m countours of each. KNX, at 1070, is signifcantly inward of the 640 KFI lockable contour.

That point is well beyond the roughly 10 mV/m usable contour for analog; LA is very noisy and the fact that dust "bakes" onto every power line insulator making it even worse in the 9 dry months is no help.

Anecdotally, I have had KFI consistently lock on HD from Chiriaco Summit to outside of Blythe on the I-10 Freeway... roughly 150 to 250 miles from the KFI site.

But I'd also venture to guess - anywhere near power lines or other interference sources and your 100 mile AM HD would drop like a lead weight.

Nope. There are a couple of multi-level freeway over/underpasses in the metro where HD unlocks, but elsewhere there is no problem.

 

[satech]

Of course, KFI is as good as it gets on AM: 50,000 watts non-directional, on the lowest clear channel frequency. They once called themselves "Western America's most powerful radio station". So IBOC ought to work well on KFI regardless of all its shortcomings.

On the other hand, when you have a tight directional array, in an area of relatively poor ground conductivity, higher up on the band, with adjacent channel stations in neighboring cities, you end up with this:
http://www.youtube.com/watch?v=UtPIK3JM4C8

 

[Savage]

I've been in Philly and witnessed KYW doing that in Conshohocken. I think it's about six air miles from their site. And there's nothing you can do about it, since you can't defeat HD on many radios. (Other than just turn the radio off, that is.)

 

[davideduardo]

Of course, KFI is as good as it gets on AM: 50,000 watts non-directional, on the lowest clear channel frequency.

KNBR, for all practical purposes, is just as good a facility. 50 kw non-DA on 680.

On the other hand, when you have a tight directional array, in an area of relatively poor ground conductivity, higher up on the band, with adjacent channel stations in neighboring cities...

In the top 100 markets, there are fewer than 175 stations that cover at least 80% of the market population day and night. Some of those are very tight directionals that shoot power over a city, generally out to sea...

That means that there are very very few stations that might benefit from HD on AM, even if receivers were more prevalent. The others should stay away from it... 1590 in Houston being an example of a station that should not use HD.

BTW, the ground conductivity in the LA area is good (but not Great Plains "great") around the coast, but as you move inland it gets rapidly poor. The Palm Springs area has as bad conductivity as you can find, for example.

 

[tomservo]

Of course, KFI is as good as it gets on AM: 50,000 watts non-directional, on the lowest clear channel frequency. They once called themselves "Western America's most powerful radio station". So IBOC ought to work well on KFI regardless of all its shortcomings.

On the other hand, when you have a tight directional array, in an area of relatively poor ground conductivity, higher up on the band, with adjacent channel stations in neighboring cities, you end up with this:
http://www.youtube.com/watch?v=UtPIK3JM4C8

Actually that was better than I would have expected for being 60 miles out from Philly.

 

[ajc_trw]

On the other hand, when you have a tight directional array, in an area of relatively poor ground conductivity, higher up on the band, with adjacent channel stations in neighboring cities, you end up with this:
http://www.youtube.com/watch?v=UtPIK3JM4C8

Is it just KYW or do all AM-HD speech stations have that buzzing kazoo sound to them. IMHO it's distortion to the point of distraction so much so that fading back to sub-AM quality was sweet relief.

And I stand by my YouTube comment, it's worth paying for data to hear it properly on an iPhone app.

 

[iyiyi]

As someone who was building a new AM station while working as a jock at WKBW (actually, then WWKB) 1520 in its C-Quam AM Stereo days, let me weigh in here. KB is a special case.

KB's array was built prior to the NARBA shift in 1941, so its 3-tower inline array is actually a correct halfwave at the station's original frequency of 1380. The towers were never shortened for 1520 operation nor, of course, was the system ever designed to prospectively accomodate a future innovation like AM Stereo. KB is uniquely plagued by skywave-groundwave cancellation and self-interference. Longtime listeners are well aware of the weird shortwave-style "phasing" characteristic of the station's nighttime signal outside of the dominant groundwave.

Of course this unique didn't play well with C-Quam. My car stereo at the time (1986) had six-speaker surround, and I would have to push the MONO button after a while, because not only would the platform image shift from side-to-side, it would start circling the interior of the car, first slowly, then faster - balance, and then slowly start to reverse. It was actually nausea-inducing.

During the daytime and well within the groundwave contour, 1520 sounded terrific, mono and stereo. KB is a unique case and in no way representative of typical C-Quam performance.

I agree. I was pretty sure that KB had 225 degree radiators (5/8 wavelength). A 5/8 wave antenna emits an extra, high angle lobe that bounces off of the ionosphere and returns as an interfering skywave. This begins to clobber the groundwave about 35 miles from the xmtr.

Example: WSM in Nashville had to physically shorten it's antenna by many feet because the self interference severely damaged reception in Chattanooga, 120 miles away.

I checked FCC AM Query. Uncle Charlie states that KB has three, 194.7 degree radiators, which is consistent with the "ballpark" 1/2 wave tower electrical heights of most Class A stations. I wonder if detuning skirts were added to shorten the electrical heights of KB's radiators to eliminate their self-interfering, sky wave signals?

I remember the KB signal exactly as you have described it.

-

 

[rbrucecarter5]

We turned off C Quam at 50 kw KTNQ in LA in about 1996 because the platform motion was nauseating. On a drive with the DoE of the station, we had to pull over so he could get out of the car and heave...

And the C Quam caused enough artifacts in the sharper null areas of the DA that, when we turned it off, the ratings increased by about 800% in the metro ZIP codes that were affected (a small impact, overall, but ample proof that we had a problem with C Quam).

Many larger companies clamp off streaming in offices. In any case, "at work" listening is a whole lot more than streaming.

I get an in-car HD lock on KFI and KNX at a point midway between the 5 mV/m and the 2 mV/m countours of each. KNX, at 1070, is signifcantly inward of the 640 KFI lockable contour.

That point is well beyond the roughly 10 mV/m usable contour for analog; LA is very noisy and the fact that dust "bakes" onto every power line insulator making it even worse in the 9 dry months is no help.

Anecdotally, I have had KFI consistently lock on HD from Chiriaco Summit to outside of Blythe on the I-10 Freeway... roughly 150 to 250 miles from the KFI site.


Nope. There are a couple of multi-level freeway over/underpasses in the metro where HD unlocks, but elsewhere there is no problem.

I guess it was you who posted about platform motion. Your experience is vastly different from mine. The swapping channels at night is as bad as it ever gets for me. And rugged terrain - I tried and tried - I hiked all over that canyon. Up one wall, up the other, looking for parallel cliff faces, perpendicular cliff faces - no platform motion. None at all. Only good stereo separation, slight background static. 290 miles - I was impressed! What a robust and reliable system it was. If there had been the slightest tendency for platform motion, it would have shown up, I know what you are talking about - what to listen for. it just wasn't there. It is possible a 5 to 7 mile wide canyon is smaller than the 30 to 40 mile canyons in LA. But both are significantly larger than the wavelength of the station, so I wouldn't think so.

But your observations are obviously valid, you observed them. I observed my observations. There is some unknown variable at work here. I do know both KMKI and KAAM are very well funded operations by people that really care about their audience, and the robustness of the signal bore that out. Obviously so are the large LA stations, so I doubt it is any lapse on the engineering staff at any of the stations. Unknown factor - that's the only explanation why you got platform motion and I didn't.

I've now had the opportunity to do drive tests on AM HD. I can tell you honestly - the biggest enemy it has is the power grid. Unfortunately, power lines run along streets and that is the end of HD lock as long as you are by power lines. As little as 5 miles from the station, and it is 5 kW. Your 150 to 250 mile reception is puzzling, WOAI is 180 miles away, they are a blowtorch, analog is strong and clear, people report it in HD from SA and Austin. Nothing here. Not even away from power lines, away from structures, in the clear, nothing around to cause a problem - nothing. No HD lock. Back to local HD. Lock time is another problem. In a thunderstorm - lightning bolt, HD lock gone for at least 5 seconds. Under an overpass, HD lock gone for at least five seconds. Power line over the freeway, HD lock gone for 5 or ten seconds. My worst fear - dropping out of lock to hear a very loud power line buzz abruptly - happened multiple times. Side street with power lines, HD is gone. This is going on near enough to the station it shouldn't be happening. Head unit is Pioneer's top of the line 9400, and I've still got the 31 inch whip. Pioneer makes a good RF chain- clear on WOAI, clear on WBAP - AM is hotter than Pioneer has made in many years. Oh - and if platform motion made your colleague sick - some of the almost drops on AM HD would, too. Bizarre echos, chirps, whizzes, and in one case a very loud artifact, probably 20 dB louder than either the analog or the HD - one syllable in the voice, one note in the music - very loud and startling, several times. This would be a safety issue when driving for the easily startled.

FM - 103.5 from Austin almost strong as a local. Nothing wrong with the RF performance on FM. FM has a huge problem with nearby lightning, too - HD lock ends, those highly touted HD-2 channels abruptly go silent with every nearby strike, taking 5 to 10 seconds to come back. Extremely annoying.

We are radio people. We know the technology and trade offs. Based on what I heard, I wasted my money on a car radio. HD-2 is not reliable enough to be enjoyable. I am only 30 miles from a full Class C 2000 foot tower 100kW, flat terrain. Intermittent drop outs. NO consumer will ever want to put up with this stuff. It is way too unreliable. Your experience may be different, and that's OK. But my experience is what it is, too. As way too many people point out - DX'ers like myself are outmoded neanderthal throwbacks to a bygone era of radio or something. But without DX techniques, I'd have returned every HD radio I own as defective because there wouldn't be a chance of HD lock without decent antennas.

Mark me down as "not impressed". Three HD radios in - and several hundred dollars poorer - I am left with two home tuners that need a deep fringe yagi to get local stations in HD lock (we are talking GOOD HD tuners from Sangean and Sony- not junk) and a Pioneer Supertuner 3D that DX's AM and FM all day, but AM buzzes with power line noise for miles and miles even really near the station, then locks in HD for a few seconds when I drive a patch of road without power lines beside. It is a really bad joke and not even close to robust or reliable. The new Pioneer was because the old one was failing after several years of use. It just happened to have HD. I am not impressed with HD. Perhaps I will try the bottom loaded large whip approach and see if a DX antenna on a car will give better HD lock.

 

[davideduardo]

I guess it was you who posted about platform motion. Your experience is vastly different from mine.

Two things were different: first, a fix was done to correct the major platform motion artifacts... but by the time they did that, AM radio for music was very, very dead. Second, I make my observations on signal in the areas where people will actually listen and where that listening counts, which means inside the "home" MSA. Listeners outside a metro are seldom if ever of any value sales-wise.

There is some unknown variable at work here. I do know both KMKI and KAAM are very well funded operations by people that really care about their audience, and the robustness of the signal bore that out.

KAAM was a less than optimal operation until Crawford bought it a few years back.... it had more construction modifications than I am used to ever seeing. Hopefully they fixed a lot of the issues, as they are a very engineering focused company, despite the bad night facility. The Disney operations seem to be in a state of general neglect... they actually turned off a number of them last year and those that did not sell were given back to the FCC. Totally inadequate factilities like the one in Houston will likely be killed in the future, based on past performance, will be eliminated by sale or closure.

As little as 5 miles from the station, and it is 5 kW.

A 5 kw station on 1590 is hardly a poster child for anything, unless it is for the reasons AM is dying. The Analog signal is not very usable in a noisy metro, either.

 

[satech]

Crawford had some really top-notch C-Quam station, KAAM being one of them, until they jumped on the IBOC bandwagon and also followed Clear Channel's directive of using 5 kHz audio bandwidth even on stations not transmitting IBOC. But now that they've wisely dumped IBOC, KAAM should switch the AM Stereo back on, given that the facility has already been optimized for C-Quam.

Crawford even had their own solution for eliminating "platform motion", which worked on all AM Stereo receivers, even those using the original MC13020 decoder chip. It involved offsetting the station's carrier frequency (but still within the FCC tolerance), which would turn the platform motion created by co-channel interference into a much less annoying fast fluttering effect -- too fast for the ear to perceive any side-to-side shifting. With this fix, Crawford reported significant improvement in nighttime C-Quam reception in the station's local and fringe groundwave coverage area.

 

[Savage]

I've been out to Big Tree Road in Hamburg numerous times since the days I last worked there, 1986, and I can testify there were never any modifications to the array that I could see. As you know the 1520 array has a common tower with co-located WGR 550 which until Entercom's acquisition of both stations post-deregulation, was owned by someone else. Any re-tuning tricks would have to include both stations, an unlikely proposition then as now (but for different reasons.)

I also worked at KB as a weekend jock in 1969-70. Back then the main Tx was a plate-modulated and huge Westinghouse HG-50 with open-wire 230-ohm feed system to the towers. The array was modernized in the 1970s with 50-ohm Heliax and new LTUs and of course today there are PWM 50kw transmitters on site (the Westinghouse and a Continental 317-C2 are long gone) but the towers look very much original.

 

[rbrucecarter5]

I guess it was you who posted about platform motion. Your experience is vastly different from mine.

Two things were different: first, a fix was done to correct the major platform motion artifacts... but by the time they did that, AM radio for music was very, very dead. Second, I make my observations on signal in the areas where people will actually listen and where that listening counts, which means inside the "home" MSA. Listeners outside a metro are seldom if ever of any value sales-wise.

There is some unknown variable at work here. I do know both KMKI and KAAM are very well funded operations by people that really care about their audience, and the robustness of the signal bore that out.

KAAM was a less than optimal operation until Crawford bought it a few years back.... it had more construction modifications than I am used to ever seeing. Hopefully they fixed a lot of the issues, as they are a very engineering focused company, despite the bad night facility. The Disney operations seem to be in a state of general neglect... they actually turned off a number of them last year and those that did not sell were given back to the FCC. Totally inadequate factilities like the one in Houston will likely be killed in the future, based on past performance, will be eliminated by sale or closure.

As little as 5 miles from the station, and it is 5 kW.

A 5 kw station on 1590 is hardly a poster child for anything, unless it is for the reasons AM is dying. The Analog signal is not very usable in a noisy metro, either.

Well, as I stated before, I had to get far enough away that the RF was down a bit, and to find mountainous terrain. 290 miles on those blowtorches may have equated to 100 miles out West, depending on ground conductivity. But it does highlight what may have been the mysterious variable - too much RF. If you have 50 kW stations pumping out power, they could be creating their own co-channel interference, leading to platform motion. But you would have a fixed, phase locked frequency offset, which wouldn't be conducive to "beating" and therefore platform motion. And it would explain why Crosbyton Canyon didn't have the effect - the RF was still strong enough for clear reception, but not for reflections. But it is still puzzling why KKOB didn't cause platform motion on KAAM - because it was probably well above the 20 dB threshold under KAAM. Had I known this, I probably could have tested in the Red River valley much closer to both to see if I got reflections and platform motion there.

I was in no way implying that any station would care about listeners that far away, but perhaps WBAP does because they have a history with long haul truckers listening. They shut HD down so they could get their coverage back. And KMKI has a small, but loyal contingent of Lubbock listeners. They had so many Abilene listeners 200 miles distant that they did at least one remote out there, maybe two. No days, their business model seems to be shifting to online listening, but do not underestimate their influence. Several Disney artists have succeeded, they are on Radio Disney, introduced by Disney on TV shows, etc. Next thing you know, they have songs on top-40 and are being interviewed by Ryan Seacrest on KIIS. And they continue to have new songs - careers started on Radio Disney. So - somebody is definitely listening, whether over the air or online.

The 1590 folks have contacted me directly a couple of times. The problems came from the KYOK days - the facilities and transmitter sites were a wreck. They put in big dollars to correct the problems, the antenna site had all ground radials ripped out (of course). They have fixed as many problems as they can, and are getting about all they can out of the license. They care, they are hard working engineers like us. But the lack of HD coverage is still shocking. Motivate, competent engineers who really care, and 5 miles from the tower arrat a power line can knock out HD. The problem isn't KMIC - it is HD. When they dropped HD for a few weeks, the analog coverage was way better, it punched through even at night, when the pattern is severely over the Gulf. Once HD returned - no night reception at all in my location. I wouldn't say a 3 dB power loss. Probably closer to 10 dB - as close as I can estimate without a calibrated spectrum analyzer.

Of course KMKI really cares about their pattern. They have to stretch close to 100 miles to cover all the western suburbs of Ft. Worth, which probably accounts for their Abilene, Lubbock audience. Amazing engineering, their notch to protect Milwaukee at night is probably 30 feet wide a few miles from the towers. Really good mechanical alignment! My daughter's babysitter happened to live in that notch, you could literally walk a house or two down the street either direction and get KMKI, but in her house - it was all Milwaukee on 620.

When you have engineers that sharp at Disney and Crawford, it isn't some budget rinky dink amateur hour, my hats are off to them - job well done. They got the best they could out of C-Quam, and they are getting the best they can from HD. Its just HD isn't up to the challenge.

 

[iyiyi]

There is not a doubt in my mind that co-channel AM's would all do best if they were all synched to NIST's WWVB.

It's even easier than that. Take three co-channel stations with mutual interference. Lock one to WWVB, another one to GPS, and the third one synched to a PBS TV color burst signal. No more mutual carrier beat problems! There is no excuse for a modern transmitter to be anything other than dead-on accurate frequency.

-

 

[rbrucecarter5]

There is not a doubt in my mind that co-channel AM's would all do best if they were all synched to NIST's WWVB.

It's even easier than that. Take three co-channel stations with mutual interference. Lock one to WWVB, another one to GPS, and the third one synched to a PBS TV color burst signal. No more mutual carrier beat problems! There is no excuse for a modern transmitter to be anything other than dead-on accurate frequency.

-

There is plenty of problems with that approach. The delay inherent in a feedback system - which by definition is not zero - will result in slight flutter in the carriers, which will beat together worse than they do now. Probably not noticable for analog signals, but I bet it would destroy HD lock, which seems to be tenuous at best. I'm back to satellite radio, having largely given up on HD radio as too flakey, even over flat terrain, full class C stations, towers visible 20 miles away - and HD dropping out of lock.

 

[satech]

All AM HD stations are required by iBiquity to lock their carrier to WWV or some other stable reference. In fact I remember iBiquity claiming that if all AM stations transmitted HD, co-channel carrier beats would be eliminated because of this. However, in that fantasy land, there would be so much "hash" covering up the band that you wouldn't be able to tell if the carriers were in synch or not!

 

[iyiyi]

There is not a doubt in my mind that co-channel AM's would all do best if they were all synched to NIST's WWVB.

It's even easier than that. Take three co-channel stations with mutual interference. Lock one to WWVB, another one to GPS, and the third one synched to a PBS TV color burst signal. No more mutual carrier beat problems! There is no excuse for a modern transmitter to be anything other than dead-on accurate frequency.

-

There is plenty of problems with that approach. The delay inherent in a feedback system - which by definition is not zero - will result in slight flutter in the carriers, which will beat together worse than they do now. Probably not noticable for analog signals, but I bet it would destroy HD lock, which seems to be tenuous at best. I'm back to satellite radio, having largely given up on HD radio as too flakey, even over flat terrain, full class C stations, towers visible 20 miles away - and HD dropping out of lock.

Nope. All each station needs to do is lock with any known good frequency standard. No synch is required between stations. Sure, skywave and other factors can cause signal degradation, and co-channel modulation may cause some interference. Hands down, co-channel carrier heterodyne beats far exceed the problems caused by all of the other interferences combined.

A good example is your KAAM/KKOB observation. You have heard it in action!

-

 

[rbrucecarter5]

Nope. All each station needs to do is lock with any known good frequency standard. No synch is required between stations. Sure, skywave and other factors can cause signal degradation, and co-channel modulation may cause some interference. Hands down, co-channel carrier heterodyne beats far exceed the problems caused by all of the other interferences combined.

A good example is your KAAM/KKOB observation. You have heard it in action!

-

Of course, the beat frequency was so low that it would have been inaudible. It did cause reversal of the two channels on C-Quam, but it was close enough in frequency it would have been about 1/5 Hz at most. Pretty good accuracy out of 770,000!