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KRKO/KKXA To Test All Digital AM Broadcasting
- Thread starter Bongwater
- Start date
If you listen to a weaker AM station in an area with a lot of electrical interference, there are always certain spots that are going to give you trouble (I.e., bridges, tunnels, power lines, light rail tracks), I don't see how the digital version of the signal would be any more immune to dropping out.
I'm just saying, it takes a few seconds to regain a digital carrier. Not to mention the analog signal will not be there to fall back on during a "drop" if a station ever elected to go all digital. Its not the same as regaining the signal as soon as the interference is no longer present on the "old fashioned" system.
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Power bills on FM are much higher with HD. The reason is that the peak-to-average ratio is much higher with HD and the transmitter has to be linear to reduce the intermod products. In fact, Gates Air is now offering a retrofit kit for their Z-series transmitters to turn off HD and migrate the PA's to class C.
But that's on FM. Has anyone heard anything at all about how much power (rms or peak) these stations are running in these all-digital AM tests? That seems to be a difficult number to find.
Dave B.
Might that have been an issue with KKXA's transmitter troubles? They'd be running at a fixed maximum output level instead of an AM modulation envelope with a lower power level, I think.
Obviously no one was listening when I said you don't hear the pattern change with AM HD. You have 8 seconds of buffering on AM HD. So you can pass under stuff and not get a drop out. You can turn the transmitter off for 3 seconds and not miss a beat. One thousand, two thousand, three thousand. It's a long time in radio billable time.
I actually got the KKXA day digital here on Vashon but not at my house by the KOMO plant. The Sangean tuner is not the best but I got a lock on KKXA reliably in the middle of the Island. It did sound like double encoded MP3 files were playing. Interesting when they played a Patsie Cline which would have been low-fi in today's recording standards sounded better than the newer stuff playing.
Back to the 8 second delay it took about that long for the Sangean to lack and start to play audio. When switching from a digital IBOC transmitter to the Analog backup it reminds me of switching in and out of the delay used for phone in shows.
The MA3 mode still requires 13KW of carrier on frequency. But the rest is spread across it's, channel, let's just call it. From what I hear the KRKO transmitter was showing 50KW on the output and 31 amps on the common point in MA3 mode. It does appear that the all digital signal on a good HD radio does go farther than the analog.
I actually got the KKXA day digital here on Vashon but not at my house by the KOMO plant. The Sangean tuner is not the best but I got a lock on KKXA reliably in the middle of the Island. It did sound like double encoded MP3 files were playing. Interesting when they played a Patsie Cline which would have been low-fi in today's recording standards sounded better than the newer stuff playing.
Back to the 8 second delay it took about that long for the Sangean to lack and start to play audio. When switching from a digital IBOC transmitter to the Analog backup it reminds me of switching in and out of the delay used for phone in shows.
The MA3 mode still requires 13KW of carrier on frequency. But the rest is spread across it's, channel, let's just call it. From what I hear the KRKO transmitter was showing 50KW on the output and 31 amps on the common point in MA3 mode. It does appear that the all digital signal on a good HD radio does go farther than the analog.
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That is interesting. I would have thought that if you were going into a short tunnel that you would have have reception due to the digital delay, but then you would observe the signal breaking up upon exiting the tunnel because no information was getting to the receiver while you were surrounded by cement. Maybe it doesn't work that way, but that's what i've been told.
I'm not sure there would be any extra effort on the part of a modern AM transmitter to transmit full-digital, at least in theory. With conventional peak-modulated analog-only mode, you set your base or common point current with no modulation, in this case say-31A. Then when modulating the transmitter, your peak power and base/common point current levels of course fluctuate with modulation. With full-digital (RMS) modulation, I'd imagine you set your power output to achieve the licensed base or common point current with digital modulation because there are no peak values. Modern transmitters should be able to maintain 100% modulation at their designed output, whether sine wave analog, or digital modulation. It seems to me the technical wild cards would be external diplexers, phasors, traps, or tuning networks, as to whether they could take the constant RMS modulation for long periods of time and maintain the same bandwidth and equalization important for digital broadcasting.
When TV stations started broadcasting in digital mode, we faced similar challenges. Analog TV transmitters were AM modulated, at least on the visual side. Depending on the picture broadcast, the transmitter would go through peak changes. When digital, the entire 6Mhz of bandwidth is occupied by modulated data and it has to be flat from side to side of that 6Mhz channel. The transmitter had to be designed with the broad bandwidth and power output capability to run 24/7 with constant full modulation. The difference is between FM or TV digital transmission and AM: AM has all those components between the transmitter and antenna.
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I've been told that HD radio is COFDM. So it should be a different modulation scheme than 8VSB television, and should be far more tolerant of group delay problems in the phasors and ATU's. The fact that HD works at all on the back side of directional antenna systems would substantiate this. So I'm not sure we can extrapolate the TV experience to HD radio. There's a pretty accurate yet simple description of the differences here:
http://en.wikipedia.org/wiki/8VSB
Scroll down to "8VSB vs COFDM". It doesn't look like there's really a lot of power savings if, indeed, the common point current remains the same as with analog modulation.
Dave B.
This sounds like "AM Stereo" back in the 1980's. What a concept! Not.
Big differences between AM stereo and HD: AM stereo didn't sound artificial.
It didn't cut out. It could be received 2000 miles away. (An easy listen in California to WLS, and the quality was good.)
AM stereo downside: platform motion during fades.
It's certainly true that the tests showed expanded coverage for the HD signal.
On the other hand, it's a big noise generator, and all-digital wouldn't be compatible with analog on the same frequencies.
It might fly if band allocations could somehow be reallocated by region and by mode, but still I expect that as an all-or-nothing deal, it would be a debacle.
Because unlike a test, there would be many stations to accommodate, and I can't picture a scenario that wouldn't result in an ugly mess.
It didn't cut out. It could be received 2000 miles away. (An easy listen in California to WLS, and the quality was good.)
AM stereo downside: platform motion during fades.
It's certainly true that the tests showed expanded coverage for the HD signal.
On the other hand, it's a big noise generator, and all-digital wouldn't be compatible with analog on the same frequencies.
It might fly if band allocations could somehow be reallocated by region and by mode, but still I expect that as an all-or-nothing deal, it would be a debacle.
Because unlike a test, there would be many stations to accommodate, and I can't picture a scenario that wouldn't result in an ugly mess.
Unfortunately, people who are in favour of I-BLOCK and the use of HD radio will never agree that its a flawed system. I personally think that AM stereo is a great system for audio fidelity, but it too had drawbacks. If there were not as many stations on the AM dial, you would probably have better luck hearing the signals that remained; maybe some of the stations would have the clarity of KIRO 710 (imagine that flamethrower with C-QUAM 
).
When you take everything into consideration, the listening audience had decide that this isn't a system they want to embrace. I don't blame them, I wouldn't want to spend hundreds of dollars on a stereo system to jump on this bandwagon.
).When you take everything into consideration, the listening audience had decide that this isn't a system they want to embrace. I don't blame them, I wouldn't want to spend hundreds of dollars on a stereo system to jump on this bandwagon.
Unfortunately, people who are in favour of I-BLOCK and the use of HD radio will never agree that its a flawed system. I personally think that AM stereo is a great system for audio fidelity, but it too had drawbacks. If there were not as many stations on the AM dial, you would probably have better luck hearing the signals that remained; maybe some of the stations would have the clarity of KIRO 710 (imagine that flamethrower with C-QUAM
When you take everything into consideration, the listening audience had decide that this isn't a system they want to embrace. I don't blame them, I wouldn't want to spend hundreds of dollars on a stereo system to jump on this bandwagon.
AM stereo is still alive and a lot of HD radios will decode it (though they may remain in a narrow IF mode..and it flips left and right channels)...I used to listen to WLS in the top40 80s and it was in Kahn and then CQUAM..this was while driving back roads in SE Texas...and it sounded fantastic!!! The platform motion issue was reduced a LOT in the later chip designs for the receivers....and Motorola still sells the 13028 CQUAM detector chip...some evidently still wants them being made...Nautel AM transmitters can do CQUAM with a simple change of code in its software (Nautel makes it available as an option iirc)..and there still is one company selling NEW CQUAM exciter (1 RU now! compare that to the old Motorola 1300 series with was 6 inches tall!) With DSP power (with a Noise Blanker that works!) and any mandated requirements, AM stereo could see a comeback...I am not holding my breath but I could see it happening if things go right..Also you can retrofit many radios with a aftermarket decoder (if you are savvy enough) OR they will do it for you....
HOWEVER, AM's biggest problem is external...power line, switcher power supplies and other noise sources (hell my car cell charger buzzes all over the band! Time to get a new one
Right now , there are no AMs I want to listen to because they have formats that do not appeal to me...a classic top40 AM?? I would...in a heart beat...(JACK FM on AM??? mmmmmm)I agree with what you say here, ContinuousWave. And what doomed AM stereo was its delay in adoption and the FCC's foot-dragging and dismissing several viable systems. (I think the Kahn system sounded best.)
It was something like 14 years between its installation on XETRA (690 in Tijuana, Kahn-Hazleteen(sp?) system) and the FCC's adoption of CQUAM.
Meanwhile, a good radio had been developed that was compatible with all of them, so the "marketplace" didn't have to decide.
Unfortunately, between 1969 and the certification of Motorola's system, interest in AM formats was waning and music stations were going away as FM gained more market share.,
Unlike IBOC or the very annoying FM system, AM stereo didn't interfere with other signals on the band and it wouldn't render any radios obsolete if adopted by everyone.
Many stations were on board, including WLS, KNBR, KFI, KHJ, KRLA, and KOMO, just to name a few.
What has kept HD alive in the past decade is marketing, something AM stereo lacked. In my view, iBiquity's systems are all steak and no sizzle, and I'm even more convinced of this after the local tests.
Granted, FM "HD" sounds better than IBOC. And if the HD signal didn't interfere with adjacent frequencies, its proliferation wouldn't bother me.
But the AM system really is even more of a bill of goods. It sounds artificial, it creates interference, its wholesale adoption would render most existing receivers obsolete.
Signalwise, KRKO and KKXA's tests were a success, especially KRKO, which has better night coverage in the metro. (In north Seattle, I only get a lock on KKXA on full power, which in the winter would give me five hours a day of HD coverage.)
But a bad system is a bad system. A more resilient method of transmitting a bad system doesn't improve the system itself.
It was something like 14 years between its installation on XETRA (690 in Tijuana, Kahn-Hazleteen(sp?) system) and the FCC's adoption of CQUAM.
Meanwhile, a good radio had been developed that was compatible with all of them, so the "marketplace" didn't have to decide.
Unfortunately, between 1969 and the certification of Motorola's system, interest in AM formats was waning and music stations were going away as FM gained more market share.,
Unlike IBOC or the very annoying FM system, AM stereo didn't interfere with other signals on the band and it wouldn't render any radios obsolete if adopted by everyone.
Many stations were on board, including WLS, KNBR, KFI, KHJ, KRLA, and KOMO, just to name a few.
What has kept HD alive in the past decade is marketing, something AM stereo lacked. In my view, iBiquity's systems are all steak and no sizzle, and I'm even more convinced of this after the local tests.
Granted, FM "HD" sounds better than IBOC. And if the HD signal didn't interfere with adjacent frequencies, its proliferation wouldn't bother me.
But the AM system really is even more of a bill of goods. It sounds artificial, it creates interference, its wholesale adoption would render most existing receivers obsolete.
Signalwise, KRKO and KKXA's tests were a success, especially KRKO, which has better night coverage in the metro. (In north Seattle, I only get a lock on KKXA on full power, which in the winter would give me five hours a day of HD coverage.)
But a bad system is a bad system. A more resilient method of transmitting a bad system doesn't improve the system itself.
If you were talking about my comment, it was a joke.
I think what doomed AM stereo (if you could use the word 'doomed') was that by the time the 'standard' was adopted, most young people had already moved to FM for music programming, and they weren't about to buy a special radio to hear music on the AM band in stereo.
It's all about the timing. The only way you can defeat poor timing is government mandate.
It's all about the timing. The only way you can defeat poor timing is government mandate.
I think it was also A) There were five competing systems of transmission B) Electronics firms and stations decided to sit it out and wait until a standard was established - if ever C) Stations that did broadcast in stereo never promoted what system they were using. And of course, really bad timing....
Otherwise, AM Stereo was an excellent idea. It was just handled in the most incompetent, ham-handed way. The "free market" back then only knew if you turn something on, it should work without fussing around with it to make it work. If FM stereo was handled this way, it would STILL be in mono.
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