Kintronic Talks AM With FCC

xmtrland said:

The NX50 running IBOC HD is also GPS locked. So synchronization of this type of transmitter is already built in.

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ContinuousWave said:

Digital requires timing that analog does not....hence the GPS syncing.

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In the HD Radio system, it's the modulation, not the carrier, that's locked to GPS time. And it's optional -- not required.

A lot of the discussion about time or frequency synchronization of separated broadcasting stations has to do with the synchronization of their carriers, e.g., to remove interference beats that can sound like squealing. That's not what the iBiquity system does. The NRSC-5 standard talks about using the time information to set clocks for user convenience. It could also be used for automatic program guides, like one finds in television, though that isn't implemented.

In HD Radio the GPS sync is optional, and there's a data bit to indicate whether it's in use or not.

jhardis said:

In the HD Radio system, it's the modulation, not the carrier, that's locked to GPS time. And it's optional -- not required.

A lot of the discussion about time or frequency synchronization of separated broadcasting stations has to do with the synchronization of their carriers, e.g., to remove interference beats that can sound like squealing. That's not what the iBiquity system does. The NRSC-5 standard talks about using the time information to set clocks for user convenience. It could also be used for automatic program guides, like one finds in television, though that isn't implemented.

In HD Radio the GPS sync is optional, and there's a data bit to indicate whether it's in use or not.

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I believe ALL radio stations should be required by law to phase lock their carrier frequency to GPS. This would eliminate a lot of problems - and not just with HD radio!

rbrucecarter5 said:

I believe ALL radio stations should be required by law to phase lock their carrier frequency to GPS. This would eliminate a lot of problems - and not just with HD radio!

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What problems would be eliminated? I believe you misunderstood the fact that jhardis was making. The GPS reference for HD radio is optionally used for delay timing related to analog and digital modulation, not carrier frequency reference.

There has been testing and use for mutiple co-channel transmission sites synchronizing carriers (FM booster stations), or calibratng delay to reduce transmitter-induced FM multipath to receivers which effectively beat against each other. But that's about it. Most modern exciters, TV and radio, have such good oscilators, locking carrier frequency to GPS just isn't necessary.

DavidEduardo said:

Plus broadcasters with the most valuable facilities would have seen their investments devalued, while owners of Class A FMs and daytime AMs would have achieved "free" parity with the bigger stations. So the bigger players were dead set against DAB.

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The bigger players may have been dead set against Eureka 147 but it never got that far because the government said no to L-Band and that was that.

One problem it would solve is the beat frequency that happens when you listen to AM at night, and two adjacent stations, one on each side, introduce 10 kHz heterodynes that are slightly different in frequency. They beat together. As annoying as 10 kHz heterodynes are, they are more annoying when they beat. Another problem that would be solved would be platform motion on C-Quam, which I still think is a more robust stereo system for AM than HD.

Not going to happen. Even if you did sync AM transmitters to a common timing source, it doesn't take into account propagation delay between the co-channel stations to the receiver, wherever in the world one was listening from. Some form of the beat would still be there ('And The Beat Goes On'). That, and since stations don't care about out of market listening, there would be zero incentive for AM transmitter manufacturers and stations to lock their carriers to a common source anyway. Fixing things for a dozen DX'ers would be a waste of resources.

I had the opportunity to play with a couple synchronous AM transmitter testing in early 2000's. We synced the oscillators to GPS reference and added appropriate audio delays, but there was still a certian amount of carrier beating caused by propagation delay where the field strength was equal between the sites. Like with FM boosters, which require terrain shielding and location planning using directional antennas to limit a form of generated multipath, AM boosters always have multiple and unpredictable areas of the carriers beating against each other. We also discovered a fair amount of audio cancellation caused by phase nulling in the overlap areas. in the end, the project was shelved because it provided little advantage, verses the hassle.

Kelly A said:

Not going to happen. Even if you did sync AM transmitters to a common timing source, it doesn't take into account propagation delay between the co-channel stations to the receiver, wherever in the world one was listening from. Some form of the beat would still be there ('And The Beat Goes On'). That, and since stations don't care about out of market listening, there would be zero incentive for AM transmitter manufacturers and stations to lock their carriers to a common source anyway. Fixing things for a dozen DX'ers would be a waste of resources.

I had the opportunity to play with a couple synchronous AM transmitter testing in early 2000's. We synced the oscillators to GPS reference and added appropriate audio delays, but there was still a certian amount of carrier beating caused by propagation delay where the field strength was equal between the sites. Like with FM boosters, which require terrain shielding and location planning using directional antennas to limit a form of generated multipath, AM boosters always have multiple and unpredictable areas of the carriers beating against each other. We also discovered a fair amount of audio cancellation caused by phase nulling in the overlap areas. in the end, the project was shelved because it provided little advantage, verses the hassle.

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yep - Mr. Einstein and his time dilation would get in the way, too. Lest anybody think it isn't real - every GPS takes his theory into account or GPS wouldn't work. Synchronizing might have helped a shoestring operation like WAPN, though, and its antique exciter. The oven around the ovenized oscillator had obviously failed many years before. I can't help but think this could be an issue in low budget stations across the country. GPS synchronization would remove the need for ovenized osciallators in exciters. Probably put a lot of stations better on frequency. Although WAPN was just 20 kHz off channel, that was still a LOT. Their exciter had a PLL done with a very old PLL chip - a newer and better IC on a little daughter PC board I made really improved things! A lot of the time the frequency was less than 100 Hz from 91.5 MHz. But when the transmitter shack changed temperatures, it crept up sometimes to a few hundred. Never more than 1000 Hz off. Pretty good for an aging kludge with germanium transistors. But getting back to those ovenized oscillators - best I could do was trim the thing and wait for a replacement, which thankfully was still available. But that was over 20 years ago - I'd be really surprised if the oven part is still working by now. I am concerned about the millions of digital display radios - the tuning steps are bad enough inside of them, AFC non-existent, you really don't want to add a station grossly off frequency to the mix. Especially HD - AM, which quickly coverts phase modulation sidebands from 5 to 10 kHz into amplitude modulated static if the radio is off frequency. Heaven help the hapless AM listener if they have an analog tuned AM radio with a terrible mechanical tuning dial. They never will get on frequency and EVERY AM HD station will sound like a plague of angry locusts.

Kelly A said:

Now back to reality: There are no "wideband" AM tuners available to consumers,

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One - more - time: EVERY as in ALL, EVERY SINGLE AM radio manufactured in the last 30 years (at least) is inherently wideband: http://earmark.net/gesr/Current_Radio_Design.htm Take any radio made in the last 30 years apart and try to prove me wrong. You won't. The ONLY reason why an AM station has limited frequency response today is because they have put a cheap resistor and capacitor in there to make a one pole low pass filter. But limited audio frequency response is not the same thing as wideband radio. Wideband refers to the IF section, frequency response refers to the audio section. If the IF section is limited to 3 kHz like is was more than 30 years ago, it will affect the audio response as well. But NOBODY these days wants to spend all that money on three IF cans, two transistors, and a pile of resistors and capacitors. AM is not worth that money. They will slap a single ceramic filter in there instead and be done with the IF section. MONEY is SAVED. So much for narrowband AM radios. They cost too much so nobody makes them. What's more - if the IF response is 40 kHz wide, you can put some cheap a$$ tuning mechanism like a gear and flexible plastic. Or just put a circular dial on the tuning shaft. Or buy a microcontroller with only a 10 bit DAC generating the tuning voltage in a digital radio. CHEAP, CHEAPER, CHEAPEST! Say it with me for impact: WIDEBAND AM IS CHEAPER! They don't give a cr@p that it would sound better with music. That's just an accident, one they negate by putting a low pass filter on the audio because all people listen to on radio is Rush or football and you don't need good audio for either. Your one half inch tuning knob connected to the tuning shaft of a $5 radio, with a 30 kHz wide IF so you can get the football game tuned without a lot of effort, then low passed so all the crowd yelling doesn't drown out the words "touchdown". That is what AM radio has become. And that will probably never change, unless somebody shrinks the entire AM section into the IC so you don't even have an option of changing the IF bandwidth external components. By the way, I am now seeing AM radios where the ceramic filter is replaced with a capacitor. Yep - no IF bandpass at all. All the selectivity is done by the half inch long ferrite loopstick and the tuning capacitor. That is what was inside of the "football game headphone radio. And if the ceramic filter costs 10 cents and the capacitor costs 0.1 cents - and you make a million of the things and know nobody cares about AM except to hear a sports game, that saves you almost a hundred thousand dollars. Pretty good if nobody notices or even cares if they notice. AM radios are all broadband now. Period. Money talks.

rbrucecarter5 said:

One - more - time: EVERY as in ALL, EVERY SINGLE AM radio manufactured in the last 30 years (at least) is inherently wideband: Take any radio made in the last 30 years apart and try to prove me wrong. You won't. The ONLY reason why an AM station has limited frequency response today is because they have put a cheap resistor and capacitor in there to make a one pole low pass filter. AM radios are all broadband now. Period. Money talks.

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Hate to keep disagreeing with you Bruce, but about six years ago I had a discussion with one of the design engineers from Delphi while at NAB. Specifically, my question was related to the debate as to the quality and limitations of what AM tuners were still left in car radios. My question: Given the NRSC audio bandwidth limits, has Delphi, or other manufacturers to his knowledge, made changes in the design including IF bandwidth in their radios. The answer was not surprising. He told me that most manufacturers, including Delphi many years ago, after standardizing on processor-controlled tuning, were using a one-chip AM decoders which included reduced bandwidth for the purposes of increasing receiver sensitivity. Given the NRSC prescribed limitations of audio bandwidth, there was the opportunity to increase receive sensitivity by tightening the window. Apparently this trend started well over 20 years ago. That being said, he indicated there has been little, or no development in AM receiver technology for many years because lack of demand, combined with the emphasis on other modern media types playing out of the auto entertainment system. Now you have the interest in audio options like Pandora, Slacker, etc., and with GM recently, providing 3G/4G direct connection options in lieu of AM tuners. You can rant about how good AM could sound until the your last breath, but nobody cares anymore.

Kelly A said:

Hate to keep disagreeing with you Bruce, but about six years ago I had a discussion with one of the design engineers from Delphi while at NAB. Specifically, my question was related to the debate as to the quality and limitations of what AM tuners were still left in car radios. My question: Given the NRSC audio bandwidth limits, has Delphi, or other manufacturers to his knowledge, made changes in the design including IF bandwidth in their radios. The answer was not surprising. He told me that most manufacturers, including Delphi many years ago, after standardizing on processor-controlled tuning, were using a one-chip AM decoders which included reduced bandwidth for the purposes of increasing receiver sensitivity. Given the NRSC prescribed limitations of audio bandwidth, there was the opportunity to increase receive sensitivity by tightening the window. Apparently this trend started well over 20 years ago. That being said, he indicated there has been little, or no development in AM receiver technology for many years because lack of demand, combined with the emphasis on other modern media types playing out of the auto entertainment system. Now you have the interest in audio options like Pandora, Slacker, etc., and with GM recently, providing 3G/4G direct connection options in lieu of AM tuners. You can rant about how good AM could sound until the your last breath, but nobody cares anymore.

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I agree that car radios are a different case, because they are all sinking the whole AM section into a DSP chip. The reason for narrowband in car has nothing to do with a desire for narrowband AM - it is narrowband because they have to filter out car interference, interference from all the other cr@p they throw in there like DVD players, Pandora, internet connectivity, the clock in the car's navigation system, high voltage LCD drive for those 9 inch screens, etc. Not to mention the aliasing products from the DSP itself. I know because I interviewed with a car radio designer about 15 years ago - even then AM was problematic because of all the high frequency RF conducting around the PC board. They were dropping the tuned RF stage in their discrete design to lower sensitivity. But - yes - car radios are an exception to the wideband rule. And no - I don't care about wideband AM either, because the only music on the AM dial in my area is foreign, and I don't speak foreign. ANY foreign so I don't hurt a particular nationality's feelings. My comments about wideband AM apply only to home radios, and walkman style radios. But - if it wasn't for DSP algorithms and the interference in a car, the penny pinchers would have mandated the same thing in car radios decades ago.

Even my top of the line Pioneer car radio - with super AM sensitivity - does it all inside a DSP chip, or more specifically, inside the DSP section of an LSI chip. You can't tweak anything without accessing the code. And they default to talk and sports radio bandwidth. it sounds awful and any music you do hear is tainted with DSP sampling errors and sounds awful. I really hope that they never figure out a way of sinking FM into a DSP, because it will sound awful if they do.