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NIGHTTIME HD AIR-POLLUTION in the BOSTON AREA

J

JIBGUY

Last night. late at night, I checked out the lower end of the AM dial, and came to the conclusion that nighttime adjacent-channel hash on AM is definitely a problem, making many 50kw stations' coverage area severely lessened. There weren't too many stations doing it, but ones that were, were WJR-760-Detroit (750 and 770 nearly obliterated), WABC-770-New York (760 and 780 nearly obliterated). When 770 was coming in stronger and somewhat overpowering 760-hash, then 760 was hard to hear, and vice-versa). So as you would imagine, the stronger the nighttime signal, the more severe the associated HD hash on each adjacent channel.

WOR-710 was coming in weak in general, so its hash was not too detectable on 700 and 720.

One station NOT doing HD was WBZ-1030. Actually neither were 1010-WINS nor likely KDKA-1020. Both of those could be heard well.

WXKS-1430-Medford definitely was HD last night. Killed 1420 and 1440, but there's nothing to hear there clearly at night anyway.

Fortunately, very few stations are doing nighttime HD... adding to the list of indications that this ill HD scheme on AM radio will fail.
 
does 880Am signal scream ( a very strong signal in boston? ) I know their signal here in Northern Vt does.
I bet its doing a lot of damage at night
-OZ


JIBGUY said:
Last night. late at night, I checked out the lower end of the AM dial, and came to the conclusion that nighttime adjacent-channel hash on AM is definitely a problem, making many 50kw stations' coverage area severely lessened. There weren't too many stations doing it, but ones that were, were WJR-760-Detroit (750 and 770 nearly obliterated), WABC-770-New York (760 and 780 nearly obliterated). When 770 was coming in stronger and somewhat overpowering 760-hash, then 760 was hard to hear, and vice-versa). So as you would imagine, the stronger the nighttime signal, the more severe the associated HD hash on each adjacent channel.

WOR-710 was coming in weak in general, so its hash was not too detectable on 700 and 720.

One station NOT doing HD was WBZ-1030. Actually neither were 1010-WINS nor likely KDKA-1020. Both of those could be heard well.

WXKS-1430-Medford definitely was HD last night. Killed 1420 and 1440, but there's nothing to hear there clearly at night anyway.

Fortunately, very few stations are doing nighttime HD... adding to the list of indications that this ill HD scheme on AM radio will fail.
Click to expand...
 
It doesn't sound like that here. The so-so signals for 870 and 890 here in New Britain, CT sound the same as usual. Same with 1020 (KDKA-AM Pittsburgh). I get little if anything here on 1040 AM. I have gotten WHO-AM of Des Moines on that spot before, but not tonight.
 
I have a Boston Acoustics Recepter HD... so here's my take on this:

First off, the Recepter is a crappy receiver, not very sensitive at all. That said, after listening since Friday night, I think I can give an objective analysis of this nighttime HD scheme.

With an HD receiver, the digital hash is not very perceivable, even with strong adjacents. What happens, however, is that when an adjacent comes up in strength, those signals on either side drop below the audio threshold of the BA. When the signal strength of both is roughly equal, both signals are listenable. In the case of two adjacent HD signals, what happens is that the HD will flash once the digital signal can be detected. When this happens, generally speaking, the tiny transmitted signals are enhanced, even if you don't get an HD lock. Thus, interference, again, is not a huge factor when using an HD receiver.

I am NOT impressed with the BA. I could only decode ONE station, WPHT Philadelphia, even though I got the HD indicator to flash on about a dozen signals. And, the one time it decoded, as soon as the signal wavered, the lock dropped. So I got about 5 seconds of true HD audio.

Now, compare that with when I went to the car radio and drove around. The digital interference from strong HD stations was almost unbearable. I have to totally agree with Jibguy. WJR almost completely wiped out WABC and WSB with digital white noise, but this while on the BA receiver in the house I could still receive both quite well.

Analysis... The audio quality of some AM HD streams is simply amazing when properly decoded (others sound too narrowband and grainy, possibly explained by a too slow streaming bit rate?). AM HD in general, including nighttime use, could become a very good and useful thing if two things were to happen. First, there must be a serious upgrade in receiver technology. Sensitivity is horrible, but if it were to be improved upon, signal strength would be greatly enhanced. Second, I believe that the current AM HD scheme could be altered to transmit a slightly more narrowband signal (and corresponding receiver technology could upgrade to more sensitive and more narrowband filters), and still decode a quality signal.

This technology is still in its relative infancy, with this time period now being the big test. My feelings on HD are now one of embracing and refining. We can not go back to analog only. AM radio is not listened to except for persons looking for news or sports features, the latter now really beginning to move to FM. If this band is going to have any use in the future, then a higher-fidelity AM band is going to have to emerge. That's reality. Trust me, I miss WABC and WLS too, but they aren't the stations we grew up with.

Gang, this is not 1965 and we don't all have wideband AM receivers in our cars. You wouldn't want them now anyway due to all the computer and electronic noise, speaking of which the noise floor on AM has risen to a point that one has to go way out into unpopulated areas just to hear decent AM signals. This has to be refined and a method of decent decoding and interference reduction defined, because I'm convinced that the HD technology works, it just needs improvement.
 
Yeah, the Boston Acoustics Receptor-HD has been much-maligned in many engineering circles for poor AM sensitivity. Pity, it's got nice design and good sound. :-\

I have a Directed Electronics DMHD-1000 tabletop HD receiver and it's AM reception is pretty good (the FM reception is amazingly good) and I'll see tonight if I can DX some HD signals. :) FWIW, I don't have an HD receiver in my car...yet...but last night I was driving westward on the NY Thruway...listening to WBZ, WFAN, WTIC and KDKA on my analog car radio until midnight, and I did NOT hear the telltale "white noise roar" on any on the adjacent channels. (shrugs)

Also FWIW, while still in MA, I did notice that WCRN was rather fuzzy...but in retrospect I was probably too far west to reliable hear them anyways; I was just trying to catch the game whilst heading west on I-90 so I switched to WVEI-FM instead. Speaking of which, after I left WVEI's range, but before I could get WTIC's skywave cleanly, the only alternative I found on the fly was WTMM 104.5 in Mechanicsville (north of Albany) Although it was painful to listen to those Yankee announcers ;D I was really impressed with the signal. I could listen fairly cleanly from Lee, MA all the way out to Utica, NY. Not bad for a Class A.
 
I have a hunch that there's really just a couple of main offenders in the white noise category. WJR and WOR. It was nowhere near as bad trying to DX anywhere else on the band. WJR is so widebanded as to cause interference several KC either side of their assigned frequency. WOR has been a notorious offender from day one of HD operation.
 
WJR is broadcasting in STEREO HD, so my guess it that it requires even MORE bandwidth.

The amazing thing is, on my Directed Electronics radio, is that it has a way to significantly reduce HD noise in analog mode from 2nd adjacents when it sounds like hell on the Chrysler analog radio. I also had 3 areas on the radio where the mixing and hetrodyning are horrible with 3 clears all having an HD battle.
 
JohnnyElectron said:
WJR is broadcasting in STEREO HD, so my guess it that it requires even MORE bandwidth.
Click to expand...

All of the Boston AM HD stations are in stereo HD. I hear full stereo on WBZ, WMKI and WXKS-AM on HD.

WBZ was in HD overnight last night (Sunday night/Monday morning). WMKI and WXKS-AM were too.

The only other one around here yet so far is WNNW. I'm not close enough to get their HD.
 
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