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HD Reception in New England

K

K6JHU

Drove round trip the other day from Hartford to Boston. I got a good lock on WTIC-AM HD on the Mass Turnpike. That is close to the limit of AM HD I believe. But as I got outside the range (where is was kicking in and out) the difference in the audio was like night and day. All of a sudden the noise floor would just drop right out when the HD would kick in. Absolute quieting, even under the high tension lines.

On the way back started listening to WCRB (102.5) in HD. Round about Worcester both the HD and the analog started to crap out. So I put on WGBH-HD2 (89.7). Good solid lock all the way to I-84. That is almost as far as the analog signal reaches. Sound quality of the HD2 was better than the Sirius built into the car.

So what I am concluding is that if done properly HD actually provides some very real improvements in sound quality and signal reach depite the fact that there are also some real technical issues to be worked.
 
That's an encouraging post, but I can't help but think that with the crowded FM dial in New England there have to be some stations suffering interference from nearby HD setups, and certain HD-equipped stations not going out well because they're stepping on nearby analog first adjacents.
 
K6JHU said:
Absolute quieting, even under the high tension lines.
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Interesting - because that is the exact opposite of my experience with AM HD. As close as five miles to a local station, power lines cause HD lock to disappear. So does lightning, underpasses, and anything else that causes problem for analog AM. Unfortunately, most streets are lined with power lines. The long lock times meant that HD was out more than it was locked. My conclusion was that HD is a waste of power on AM, because it is so prone to dropping out. I'm glad you are having a better experience with it than I did.

One thing I did notice on a 50 kW station 200 miles away - with HD AM they were very weak in analog, but the moment they dumped HD, the analog signal is crystal clear almost like a local. The audio is crisp and full of highs again, unlike the muffled 5 kHz audio they were putting out. I much prefer the analog signal now, HD when it was available was curiously like a digital stream and very fatiguing to listen to. I don't see how HD, which obviously acts like a power vampire, would help a station penetrate buildings. The power loss is dramatic, and not limited to AM.
 
"The difference between the (analog and digital) audio was like night and day??" Of course it was. Any AM station broadcasting in HD strangles the analog portion to, on average, 5 kHz or less. So naturally anything with response to about 14 kHz, even if the upper two-thirds is fake ("electronically reprocessed to simulate STEREO!!" - 1970s oldies LPs) sounds dramatically better when the digital takes over.

If you actually listen to most AM-HD stations the completely replicated upper register above about 4500 Hz becomes metallic and fatiguing to listen to after a short time. You get an initial "wowee" factor IMHO primarily because of the lower noise floor. But after a while you find yourself reaching for the tuning knob because the digital somehow "doesn't sound right."

Transitions from source to source, in particular, can be jarring with phase errors and additive codec artifacts. Oddly the AM HD codec sounds worst on spoken word programming, the dominant format on AM. I suspect this is because there isn't the complex acoustic matter and harmonics contained in music to mask to artificiality of the codec's sound.
 
On AM I was talking aout the noise floor. Low level power line hash and the usual artiifacts of a weak signal (e.g. fading). When the HD kicked in, that allk disappeared and the audio was absolutley clear. No noise.
 
No question. The silent floor is eerie. But listening to the radio is a composite experience: the question is, is the signal pleasing overall? Of course in extremely noisy environments AM is impossible to listen to comfortably. But when the noise is THAT bad, HD will simply stop working anyway, because the digital is subject to the same disruptions that ruin analog reception.

I would argue that in "reasonable" cases where the signal, be it analog or digital, is not overwhelmed by QRM/QRN, a well-processed analog signal is preferable because it sounds more natural. If we could get rid of the dumb NRSC pre-emphasis and open AMs up to, say, 12 kHz, a clean C-QUAM signal could rival FM without all the digital trickery. There are many extant examples of this from the not-too-distant past.
 
I live in central Ma about 40 miles east of Boston. WBZ was the only AM IBAC station that would even lock at all on my Sony XDR-F1HD tuner at home, the lock would last at best 30 seconds, the noise floor did drop out but the audio was sibilant, screechy and boomy at the same time, VERY artificial sounding. It sounded like an old three way speaker system with a blown midrange speaker. WTIC did not come in at all in HD. There is a 5 KW AM HD station approx 5 miles from here on 580, I have never heard a hint of them in HD. I certainly do hear their white noise all encompassing sidebands though from 560-600 all day sounding like a manic waterfall. I also hear WTIC's, WFAN's, WOR's, WBZ's and many others from at least Chicago and further at night. I travel the Ma Pike many times each week and it is like an RF tunnel, when you pull off the pike the station usually disappears unless it is a local.
When I had my Sony hooked up I would get a lot of HD AM signals (the HD light would flash) at night but NO reception at all not even from WBZ. On the other hand I get plenty of white noise sideband carrier from half way across this country at night. AM HD is an abomination that should be put out of it's misery.
FM HD is also a waste of power and bandwidth although not as bad. Digital radio in another form could perhaps work on a dedicated band but on existing analog bands it is an unwelcome squatter encroaching on other stations signals.
 
Zach said:
That's an encouraging post, but I can't help but think that with the crowded FM dial in New England there have to be some stations suffering interference from nearby HD setups, and certain HD-equipped stations not going out well because they're stepping on nearby analog first adjacents.
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I don't know... I have a big ass Class B 103.7 audaciously running HD in my back yard. There is a 103.3 and a 104.1, also foolishly attempting to run HD, 50+ miles away. They all can be received in full HD. Must be sunspots.

Imposing the death penalty for stepping on first adjacents could possibly reduce those transgressions.

-
 
iyiyi said:
I don't know... I have a big ass Class B 103.7 audaciously running HD in my back yard. There is a 103.3 and a 104.1, also foolishly attempting to run HD, 50+ miles away. They all can be received in full HD. Must be sunspots.
Click to expand...

If you look at the occupied bandwidth you'll see that works fine. Each HD sideband occupies only 1/2 of the adjacent channel (unless there's lots of intermod, but that's another story). So the 103.3 is using 1/2 of 103.5's channel, and the 103.7 is using the other 1/2. The interference problem occurs when the desired station is 1st adjacent to the HD-equipped station.

Dave B.
 
What about pulling the desired station out from between the local and its HD? An example on AM would be tuning to 591 or 592 from my house (almost 8 miles east of 600 KOGO) to get 590 KTIE from San Bernardino, and using a narrow bandwidth setting like 2 or 4 kHz (marked as 1 or 2 khz on my radio cause it's showing audio bandwidth not total RF bandwidth). For FM, my Tecsun isn't quite up to the task to do this, but other than that what about going to, say, 89.65 or so to pull in 89.7 KSGN from Riverside, and duck out from around 89.5 KPBS 4.5 miles south of me and its IBOC? Back to AM, also a couple years ago I was able to pull in 594 JOAK from Tokyo, Japan, using the same principle. (Audio recording of that one is available if desired.)
 
pianoplayer88key said:
What about pulling the desired station out from between the local and its HD? An example on AM would be tuning to 591 or 592 from my house (almost 8 miles east of 600 KOGO) to get 590 KTIE from San Bernardino, and using a narrow bandwidth setting like 2 or 4 kHz (marked as 1 or 2 khz on my radio cause it's showing audio bandwidth not total RF bandwidth). For FM, my Tecsun isn't quite up to the task to do this, but other than that what about going to, say, 89.65 or so to pull in 89.7 KSGN from Riverside, and duck out from around 89.5 KPBS 4.5 miles south of me and its IBOC? Back to AM, also a couple years ago I was able to pull in 594 JOAK from Tokyo, Japan, using the same principle. (Audio recording of that one is available if desired.)
Click to expand...

Analog tuning results with AM HD are very interesting. One time, Dallas local KMKI broadcast dead air in HD, so I did some recordings of the station while I tuned up and down slightly off frequency. What was immediately apparent is that the 5-10 kHz phase modulation only mutes if your tuning is dead center. Even slightly off frequency, the phase modulation degrades into amplitude modulation and sounds like pink noise. It is so sensitive, I doubt that even the digitally tuned radios can get it perfect enough - the circuitry generating the tuning voltage for varactors consists of a digital to analog converter (DAC), and most of them are 10 to 12 bits. That wouldn't be exact enough to eliminate this problem completely, and even if it was varactors are not linear enough to tune exactly center frequency on every AM station across the band. You will hear some degree of noise coming from the 5-10 kHz phase modulated sidebands. And all of that doesn't even take into account the phase response of the AM station's antenna array, which could probably vary several degrees over the HD bandwidth. Bottom line - HD self noise on AM is a huge problem, and phase modulating 5 - 10k assume perfect center tuning.

Let's talk about exact center tuning for a moment. I was able to center the tuning fairly easily, using the HD self inteference "rush" as a guide. When I got the tuning perfectly centered, a secondary effect arose - a weird warbling sound. I can only assume it happens because the sidebands are not perfectly symmetrical - something inherent in the transmission scheme, or perhaps due to the IF response not being perfectly symmetrical.

All of this - except HD rush 1 kHz or more from the center frequency - would be inaudible to a listener when program material is present. But this points again to bad engineering at iBiquity, it shouldn't be the job of listeners to find these problems which should have been discovered in the lab before the system ever went public. A good engineer would not have made the assumptions (1) tuning is perfectly center frequency and (2) IF response is perfectly symmetrical. They should have tested both scenarios and designed a system that works when center frequency is a little off, and IF response is lopsided.
 
JohnnyElectron said:
Is KMKI going to be the 'all digital' AM HD test station in Dallas that they just mentioned today in RW?
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They said medium market, Dallas is a large market at #5. KMKI is a flamethrower, they have listeners up to 300 miles away in Lubbock, substantial enough numbers in Abilene 180 miles away they have done remotes from there. So it is hardly a typical station, it is a super regional signal, maybe one of the largest footprints in the US for a 5 kW station.

If they were going to utilize a flamethrower, I'd suggest one of the Chicago 50kW monsters. I've heard sideband pairs from Chicago, daytime, at a rest stop in New Mexico. Very remote area with low noise - the location and frequencies of the sideband pairs was very obvious where they were coming from. Not a trace of carrier or analog audio, but the pairs persisted. I am convinced if one of them had be pure digital, I could probably have gotten HD lock - which leads to some intriguing DX scenarios! Pure digital might indeed be the answer for AM, or might have been had the system not flopped with consumers.

At night, the situation is even more dramatic. The sideband pairs of WOR are clearly audible in Texas, interfering with things. Throw a null in the direction of NY, the sideband pairs disappear. WOR is never heard in Texas due to regional blowtorches like KGNC and KEEL, but I've often wondered if I could get WOR to lock with enough signal - and override the closer stations.
 
JohnnyElectron said:
Is KMKI going to be the 'all digital' AM HD test station in Dallas that they just mentioned today in RW?
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The station is in a medium market. That probably means market rank 50 to, perhaps, 100. And it's going to have to be a station that is not currently productive, since whatever listenership it has at the moment will disappear. In other words, some broadcaster is going to donate the body of a dead AM to science.
 
rbrucecarter5 said:
They said medium market, Dallas is a large market at #5. KMKI is a flamethrower, they have listeners up to 300 miles away in Lubbock, substantial enough numbers in Abilene 180 miles away they have done remotes from there.
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KMKI does not get "numbers" in Abeline and barely makes the book in Dallas, where it's had a 0.1 share and a cume of around 30,000 total weekly listeners over the last year or so.

And it is hardly a "flamethrower" as it does not even put a 5 mV/m signal over the city of Dallas or over the city of Ft Worth; in noisy metros around 10 mV/m is needed to generate any ratings results...

Remember, this was the old KWFT from Wichita Falls, and it's directional away from Dallas and Ft Worth, even in the daytime.
 
The station is in a medium market. That probably means market rank 50 to, perhaps, 100. And it's going to have to be a station that is not currently productive, since whatever listenership it has at the moment will disappear. In other words, some broadcaster is going to donate the body of a dead AM to science.
Click to expand...

Clear Channel just shut one down in Jackson MS (Deleted) and Cumulus has one silent in New Orleans (KBYU?). New Orleans would be a great testing ground. I think some of the Radio Disney stations are silent also in certain markets.

In other words, some broadcaster is going to donate the body of a dead AM to science.
Click to expand...

I'm sure one can be found somewhere ;D
 
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