The Day the AM Band Died

[R.F. Burns]

For the love of God, someone explain to this person what a "beat" is. You keep comparing it to audio. It's an RF beat, causing their modulated audio to oscillate...oh never mind...it's too frustrating.

You're talking RF? So you mean that their is another transmitter operating on the same or nearby frequency. Yes I have heard of that. As an Extra Class ham op I am very familar with FM capture as well. On what station are you hearing this beat? In NY we have 4 HD stations and using multiple radios I hear none of the problems that othesr report. I will admit that at least here, the only HD directional station, itself 50 Kw, is a brand new installation and very well engineered. The other HD non D's are equally well engineered. The technology being relatively new for most of the engineers involved with it in the field has a deep learning curve and will require each engineer to learn the idiosicrities of his/her own system. Give these stations a few months to work out the bugs and over time these ills will disappear.

 

[davideduardo]

Exactly right David. I thought that's what I said. The problem is that in stations where maint. isn't all the important electronics drift and so you can hear the tones on the air. the tones might be sent at 0 or +4 and so after processing even a little tone leakage can be heard.

When I owend a syndication company, we put the tones on at -10 to a 0 db reference level. I think that was pretty much the industry standard.

 

[PhilJSmith67]

They sound to be as narrow as communication receivers.
Does either one have continuous tuning?

Both receivers appear to be narrow-band, like most of the AM radios on the market today. Both radios have digital tuners that only tune 10kHz increments. I am sure the Nissan has a conventional front end/IF/detector. I don't have a schematic to confirm this, but I was told that the Blau Digiceiver "SHARX" DSP circuit is only used for FM, and that the AM side uses a conventional IF/detector, with a digitally-tuned oscillator just like most other car radios.

This morning I drove from the the Crete/Beecher area to University Park, which is obviously farther from WGN than my last "tests" along I-290, and somewhat closer to WLW. This area is about 230 miles from WLW, and between 35 to 45 miles from WGN.

I was able to listen to a noisy but very much audible WLW the entire way, with WGN firing up the IBOC running-boards half way during the trip. WLW sounded identically weak but audible before and after WGN fired up IBOC. I wish I had a viable means of recording the entire event. I have a newer camera, but the audio quality is too poor to be able to tell the difference between IBOC interference or normal background noise, in cases where the two might be discernable in person. I've heard IBOC interference to second-adjacent AM stations on two of my cheaper home receivers, as well as a communications receiver with the selectable IF bandwidth set to 12kHz, so I am very familiar with what it sounds like.

As for WMT, it sounded as good as it possibly could for a station 210 miles away. But, it isn't fair to compare the effects of 620 WTMJ on 600 WMT or 640 WMFN this far south. The WTMJ IBOC sidebands are too weak here to have potential effect on any frequencies other than 610 and 630.

 

[PhilJSmith67]

As for the first adjacent channels on AM, I saw several posts on this board and another board that the sidebands on AM are too weak to interfere with anything because they are 100 times weaker than the main carrier. That is correct for the average IBOC power levels on FM, but not AM. Check the waveforms right in the iBiquity HD Radio AM spec. The primary ensembles, which are farthest from the center carrier, are quite potent. On the Nissan and Blaupunkt receivers, IBOC on first-adjacents just about blows me out of the car.

Tonight I was tuning across the AM dial on my Sangean HDR-1 just after sunset (CDT) while 850 KFUO from the St. Louis market was still on, with IBOC. As KFUO rolled in stronger and stronger, 840 WHAS and 860 CJBC became covered with interference. I could not lock the KFUO HD Radio signal, either. As soon as KFUO signed off at 8pm CDT, WHAS and CJBC cleared up immediately, and were strong. It was a little discouraging to witness how badly an IBOC sideband could interfere with relatively strong signals.

I have a few local stations here that have the same signal level as CJBC right at this moment. I wonder which of these stations I will still be able to listen to once nighttime IBOC is a reality. 770 WABC is booming in, with a signal rivaling 780 WBBM. I'm making a wild guess that WBBM will sound awful once WABC puts HD Radio on at night, and the analog WABC signal on 770 will render WBBM's IBOC signal useless (not to mention that 770 will also host part of WJR's IBOC signal). The background noise will rise and fall with DX, and the HD Radio signal will lock and unlock repeatedly. It's just not going to be a good scene for a lot of people, not until a lot of AM stations go dark permanently. :-\

 

[Tom Wells]

They sound to be as narrow as communication receivers.
Does either one have continuous tuning?

Both receivers appear to be narrow-band, like most of the AM radios on the market today. Both radios have digital tuners that only tune 10kHz increments. I am sure the Nissan has a conventional front end/IF/detector. I don't have a schematic to confirm this, but I was told that the Blau Digiceiver "SHARX" DSP circuit is only used for FM, and that the AM side uses a conventional IF/detector, with a digitally-tuned oscillator just like most other car radios.

This morning I drove from the the Crete/Beecher area to University Park, which is obviously farther from WGN than my last "tests" along I-290, and somewhat closer to WLW. This area is about 230 miles from WLW, and between 35 to 45 miles from WGN.

I was able to listen to a noisy but very much audible WLW the entire way, with WGN firing up the IBOC running-boards half way during the trip. WLW sounded identically weak but audible before and after WGN fired up IBOC. I wish I had a viable means of recording the entire event. I have a newer camera, but the audio quality is too poor to be able to tell the difference between IBOC interference or normal background noise, in cases where the two might be discernable in person. I've heard IBOC interference to second-adjacent AM stations on two of my cheaper home receivers, as well as a communications receiver with the selectable IF bandwidth set to 12kHz, so I am very familiar with what it sounds like.

As for WMT, it sounded as good as it possibly could for a station 210 miles away. But, it isn't fair to compare the effects of 620 WTMJ on 600 WMT or 640 WMFN this far south. The WTMJ IBOC sidebands are too weak here to have potential effect on any frequencies other than 610 and 630.

Well, I guess, it's just I've never been accepting of narrowband unless I'm looking at my 390.
Otherwise, everything AM BC I own is good to 15 Khz, or I've made it so.
I always favor continuous tuning, and all my car radios have TRF AMs.
Only the Blaupunkt, from 1982 has capactive tuning. The others, all factory radios, have superior inductive tuning.
They seem to be about 25 khz effective IF bandwidth, except for the Blau, which is 20 Khz IF with steep skirts.
All of the factory radios have had the upper end "opened up" in the audio, and the Blaupunkt was hi-fi AM originally.

With the additional mileage, and the narrow IF, I believe you.
In narrowband, the Sangean 803 did not show sideband products themselves between 696 to 704 khz, only an elevated background.
If I could hear the carrier, you probably could hear the analog signal.

But as I imagine from what I hear, I'd be using the 390 set to 4 kc ( it says "kc")or 2 kc if I were trying from your location.

Last fall, KFUO was over 100 khz wide with some "sparkles" in HD, I was working about 2 miles away, and called the engineer.
He couldn't get it to decode anywhere at all, so they took the HD off. They must have corrected the problem.
I wonder if the paint on on the tower base insulators were part of the problem?