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AM Interference Doesn't Have To Kill The Band: Expert
A consulting engineer is studying the problems of increasing interference on the AM band and says it doesn't have to be fatal. He claims there are solutions for a lot of the problems and one I found interesting is the perhaps impossible suggestion of not using 10 kilohertz spacing, to prevent interference from adjacent stations.
"The 10-kHz spacing we use is a century-old norm, but it results in “splatter” to your next-door neighbors. Over the years, changes in program content and audio processing have exacerbated this problem. I think that even with a minor change in occupied bandwidth, broadcasters can substantially reduce mutual interference and even improve their own audio."
He may be, as they used to say, closing the barn door after the horse has bolted, but it's nice that at least someone is trying to save the original broadcast band. My guess is that it's too little, too late, but I wish the guy luck.
Exploring AM Interference Issues
- Jody Thornton
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Re: AM Interference Doesn't Have To Kill The Band: Expert
But is that with less bandwith? How does 9 KHz spacing perform overseas?
I know that a lot iHeart/Clear Channel stations states-side limited their bandwidth to 5 KHz. I think that was done in the early 2000s, but if someone knows better, chime in.
Cheers,
Jody Thornton
- andysradio
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Re: AM Interference Doesn't Have To Kill The Band: Expert
I don’t see how changing the bandwidth will reduce radio interference much to the listener. In fact the change would render a lot of radios as junk especially in cars if the spacing was changed.
The main interference on the listener side is modern day electronics. On the broadcaster side, and this is applicable to the states especially, is that there are way to many AM stations. Many are zombie AMs being superseded by FM. If fully half of American AM stations went dark, interference would drop significantly.
- RadioAaron
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Re: AM Interference Doesn't Have To Kill The Band: Expert
As with the idea of expanding the FM band, even if possible and effective, anything that requires new radios will never happen.
- Jody Thornton
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Re: AM Interference Doesn't Have To Kill The Band: Expert
andysradio wrote:
I don’t see how changing the bandwidth will reduce radio interference much to the listener. In fact the change would render a lot of radios as junk especially in cars if the spacing was changed.
The main interference on the listener side is modern day electronics. On the broadcaster side, and this is applicable to the states especially, is that there are way to many AM stations. Many are zombie AMs being superseded by FM. If fully half of American AM stations went dark, interference would drop significantly.
I don't think they mean to redistribute the frequencies or change the frequency spacing. I was only asking about 9 KHz spacing overseas, because each station would occupy less bandwidth. I wondered if that affected reception there, but I don't think it's an even comparison.
However, reducing AM bandwidth would not obsolete current radios. In fact, with narrow band AM receivers that most of us have, you'd hear no difference. The response limit is usually 3 KHz at the best. Normally the only benefit for narrow bandwidth would be improved selectivity of a weaker signal, next to a strong one.
Cheers,
Jody Thornton
- Skywave
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Re: AM Interference Doesn't Have To Kill The Band: Expert
For AM, the occupied bandwidth is a function of the maximum modulating frequency, not the channel spacing. If you were to truncate the audio bandwidth sharply to 5 kHz, the sidebands would extend +/- 5 kHz, and the sidebands of 1st adjacent AM stations would not overlap. But you would also need to limit the intermediate frequency bandwidth of the receiver to achieve any real benefit.
Back in the early days of AM broadcasting, a common telco broadcast "twisted pair" connecting the studio to the transmitter was equalized to 5 kHz, so you had a virtual inadvertent limitation of transmitted bandwidth.
- andysradio
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Re: AM Interference Doesn't Have To Kill The Band: Expert
That makes more sense. Still the interference I contend with is not from 10kHz modulated adjacent AM stations.
- Skywave
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Re: AM Interference Doesn't Have To Kill The Band: Expert
There is a very recent NRSC report on noise in the AM band. See the key findings on page 51.
There is an interesting comment about noise from trolley wires even when trolleys aren't present. Recently I was driving on Eglinton Avenue where the LRT was doing test runs. I got a significant amount of hash on lower level signals like CKNT 960 even when the trains weren't moving
- jon
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Re: AM Interference Doesn't Have To Kill The Band: Expert
Skywave: similar situation in Edmonton. For both the former trolley lines (buses) and the current LRT system. Even when no vehicles in sight. Strongest memory was under a trolley line where CHED-630 was stronger than CFRN-1260 on 1260 KHz. Harmonic even though CHED's transmitter site was specially engineered to "eliminate" harmonics.