What's wrong with this NOAA transmission?

[Urbanexplorer]

I recorded this directly from weather radio to tape in the spring of 2010 while coming into Chicago.

I remember that our car was not moving while this was recorded, and that there was no severe weather of any kind.

I've had a few suggestions for the cause of the noise: radar noise, harmonics, a mic being keyed over the frequency...etc. Anyone care to hazard a guess on what's causing this noise?

http://k004.kiwi6.com/hotlink/679721n31 ... erence.wav

[md5]

Last time I heard a NOAA weather radio do that was KGG98 in Halls Summit, KS; it had maintenance on going at the transmitter tower. Usually due to the fact of them re-tuning the receiver. However with the off BZZZRRRR sort of sounds, I can't explain that.

[bwillcox]

The interfering signal sounds like P25 to me. Probably intermodulation distortion from another transmitter elsewhere in the band.

Compare it to http://www.dvara.org/p25/p25-undecoded.wav which is undecoded P25 as heard by an analog receiver.

-b-

[MARSAUTOSIREN]

My old RadioShack pro 2018 would pick this up when the signal crossed a digital path. Might be interference with a scanning frecincy.

[Urbanexplorer]

Might be interference with a scanning frecincy.

What do you mean, exactly?

This wasn't picked up using a scanner; I have a radio/cassette deck that have TV-L and TV-H bands on it.

[MARSAUTOSIREN]

Yes I know, but if one scanner frequency was being broadcast near the same frequency as the NOAA broadcast, it might interfere.

[guitarguy1985]

I have a radio/cassette deck that have TV-L and TV-H bands on it.

That explains it. TV audio is wider in bandwidth than some other broadcasts. So you could actually be tuned to a range of signals at the same time. I have an old black and white television that picks up NOAA broadcasts by tuning below channel 7 on VHF high, and the same thing happens. Every few seconds it is interrupted by a data signal of some sort. I'm not sure if NOAA broadcasts (and/or the interfering signals here) are AM or FM though, usually with AM you can get the audio from multiple signals at the same time, where as with FM the strongest signal wins.

[Urbanexplorer]

I have a radio/cassette deck that have TV-L and TV-H bands on it.

That explains it. TV audio is wider in bandwidth than some other broadcasts. So you could actually be tuned to a range of signals at the same time.

But in that case, wouldn't the signals broadcast simultaneously instead of one overpowering the other?

This is the only time I've heard this happen, and I've tuned in to NOAA stations all over the midwest.

[guitarguy1985]

Not with FM, because of the capture effect. Only one signal will be detected. Analog television uses AM for the video signal, but FM for the audio signal. The bandwidth for the audio signal is around 500KHz, I think, where as NOAA stations are spaced only 25KHz apart, very narrow in comparison.