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Off Frequency AM stations

R

rtc

Hello,
In your DX travels have you ever encountered
an AM station that is off frequency?
A local is almost one khz off;Tom Servo relates
a somewhat distant station is regularly 2-3 khz
off...at first he thought it was European DX or
something.
In this day of GPS,PLL and such the idea of a
station being off frequency is unbelievable.
 
Lots of times. A few months ago during heavy auroral conditions, I heard an 1190 that was 100-200 hz off. Suspected XEWK Guadalajara, JAL which would've been a relog.
About a year ago, 900 CKBI Prince Albert, SK was a kilohertz off! Instead I was hearing a whining het on 900 and CKBI on 901 khz!
I don't hear them anymore, but I have heard a 940 that way was off as well. Believe that was XEMMM Mexicali. Never confirmed it.
 
KBSN 1470 in Moses Lake WA was off by enough hertz to put a good growl on the frequency for a while. I think that's been cleared up, though.

You probably remember that one, Crainbebo, I believe you first noticed it and mentioned it on the BCBLogger site.
 
How do you detect this, unless, say, you hear a 1390 on 1380 instead? I've suspected this about many AM stations but don't recall specific instances of hearing anything that clearly "off."
 
icybluelake said:
How do you detect this, unless, say, you hear a 1390 on 1380 instead? I've suspected this about many AM stations but don't recall specific instances of hearing anything that clearly "off."
Click to expand...

If there are one or more "normally" operating stations on the frequency, the one that is off will beat against the non-complying one producing an audible heterodyne equal to the number of cycles per second of the deviation. A heterodyne is produced by the effect of the two signals, the accurate and the deviant one, interacting.

This is, by the way, why the FCC specifies frequency deviation of less than what would be audible by anyone except a dog.

The higher the deviation, the higher the pitch of the heterodyne. It can be the low sub-woofer rumble of a station 80 or 90 cps off channel to the shrill whistle of ones around 1 kHz off.

Another way of knowing is with a more professional communications receiver or SDR receiver which may display the carrier channel down to 1 cps precision or better.
 
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