SOLVED: Identifying interference with oscilloscopes and software-defined radio
#15
Exclamation A discovery.

I found the source of my 60 kHz interference - it is actually the atomic time station WWVB.

I figured this out by listening to the signal in GQRX. I tuned in and listened in single side-band (SSB) mode, and realized that it sounded like an on-off-keying modulated signal.

I then looked up a list of very low frequency (VLF) stations, and found this very useful page: http://www.mwlist.org/vlf.php There are three stations listed that transmit at 60 kHz, particularly WWVB, which is located in Fort Collins, Colorado and transmits at 70 kW. I live in Spearfish, South Dakota, which is about 240 miles away. There is no doubt that I should receive this station loud and clear.

A quick test confirmed my suspicions.. I rotated my ferrite antenna and watched for the signal to null out. Sure enough, when I pointed the axis of the ferrite stick in the direction of Fort Collins (my south-southwest), the signal disappeared. Mystery solved.

The Wikipedia page about WWVB is an interesting read. This station transmits the signal that most radio-controlled clocks in the US use to synchronize their time. You can listen to what the transmission sounds like in this YouTube video.

Anyway, it took me a long time to figure this out... I bet any old Ham operator worth his salt would have known right away.

I suppose I'll install the low-pass filter ICs on my receiver to block this station.

Now I'll try to figure out the origins of the 25 kHz signal. That one definitely sounds like electrical noise..
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RE: Identifying interference with oscilloscopes and software-defined radio - by djhuft - 2017-08-11, 02:51

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