SOLVED: Identifying interference with oscilloscopes and software-defined radio
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: 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..

Messages In This Thread
RE: Identifying interference with oscilloscopes and software-defined radio - by djhuft - 2017-08-11, 02:51

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