Topband: Alternating tone RFI

[wb6rse1 at mac.com]

I’ve also posted this on the RFI reflector.

I’m hearing a peculiar RFI tone on 160m and 80m. It’s two tones. One is a long tone with a short OFF. The other is approximately 13 kc lower and is ON exactly when the first tone is off. Sometimes the second tone appears plus and minus 13 kc from the longer tone’s frequency. I notice this every night but not until at least an hour or two after sunset. It’s not on in the early hours prior to sunrise. Signal strength appears to be directional. I’ve heard it occasionally on an upper HF band like 17m during the day but it’s much weaker.

I can’t find anything online that matches this description.

Any ideas on what to search for will be appreciated.

Steve WB6RSE