Hearing broadcast FM at 31.1 MHz with an SDR

[vpoko]

I'm brand new to radio, software defined or otherwise, so forgive me if this is a particularly stupid question. While listening with my RTL-SDR dongles, one E4000-based and the other an R820T, I can hear broadcast FM on 31.1. The station I hear on that frequency is 106.7, and both dongles pick it up. It's not the only FM station I can hear on frequencies too low for ordinary, broadcast FM. Why would I be hearing those there? Before I tried it with the R820T, I thought it must be an artifact of the SDR, since the E4000 can't go below 50 MHz, but they both pick up the same signal at the same frequencies, so I'm assuming it's really there.

 

[SCPD]

You are overloading the front end of the RTL set your gain to about 29.7 or less also turn off the RTL AGC and the TUNER AGC. Turn on OFFSET TUNNING

Hope this helps. You can copy the settings off my site in the rtl-sdr section

 

[vpoko]

Thanks! Good to know that's all it was. Is it strange at all that the two dongles, based on different chips, picked up the same station on the same wrong frequency?

 

[SCPD]

Did the new settings help?

 

[vpoko]

Did the new settings help?

I actually haven't been around to test it since I got the advice; I should hopefully be able to try it tonight and will report back.

 

[vpoko]

Yes, that does seem to eliminate it entirely. Very interesting, thanks!

 

[SCPD]

No problem. Overload was caused by the gain circuits being set way to high. Like i said before glad to help.