WFM in Air band spectrum?

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jryx
Posts: 3
Joined: Mon Dec 31, 2018 12:48 am

WFM in Air band spectrum?

Post by jryx » Mon Dec 31, 2018 1:47 am

Hello,

I'm pretty new to sdr and just get started messing around yesterday. I found a popular FM station transmitting on 111.65 MHz that usually transmits on 107.9 MHz. Is this unusual or is it normal to find stuff like this?

Actually, after writing this, I realized as I move around the spectrum I'm looking at the frequency of this station changes. As I get closer to fm broadcast spectrum, another station shows up, and the 107.9 station shows up at multiple frequencies. What is the cause of this is? I'm using SDR# by the way.

Thanks!

rtlsdrblog
Site Admin
Posts: 2237
Joined: Mon Nov 19, 2012 11:54 pm

Re: WFM in Air band spectrum?

Post by rtlsdrblog » Mon Dec 31, 2018 4:20 am

That's just imaging from the station overloading your dongle.

Strong stations will overload the 8-bit ADC on the RTL-SDR, causing images of it to show up at other frequencies. To stop that problem, reduce the gain, use filtering, or purchase a more expensive 12-bit or higher SDR.

jryx
Posts: 3
Joined: Mon Dec 31, 2018 12:48 am

Re: WFM in Air band spectrum?

Post by jryx » Mon Dec 31, 2018 9:40 pm

Ah, I see. Thanks for the info! I've seen FM filters on Amazon, and I'm guessing this is what those are for. Thanks again!

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