A question about FM frequencies

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lpff
Posts: 1
Joined: Sat May 02, 2015 6:31 pm

A question about FM frequencies

Post by lpff » Sat May 02, 2015 7:00 pm

Hello, I've started this month with SDR.
I'm using a Chinese dongle with my Note3 and I use SDR Touch app.
I'm interested to hear air-band and the configuration works very well, as I can listen the airport tower from 25km away and behind a mountain.
Scanning lower frequencies, I accidentally found that I can tune the normal FM stations (78-100Mhz)
in frequencies between 23-27Mhz. I'm also getting RDS (see picture).
Can someone give an explanation?
Many thanks
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rtlsdrblog
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Posts: 2873
Joined: Mon Nov 19, 2012 11:54 pm

Re: A question about FM frequencies

Post by rtlsdrblog » Sun May 03, 2015 10:13 pm

This is pretty normal. It's usually because the broadcast FM stations in your area are so strong that they overload the device causing images of those signals to show up on other frequencies. You can get rid of them by using a cheap broadcast FM-trap to attenuate the strong FM signals. Something like this should work: http://www.mcmelectronics.com/product/D ... 88-/33-341.

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