What causes this "flutter" on FM signals?

[kkn50]

What causes this "flutter" on FM signals? I have heard it during tropo openings on FM Broadcast, VHF High Band. Heard this today on 30.300 mhz during an E skip opening. Here is a link to the audio file:

30.300 (OkieSam)

Thanks.

 

[Robinsmark]

FM Flutter

I don't believe that it is aurora, what you provided sounds like multi-path, although I could be wrong. Years ago GE made a circuit in the MASTR 2 VHF mobile radio receiver that held the squelch open to help alleviate this.

http://forums.radioreference.com/images/icons/icon5.gif Robinsmark

 

[zz0468]

What causes this "flutter" on FM signals? I have heard it during tropo openings on FM Broadcast, VHF High Band. Heard this today on 30.300 mhz during an E skip opening. Here is a link to the audio file:

30.300 (OkieSam)

Thanks.

Sounds like some sort of multipath where multiple reflecting points are moving in relationship to each other. I've heard similar fading on paths known to have an airplane bounce component.

 

[nd5y]

I second the multipath reflection from an aircraft.

 

[rfradioconsult]

The correct term is Rayleigh Fading, very common especially on the 800 MHz band, at road speeds it can sound like a loose antenna connection.

Rayleigh Fading :: Radio-Electronics.Com