[amsat-bb] Re: Terrestrial QRM to FM satellites

Tony Langdon vk3jed at gmail.com
Thu Sep 20 15:17:30 PDT 2007


At 06:39 AM 9/21/2007, Scott Wilson wrote:

> > There are apparently several stations.
>
>How sure is everyone that the QRM is on the uplink frequency? I have
>noticed some QRM, but it's usually MUCH stronger than the downlink, and
>will almost always completely over power the satellite signal. I've just
>assumed that it's local 70cm activity from some locals who don't know any
>better.

Well, there are ways of telling.  Doppler shift is one.  Does the QRM 
follow the Doppler shift?  Then there's the issue of uplink 
interference.    If you have a keen ear, it is possible to tell by 
subtle differences in the audio whether the signal is on the uplink 
or downlink, especially when you're running headphones.  Similarly, 
it's also possible to tell if you are experiencing downlink problems 
or if the other station is not making the uplink, if you know what to 
listen for (without looking at the S meter).

The above (except for Doppler shift, of course) also apply to 
terrestrial repeaters.

73 de VK3JED
http://vkradio.com



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