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Re: Elevation-dependent Interference



Hello Greg,

Consider water in connectors, water in downconverters or preamplifiers, 
water in cables.
    water in feed systems and baluns. If water is a problem, frozen 
water,  hard and fixed in place ,
    would probably give different symptoms than sloshing liquid water.

Consider loose connections on the antenna, where it is hard to inspect. 
or at coaxial joints.
    Broken connections due to birds... or thermal stress.

Consider the binding of cables that may be stretched/deformed at one 
elevation and not at another.

Consider other masses of metal in proximity to the offending antenna at 
different elevations.

Yagi antenna should be free and clear of any near by metal for multiple 
wavelengths

Would a tight bandpass filter help on the TX side ?

Stan, WA1ECF





Greg D. wrote:

> This is weird.  Do I have defective foliage, or is this
> to be expected?
>
> I've been having trouble with desense on AO-40.  Transmit
> on 70cm, and the 2.4 ghz noise floor rises so far I can't
> hear anything else.  Found some bad connections and a bad
> set of relay contacts; thought it was fixed.  But earlier
> this week it came back.
>
> After some experimenting, I find that as the Elevation
> heads towards the horizon, the desense problem rises.  As
> the elevation rises, the problem goes away.  Above about
> 20 degrees, it's essentially gone.  Nice and smooth (not
> due to a bad cable at the rotor).
>
> Now, this isn't the ground (thermal) noise I'm picking up.
> It's only there on transmit.
>
> Any ideas why this is happening?  Any fixes?
>
> Greg  KO6TH
>
>
>
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