[amsat-bb] Intermod

[Jerry Pixton <jpixton@xxxxxxxxxxx>]

All,

Today I put the UEK-3000 on the back of the elevation rotor and moved the 
dish way over on the VHF side (almost to the elements). Increased the 
spacing from 44 inches to 89 inches. It did reduce the interference some 
but not much. Then I ran a test with the UHF transmitter feeding a little 3 
element yagi fixed on the horizon towards our local UHF repeater. This yagi 
is about 20 feef below the oscar setup. Still had intermod. So even big 
separation does not help. ?????

Second set of tests was to step up the UHF band in 1 meg increments. Steps 
430.5 to 434.5, 436.5 to 441.5, and 443.5 to 449.5 gave no interference. 
But steps 435.5 Mhz and 442.5 Mhz gave interference. Of course right in the 
satellite area.

Third test was to get some finer grain detail.  So I checked across the 
AO-40 passband.  Between 435.495 and 435.55 and from 435.625 to 435.700 I 
get interference.  But there are two strips from 435.55 to 435.625 and from 
435.700 to 435.800 that have no interference. The S band frequency was 
being tuned automatically as if I were using the transponder

The interference looks like a set of spurs (looking with ao40rcv) about 
1200 to 1500 hz apart (I can see several in the passband) when keying cw.

I pulled the cover off the UEK-3000 and see that the chassis is soldered 
shut. So I don't know what room is available for a notch filter.

I did also just run the FT-847 into dummy load just to make sure. When I 
turn off the power to the downconverter, the interference goes away. And 
when I turn the power back on, the interference drifts for a few seconds as 
the LO stabilizes.

At least there is a segment where voice could be operated and at the low 
end cw. The main group of spurs is around the beacon frequency anyway where 
I don't want to transmit.

And here I was going to play today building some helix prototypes. HI

Any thoughts.

Jerry, W6IHG
------------------------------------------
Dr. Jerry R. Pixton, PIXOS Designs LLC
http://www.pixos.com/designs/
jpixton@shentel.net
------------------------------------------

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