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Re: Re: Full Doppler Tuning

>Jim wrote....
>>  Here is what I am doing:
>>1. Find the Beacon with the radio
>>2. enter the proper LO into NOVA, so that the actual predicted downlink
>>frequency matches the rig with doppler correction and 2401.323 entered at
>>the satellite. this turns out to be about 2255.999 990 for my UEK-3000.

Stacey wrote:

>As has been mentioned there is enough variation in the beacon freq. due to 
>spacecraft temperatures and downconverter drift, that it is virtually 
>impossible to implement a fully deterministic solution.
>Here's how I do it:
>1. Zero beat your signal on the downlink somewhere away from the beacon 
>(the software should get you close).

Stacey, Jim, others.

I do basically the same thing Stacey does and I use a "crutch" to assist in
taht same process...I developed a "no ditter" years ago for the low orbit 
birds, and a sample can be seen:


the file is noditter.zip

I think the pictured one is for FO29, but someone on here developed the same
thing for AO40, and inquiry on here will get you the url, or you can make your

I make one for each of the three down converters I use...Their frequencies vary
by ~50 kHz!  Temperature does affect that frequency so I encase them in a
1" thick styrofoam box to lessen the change rate with changes in temperature.
And I keep my preamp and converters powered all the time.  We only have about a
daily 10° temperature variation in San Diego, so I can imagine what happens in
other parts of the country with much more of a variation from daily high to
low.  When I suspected this I kept track of those changes over a period of 
without the styrofoam cover, and discovered that a rare rain shower 
contributed to
the change!

Add the above to the changes in the satellite, and that compounds the issue.
The no-ditter resolves all of these very easily, and one can tailor it to the
characteristics of your individual converter...

That's the reason I chose the Beacon+20 for the downlink for our net.  I've
been intending to conduct a survey of the uplink frequencies and/or the beacon
frequencies, just to get a handle on the variation, but we get gabbing, and 
many interesting things keep coming up!!

            73, Dave wb6llo@amsat.org
                    Disagree: I learn.... 

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