[amsat-bb] Mac Doppler

[Joe]

aHHH tHAT MAKES TOTAL SENSE TO ME NOW!

jOE wb9sbd

opps cAPLOCK

He is thinking on getting on the birds and asked me to help because I 
did do it many many years ago. he just bought a 9700. so is all excited.

Any suggestions to send to him as to what birds to shhot for as well as 
antenna systems?

Joe WB9SBD

On 7/10/2020 6:59 PM, Paul Williamson wrote:
> MacDoppler is correct.
>
> Doppler shift changes the effective frequency of a radio signal in 
> transit. When the satellite is coming toward you, the frequency of 
> both the uplink and downlink signal is increased by Doppler shift. The 
> goal of the computerized tuning is to maintain a constant frequency 
> *at the satellite*.
>
> So, consider first the uplink (your transmitter), and assume the 
> satellite is coming toward you. The computer needs to shift its 
> frequency DOWN, so that after Doppler has up-shifted the signal it 
> will arrive at the satellite on frequency. Now consider the downlink. 
> That is, the satellite’s transmitter (your receiver). That signal is 
> where it is, when it leaves the satellite. Then it gets shifted UP by 
> Doppler. In order to receive this signal, your receiver will need to 
> shift UP to match. Thus your two radios need to shift in opposite 
> directions to compensate for Doppler.
>
> Note that this is independent of whether the transponder is inverting 
> or not.
>
> For some discussion of why the goal has to be constant frequency at 
> the satellite, see my ancient article on The One True Rule for Doppler 
> Tuning, presently hosted at https://www.amsat.org/tag/tuning/
>
> 73 -Paul KB5MU
>
>> On Jul 10, 2020, at 4:27 PM, Joe via AMSAT-BB <amsat-bb at amsat.org> wrote:
>>
>> A buddy of mine just installed MacDoppler
>>
>> It seems to work great but he sent me a video that doesn't make sense 
>> to me.
>>
>> It is controlling his radio changing freqs as needed to account for 
>> Doppler.  BUT... I have never seen this before.
>>
>> the 144 band was changing one way in freq and the 440 band the other 
>> way.  Huh? That doesn't seem right in my head.
>>
>> anyone care to maybe explain whats happening?
>>
>> Joe WB9SBD
>>
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