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Doppler Reality...

Hello All,

I want to address Doppler as it is applied.
Keeping it simple, without a lot of technical jargon.

On passes off in the distance, Doppler is less.
Picture a train whistle blowing.. we all have heard this before.
When it is off in the distance the pitch varies very little.
When a train is passing by you very close, you hear the whistle very HIGH in 
frequency, and as it goes away it goes LOW.
There is a BIG CHANGE in frequency when passing by..

Doppler on 2 meters is about 6kc, +3kc and -3kc on overhead passes.
However, Doppler on UHF (432) is about 20kc +10kc and -10kc.
When transmitting on 432 the Doppler frequency is changing pretty fast!
I use Ham Radio Deluxe (free) to adjust my TRANSMIT frequency ONLY.

Here is the kicker..... YOU, the receiving station still need to CORRECT the 
receive Doppler frequency even if the transmitter is correcting for Doppler.

Here is an example:

ISS is transmitting on 145.800
Transmitting stations can correct for Doppler so the receiver will hear 
within it's passband.
ISS's transmitting signal (constant frequency, 145.800) will shift +-3kc 
depending on the pass. You still need to receive the signal on frequency as 
YOU see it. It might be 145.797 to you, but to another station it might be 
145.803, depending upon the station's location.

So, adjust your TRANSMITTING frequency automatically if you can, so your 
output frequency will remain constant. Touch up your receiver to correct for 
normal VHF Doppler.

That is about in a nutshell....

I know many veterans of satellites may see this message as "stupid",
but there are a lot of new guys out there waiting to have you as their first 

73, and good luck!

Scott WA6LIE 
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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