[amsat-bb] Re: Doppler cancellation with 10GHz in-band channel.

[John <aa1ye@xxxxxxxxx>]

At 22:29 9/4/04 -0700, you wrote:
>
				snip
>
>KISS and build what works sounds good , but what about learning something
>new, and maybe advancing the state of the Radio Art? Have we forgot the
>purposes of Amateur Radio as outlined in Part 97.1?
>
>Nature is a balance. Hence why not something old, tried, and true? Plus
>something exciting, wild, and new?
>
>An in-band transponder for voice and data on the 10 GHz band would get my
>vote. With the 500 MHz bandwidth it could be done, and dish gain is not hard
>to come by at that frequency. 
>
>With 400 MHz difference the Doppler would
>almost cancel. 
>
	+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
										4 September 2004
	KC6UQH de AA1YE,
	Art,	

	Maybe yes, maybe no. 
	Doppler cancellation between two stations with the usual geometry will
almost certainly not cancel. You will receive your own D/L signal almost
free of Doppler since the two paths are just about identical. However the
other station will almost certainly have a different Doppler characteristic
to your signal. Hence there will be some differential Doppler on his signal
as received by you.

	However there is a (more complex) solution.

	If you include Doppler correction on your U/L signal, as can be done with
Uni_Trac, your frequency out of the satellite's transponder will be almost
constant. Adding Doppler correction to your received signal, your received
D/L signal will be nominally free of Doppler at your station.
	Provided the other station is using Doppler correction on his U/L signal,
his signal's frequency out of the satellite's transponder will be almost
constant. Hence D/L Doppler correction at your station will remove Doppler
frequency changes from both his signal and from your D/L signal as received
at your station.

	There have been several reports of very successful QSO during last
Wednesday's L-S band tests. Most stations used automated antenna tracking
and Doppler tuning; I know at least one station has FDT (Full Doppler
Tuning) capability with Uni_Trac and was probably using it for Doppler
correction on both his U/L and D/L channels. As a contrast, one station
reported his incredible ambidextrous agility of manually tracking and tuning!

	Operation as described above is not confined to an in-band repeater; a
C-band / X-band repeater (or another pair) will work just as easily when
both stations use a FDT aid such as Uni_Trac or similar "assistant" (or
ambidextrous roll-your-own).

	73s,   de  John  AA1YE.
----
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
Not an AMSAT member? Join now to support the amateur satellite program!
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org