Re: [amsat-bb] FT-847 AO-40 and Doppler Uplink Correction?

["Jens H. Jensen" <topcat@xxxxxxxxxxxxxxxxx>]

At 22:42 22-07-2001, you wrote:

>I hope this helps a bit.

Ok, Chris, but aren't you simplifying it a bit ?

What if we take the uplink as a reference:

Uplink frq = X (23cm)
Downlink frq = 2X (13cm)
Approximate frq's, without doppler, just for example!

Uplink at frequency X, doppler on uplink -10Khz (example!)
Uplink frq that the satellite sees : X - 10Khz Doppler

Transponder Inverting : receives 10Khz too low, becomes 10Khz too high on 
downlink after inversion (at the sat, before doppler)

Downlink frq about 2X (example) + 10 Khz - 20Khz doppler (because downlink 
frq twice as high)
Downlink frq that the uplinking/downlinking station sees/hears : 2X - 10Khz.

This will look (subjectively) as half the doppler, compared to a one-way 
downlink (beacon).

Doppler subtracts here (subjectively, seen from the rx/tx station), as 
opposed to an non-inverting transponder, where it would ADD. ??
I reckon this is the reason for the invention of the inverting transponder, 
or are there other reasons?

Anyone more experienced have a comment?

73 de OZ1LRG

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