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[aprssig] Field Day ISS APRS Contacts? Doppler

david vanhorn kc6ete at gmail.com
Thu Jun 21 22:38:38 UTC 2012


Perhaps I misread, I thought Bob was saying that as the sat approached, the
RX doppler was higher than nominal, AND at the same time the TX was lower.
The doppler effect does not know which end(s) are moving, it is only about
relative motion, so as the distance is decreasing, doppler shift is always
up  and as distance is increasing doppler is always down, regardless of who
is speaking.

RX 437.560  TX 437.540  Approaching

So the sat is far away, and the relative velocity between it and me is high.
So my TX gets upshifted by some amount as seen by the sat. (matches
earthbound experience with train horns and such)  but so does the sat TX,
appearing higher on the dial than it would if we were both at rest with
respect to each other.  The above has me looking for the sat tx frequency
LOWER than nominal, when the doppler effect will be pushing the sat tx
frequency higher.

How could it be different?

The table makes no sense to me.   The frequencies should be the same for RX
and TX, just shifting through the appropriate memory as the sat approaches
, and then recedes.
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