RE: [amsat-bb] Trying AO-40

["Howard Long" <howard@xxxxxxxxxxxxxx>]

Hello Ed

> That is why the circular calculator is so nice....it estimates satellite
> Doppler as a function of MA.  What I haven't seen discussed here is the
> fact that not only is there Doppler due to the orbital movement of AO-40
> but there is earth rotational Doppler and all Doppler effects vary with
> your latitude.  The circular calculator probably doesn't take into account
> earth rotation so there is a small error due to this.

Actually, it does :-) You'll see that it's not symmetrical around MA=128:
it's actually symmetrical around MA=131. That's because the way I calculated
it was to average the Doppler difference from five consecutive orbits using
a prediction program. But, as my notes on the page suggest, you're on your
own at about MA<15 and MA>240! That needs a bit more than a couple of
cardboard disks to calculate. Fortunately, that is not a big deal because
it's usually the least useful part of the pass from an operating
perspective.

> Also we are only
> taking into account S-band Doppler and your uplink has Doppler too.  The
> complete mathematical problem is pretty complex!

The 70cm uplink offset was also taken into account when making the disks.

> Fortunately, 70cm Doppler
> effect is much smaller so one can usually find themselves quickly if they
> have the S-band tuned in.  L-band will have three times higher Doppler
> effects!

There is an L/S band version but you are right it is not as accurate.

> K-Band is really a difficult one!!!

The drift on my LO at K band is so large that I figure I'm wasting my time
trying to figure it out with this paper method!

As others have alluded, the quick and dirty way is to find the beacon, set
your U uplink to 435.666, switch on reverse tracking, then move away 20kHz
or so to find yourself. (L band is 1269.388 for this trick). But I hadn't
figured that one out at the time I made the disks...

73 Howard G6LVB

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