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*Subject*: RE: [amsat-bb] Trying AO-40*From*: "Howard Long" <howard@xxxxxxxxxxxxxx>*Date*: Mon, 2 Jun 2003 21:18:34 +0100*In-Reply-To*: <200306021933.h52JXLRw004246@ptialaska.net>

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 ---- 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

**References**:**Re: Trying AO-40***From:*Edward R. Cole

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