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[aprssig] Satellite positions: FREQUENCY

Lynn W. Deffenbaugh (Mr) ldeffenb at homeside.to
Tue Oct 18 23:10:33 UTC 2011

On 10/18/2011 1:20 PM, Heikki Hannikainen wrote:
> I believe that's not quite true? The distance is going to be 
> incorrect, and the elevation will not be shown (the mobiles/ht's don't 
> calculate that for you, and I don't know if they even could, does the 
> altitude format do big enough numbers anyway?).

Altitude only goes to 999,999 feet, and isn't much use as compared to 
Elevation in degrees above the horizon.

> The bearing can be transmitted in the message without worrying whether 
> the position packet makes it through. If the satellite is not 
> currently in view, the user probably wants to know the bearing where 
> the satellite will appear at the time of the AOS. He couldn't care 
> much about the *current* bearing unless the satellite is visible 
> currently.

AOS bearing, according to Bob's recent comment about mobiles not being 
able to copy until well above the horizon, seems to be useless as well.

I still believe that the best possible use is to query when you think 
you've got time to work the satellite.  If there's one in range (and 
high enough) great!  You got lucky so work it.

If you didn't get lucky, make a mental note of the delta time from now 
and if you think you might be available then, send another query to 
re-confirm when you're ready to work it.  You don't need to fiddle with 
the stored messages (which may have been from days ago with no way to 
know that), just query and you'll know the current situation along with 
the Az/El if you're actually within the pass.

Two messages spaced across time is, IMHO, much better than a message 
with (non-date-stamped) zulu time with a "courtesy" position packet 
meaning the operator needs to check TWO lists, the message list and the 
station list.  If we just stick to the messages, there's only ONE 
message packet when the operator needs/wants updated information.

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

PS.  And it's NOT only useful for mobiles.  Anyone sitting on APRS, RF 
or -IS, radio, PC, or mobile platform, that is just bored can send the 
query to see if it's worth firing up their satellite prediction software 
now, or later.

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