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APRS Satelite Link Budgets



Since we hope to use the Kenwood D7 and D700 and maybe the Alinco
digital radios as mobile/handheld satellite terminals, and their
antennas in this situation are well known, we can put together
the following link budgets for using these radios as Satellite Message
Transceivers for our 3 Watt 2meter 1200 baud APRS Satellite downlink.

RANGE   ELEVATION  SIGNAL  D700 Mobile  D7A Stock whip  D7A w 19" whip
------- ---------  ------  -----------  --------------  --------------
 700 mi    90 deg   -101     22 dB            10 dB           16 dB
1000 Mi    45 deg   -105     18 dB             6 dB           12 dB
1500 mi    25 deg   -108     15 dB             3 dB            9 dB
2000 mi    10 deg   -111     12 dB             0 dB            6 dB
3000 mi    <5 deg   -114      9 dB            -3 dB            3 dB

These are margins *above* reliable packet decoding.

CONCLUSIONS:  

1) A mobile (assumed 3 dB gain whip) will get its messages even through a
   tree or two all the way down to the horizon.  At 45 degrees, it can
   stand over 18 dB of atteunation and still get its message.  Can be
   parked under a roof... or two.

2) D7A with good whip can do almost as well.  SHould be able to get
   your messages inside your house on most passes
 
3) Stock antenna should be able to get its messages if he can see
   the sky above about 10 deg.  Or can even get his messages with the
   radio in his pocket on passes above 45 deg!

I need to double check the Elevation angles above for  our orbit.
But the Link budget values should be pretty good.  The next level of
detail would be to match this with the gain plot of a typical
mobile antenna.

The goal is to get 2-way worldwide handheld satellite communications
anywhere a few times a day...  

One more thing.  SInce with APRS, the SATGATE computer KNOWS where you are
and WHERE The satellite is, it won't waste bandiwidth transmitting your
internet linked messages to you until the geometry is such to optimize the
link to your given antenna and location.  This system can just be so cool!

de WB4APR, Bob
See APRS on Satellites http://web.usna.navy.mil/~bruninga/astars.html


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