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Re: APRS Satellite Details



On Tue, 12 Dec 2000, Timothy J Salo wrote about the Naval Academy's
satellite design:

> A satellite design optimized for specific models of one vendor's
> amateur radio equipment?

Yes and no.

It is an amateur satellite design with the primary mission to do two-way
digital messaging to handhelds with stock rubber duck antennas. (Sort of A
Ham radio digital Iridium).  We will optimize the digital waveform to work
the best we can with whatever handheld digital transceivers are available.

Right now there is only one, the D7.  As soon as there are more, we will
be delighted to optimize for the best fit to all that will be in use.

The mission for digital mobiles is secondary, because mobiles have a 10
dB advantage of Power and a few dB advantage of antennas on a car roof.
THus we have several dB margins here and have secondary receivers for
them (Also, UO22 and SO35 already fulfill this mission).

We took the approach that there are thousands of D7's in the hands of
amateurs.  These radios have everything needed to do a global handheld
amateur satellite communications mission.  Why not design a satellite to
take advantage of this situation?

My approach to HAM radio is to see what is available and then find a way
to use it to the best advantage.  And it does NOT HAVE TO BE NEW, nor
MANUFACTURED EQUIPMENT.  If anyone can identify surplus, scrap, or readily
available several thousand handheld trasnsceivers with built in modems,
displays and keyboard,  that can operate in the amateur bands with packet
radio then we will be more than happy to consider optimizing our satellite
design around them as well..

Or someone can design one that thousands of hams can build that will fit
in their shirt pocket or on their belt.  We will include it in our plans.

A satellite communications system is always designed as a system.  THe
user equipment is half of that system and is fundamental in the design of
the links.  WHen amateurs operate from .5 watts to 100 Watts with antenna
gains betweeen 0 and 16 dBi, the result is a difference in ERP of over
0.5W to 4000 watts.  We feel that satellite designs should always define
the target USER EQUIPMENT, design to that objective and publish that
baseline along with the mission.

Then request that users conform to the parameters of that mission as a
condition of operating it.  We have and will have plenty of satellites to
play with in space.  Rather than just throwing it up there and  then
letting HT's and KW stations duke it out..., we hope to establish a
precident in defining the user ERP and asking users to adhere to that 
uplink power.  If they do, then we think the satellite design will deliver
the advertised mission to the users...

de WB4APR, Bob


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