[amsat-bb] Re: Increasing range from LEO

[Patrick Green]

Why is pcsat having so much trouble carrying its 5 watts then?  Even  
when the satellite is in full sun?  Even on the Z panel?  I'm not  
complaining, I just want to understand what went wrong.

73 de KA9SCF.

On Sep 3, 2009, at 17:34, "Robert Bruninga" <bruninga at usna.edu> wrote:

>> To get good coverage you need as many
>> LEO satellites as possible so they should
>> each be as small as possible.
>> Intersatellite linking could be done
>> via automated ground stations. This
>> eliminates the need for high-power
>> transmtters and/or high-gain antennas
>> on the satellites for interlinkng.
>
> Yep, that is what we have been trying to do now for 8 years with
> the APRS satellites on 145.825.  We just need several of them in
> orbit at the same time.  We have demonstrated dual-hops several
> times whenever two or more of the APRS satellites (and ARISS)
> are operational at the same time.  If we could get 6 to 10 of
> the University cubesats to simply carry the 3.4" square APRS
> transponder (Byonics TinyTrck-4), then we would have a
> constellation providing nearly continuous connectivity via these
> satellites from any handheld or mobile APRS radio.  With 6, you
> might have to wait 30 minutes or so to make yoru contacts.  With
> 10 or so, you might have to wit no more than 5 to 10 minutes for
> connectivity.
>
> See www.aprs.org/cubesat-comms.html
>
>> It's better to put that gain and power
>> consumption on earth.
>
> The advantage of the APRS satellite concept and Packet, is that
> we can use a 5 Watt transmitter on the satellite to be able to
> hit any mobile or HT using its existing omni antenna because the
> packet has a low dutycycle.  So running 5 watts on a cubesat is
> easy, because the transmitter dutycycle is only on less than say
> 5% of the whole-orbit time. (average power 1/4 Watt)
>
> Whereas ECHO which is on all the time, has to be set at 1/4 watt
> TX power because it is on all the time.
>
> Also, EVERY APRS satellite would be on the same frequency
> 145.825 with no doppler to track, and since every one of them
> does the same generic relay, independent of callsign, then the
> user on the ground just operates... He does not have to do
> anything to go from one satellite to another...
>
> Bob, WB4APR
>
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