[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: so35



On Tue, 6 Jul 1999, KF4FDJ (Mike in Ft. Myers, FL) wrote:

>...  However, apparently you don't operate ALL of the LEO birds....
> 
> Bob Bruninga wrote:
> > Having completed a weeks worth of HT testing via MIR using rubber ducks
> > and being 100% successful, and having done the link budget, there is
> > absolutely no need for any power over 5 watts on ANY OF THE BIRDS except
> > AO-10.  The problem is congeston.

Mike is right,  My over simplification was based on the assumption that
all of the satellites would run with a nominally sensitive receiver.  The
Link between two nominal FM rigs running  just over 1 watt to Dipole
antennas will cover 2000 km on 2 meters.  On 435 Mhz it takes about 10
watts for the same path and dipole antennas.  THus it is easy to build a
satellite that can be used by anyone with 5 watts on a 2 meter uplink and
still have a 6 dB margin.  Mir is a perfect example of a "nominal"
receiver.  All of the PACSATS, MIR, AO-27 and others have such a nominal
sensitive receiver.   But there are also good reasons not to have maximum
sensitivity such as on the RS Analog birds.  And the antennas are never
perfectly aligned.

But any LEO satellite will show over 10 dB difference between someone on
the horizon at 2000 miles and someone underneath at 600 km.  Thus the guy
on the east coast who wants to work the LEO over California will
need to run 50 watts to equal the calif 5w stations and will need to run
8 elements to win.  In HAM radio, lots of folks with roof mount
antennas want to work the bird horizon to horizon.

Yes, my bias is encouraging mobile satellite operations and in this case,
it makes no sense to add the 10 DB of extra power to work down to the
horizon, when 99% of all mobiles cant see the satellite below say 10
degrees...  

Mike is right that I have not worked the RS birds. They will surely have
lower gain front ends to preserve linearity in an analog transponder and
so much more power is required.  But that is exactly my point.  Why does
not each satelite publish the required ERP?

Just because a few satellites do require high power and gain antennas,
I am only suggesting that those arrays and power may be overkill on many
of the other birds.  All of the satellites I deal with professionally have
a published ERP threshold.  THus there is never any question as
to what is the right power to run under what circumstances.

There is no one answer for all circumstances.  But published ERP's or
even better, published Satellite receiver sensitivity thresholds would
sure make for a better informed user base...

bob, WB4APR



----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home