Satgen 517  Globalstar Sat Phones  by GM4IHJ  (BID SGEN517) 1999-02-20

The threat to the radio amateur VHF and UHF bands from constellations
of Low Earth Orbit (LEO) data and voice satellites is still uncertain,
but has certainly not gone away. Much may perhaps depend on how
successful the soon to be operational , higher frequency, mobile phone
LEO satellite constellations ( Iridium and Globalstar), prove to be. 

At VHF (137 MHz) the Orbcom LEO constellation of 28 satellites is
already operational in a store and forward ( no voice) mode. But the
Iridium network is having a rather shaky start . Still to come is the
Globalstar network which differs in some interesting ways from
Iridium. So it may be instructive to monitor Globalstar progress over
the next few months as the constellation is assembled and set to work,
to see how things develope.

As yet only two sets of Globalstar sats are in orbit in planes
separated by 42 degrees. Eventually 8 orbit planes will be occupied by
6 satellites in each plane, with orbital inclination of 52 degrees .
Orbit period is 111 minutes approx , putting the satellites up at 1200
kms average altitude ie much higher than Iridium . Individual
satellites will therefore stay in range of a particular station for
much longer than Iridium.

Operating Frequencies are :-

       1610 to 1626.5 MHz  handset uplinks
       2483.5 to 2500 MHz  handset downlinks 
       5091 to 5250   MHz  ground station gateway uplinks
       6875 to 7055   MHz  ground station downlinks

So unlike Iridium there is no downlink in the radio astronomy
sensitive region around 1610 MHz. Although this does make it more
difficult for radio listeners who want to monitor Globalstar setting
to work on standard receivers. 

There is however at least one solution to the reception of the handset
downlink. QST for February 1998 reported the availability of the Drake
model 2880 microwave down convertor. This is a surplus unit designed
for reception of local microwave distribution of television. With
local oscillator on 2277.9904 MHz , it covers reception from 2.4 to
2.7 GHz ie putting the Globalstar handset downlink out on a frequency
of 205.5 to 222 MHz , which can be received by several standard
general coverage all mode receivers such as the ICOM R7000 series and
the Yaesu 9600 models. Using this converter you will be able to judge
the level of user activity, but not decode the traffic.

On the internet, http://www.geocities.com/siliconvalley/vista/7012  
and others , contain useful data on modifying these converters for,
other frequencies , improved performance and, direct as opposed to the
existing "up the antenna cable" supply of DC power.