V - Free and Open Source Software

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H AMSATS·,mee",ooYO" , eeeee" '''d
AndyMacAJli$/er WASZIB
14714 Knigh/sway Drive
Houston TX 77083
Station Enhancement
Only 15 years ago most of the antennas
and accessories in an amateur
satellite station were hom.brew or
made from kils. Today the reverse is
true. Alilhe necessary gear can bepurchased.
but many amat8!Jrs prefer to
build their own preamp and antenna­
polarizatiOn control box.
Some salell,te antennas come wilh
poIarization.conlrol units. Of can be
purchased as an ophon. A. lew mastmounted
preamps come WIth control
boxes, but most do not,ln many cases.
stalions will haw 81leasl tour individual
COfItrol units tot the anlenna-mounted
2 meterand 10 em preampsand the
polarization relay5 on the antennas,
Newcomers may ask why mastmounll!'d
preamps and polarizationcontrol
oevices are necessary. 80m.
l imes they are nol. but amateurs who
have worked with the satellites for a
lew years know the advantages 01 having
them. Such systems are especially
useful for the high-o(1)it satellites, like
AMSAT·Q SC A R· l 0 and AMS AT·
OSCAR-13, where distances and sig.nal
attenuation are many times greater
than for the Iow-Clrbit satellites,
The schematic in Figure 1 ShOW1l a
simple control box that incorporates all
the necessary control functions with
the least number of parts, Most polarization
relays and remote preamps operate
from 12-14 volts DC, so any 12
VOC regulated supply capable of one
to two amps will provide power, If the
supply is home-brew, install a fuse with
the appropriate current rating on the
AC line. Commercial supplies should
already have a fuse.
The purpose of the simple design is
to give an easy-to-read and meaningful
indication of relay or preamp operenco.
The lirst LEO atler the power supply
is simply a power·on indicator,
while the second shows that lhe 12
VDC in-line luse is intact. The current
meter preoces the simplest means 01
monitoring the relays and preamps
wilh a true indicatiOn that the correct
current is being consumed by the
device or devices thaI have been activated.
Most poIarizaliOn relays draw about
100 rnA. When a line is energized, the
el(pected reading should show on the
meter without change. Loose eeeeeetions
are immediately apparent it the
readIng verses. A short causes spikes
and may even blow the fuse. but no
power supply oamage occurs and the
problem can be quickly resolved by
tracing the line to the antenna. Corrosion
over a period 01 years is usualty
the problem.
Mast-mounted preamps can draw as
little as 50 mA up loa lew hundred mAo
54 73Amateur RadiO roaev » June. 1991
AmateurRadio Via Satellite
aetcre they are installed, each polarizatiOn
relay and preamp in use should
be tested, and the current measured,
to characterize nominal consumption.
Labels on the control box for each line
are helpltJl. In a typical confoguration
with 100 rnA polarization relays and 50
rnA preamps, the current meter $I1Owf;
300 rnA when all the remote items are
activated. The extra line could be used
lor a 10 meter preamp in the shack.
Cable to the remote relays and units
should be good quality rotor cable or
old coax runs. Avoid cheap rotoe ceble-it
will .,.teriQrate with outside exposure
to the elements. Eight-eon