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Echo Ground Station Simplicity!



On Fri, 20 Jun 2003, Rick Hambly (W2GPS) summarised ECHO's features:

> . Mode V/U, L/S and HF/U.  Also V/S, L/U and HF/S sometimes....
> . Analog operation including FM voice.
> . Digital modes. Store and forward. Bauds of 9.6, 38.4, 57.6, 76.8
> . PSK31 repeater using 10-meter SSB uplink and UHF FM downlink.
> . Four VHF receivers and two UHF high power 8-Watt transmitters.
> . Multi-band, multi-mode receiver.  Analog and Digital simultaneous.
> . Can have geographical personalities.
> . Digital Voice Recorder (DVR)

This is FANTASTIC!

Although I frequently post about the 9 dB benefits of operating Mode-B
for EASY sats 'to-omni-antenna-users', I must point out, that all of that
advantage is lost -IF- one decides to use a small UHF beam.  THis is an
important thing for everyone to understand.

Now, since ECHO is to be a super-satellite, and since half the 'fun' of
operating satetllites (and using them in education about satellites) is
to POINT something at them, then Mode-J is EQUAL to Mode-B.  This is
because a Handheld 4 element UHF beam is about the same SIZE as a VHF
omni, so this balances the LINK budget using antenna size as the
comparison.

Now, another IMPORTANT thing that often gets overlooked is that it does
NOT take an "OSCAR" array with AZ/EL rotators to work a mode-J LEO bird!
It only takes a $60 TV antenna rotator and a small 4 to 7 element UHF
beam the hear ANY mode-J low-earth orbiting satellite.  We do ourselves a
disservice by implying that every satellite operators needs an OSCAR
array.

A small 10 dB gain UHF vertical beam canted up at about 10 degrees from
the horizon can work  ALL terrestrial uses of 440 as well as work all
the LEO satellites perfectly well.  Remember, you only need gain on the
horizon where the satellite is 10 dB further away and spends 70% of its
time.  When it is above 45 degrees (5% of the time) it is 10 dB stronger!
See the table on http://www.ew.unsa.edu/~bruninga/rotator1.html

We need to make sure the membership understands that ECHO will not need
an OSCAR array, and in fact a TV rotator and a small UHF beam is perfect.
ANything BIGGER just makes the beam narrower and tracking harder...

Of course, with 8W of power, ECHO will also be able to communicate
DIRECTLY to stations with an OMNI antenna under those modes when all the
power is dedicated to one or two downlinks too.  But I think it will be
better to have several modes running at the same time sharing the power to
let more people use it at once.

So make sure you have a working TV rotator.  In a few years you might
not be able to buy them as everyone wants you to go cable and satellite and
fiber...

de WB4APR, Bob


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