[amsat-bb] Re: ECHO

Colin Hurst cjhurst@bigpond.net.au
Fri Aug 25 22:51:44 PDT 2006

May I take some of your time to educate you on the reception of AO-51.
First I will address your comments.
The supposed flea power from my understanding is to ensure the batteries
on board AO-51 remain charged to optimal conditions to achieve longevity.
The downlink power is not a mystery as it is embodied in the telemetry.
If you are unable to copy the telemetry, all you need to do is politely
enquire on the amsat-bb. The power levels change rarely, except for special
events, tests, whatever.
I believe AO-51 has been published technically to a high standard.
There is a huge amount of information on the Amsat-NA web-site.
Do own a copy of Gould Smith's excellent publication?
Now to reception of AO-51.
Personally I have been monitoring AO-51 since launch, downloading and
analysing telemetry, which is my particular "focus".
There are many orbits I could also "shout from the rooftop" as being very
poor reception. However over time I have built a profile for reception
at this QTH. I know those passes that will provide excellent copy and those
that leave much to be desired, albeit I operate a fully automated station.
What are some of the influencing factors.

Foliage is a very well documented attenuator of 70cm signals.
Australian Eucalypts to my west attest to that.

Polarisation changes occur as AO-51'a attitude varies (below).
Although AO-51 is circularly polarised, there will be occasions that
or Horizontal  polarisation is strongly evident by the observer.
This is important to users of dedicated vertical or horizontal antennae.

Because AO-51's attitude is magnetically stabilised using passive magnets,
there will be occasions when the antennae are not earth pointing, hence
you may experience shielding of the antennae. Theoretically the northern
hemisphere is least affected, but there will be occasions when the
of the earth's magnetic field may give it an extra kick and degrade
for that particular orbit. Surprising what you can observe by just
Signal strength, rate & depth of QSB, signal reports being given by other

You state you have an 8 element yagi with a preamplifier.
Is the preamp located at the antenna feed point?.
If not, it should be for optimal performance.
This is the most significant way to improve station performance.

Is the antenna auto tracking in az & el?
If so, is it tracking correctly?
High winds moved the rotator on its mount (personal experience).

Whatever your station setup, I strongly recommend that you build up a
reception performance profile, over a substantive number of passes.
Forget about the TX, just listen with the objective of reception
By recording strength of signal, pass elevation, whether east or west,
local QRM,
magnitude of QSB, foliage present etc. you will quickly establish what are
your optimal passes, those not optimal.
I monitor many satellites.
They all have strengths, weaknesses and peculiarities relative to my QTH.
If we always had "arm-chair" copy the fun and challenges would quickly
There is always room for improvement, especially reception performance.
Colin VK5HI.

> -----Original Message-----
> From: amsat-bb-bounces@amsat.org [mailto:amsat-bb-bounces@amsat.org]On
> Behalf Of McGrane
> Sent: Friday, 25 August 2006 22:57
> To: Amsat BB
> Subject: [amsat-bb] ECHO
> greetings
> I would like to report very poor reception of echo even with an 8 element
> yagi and an 18 Db preamp. I assume the downlink power is real flea power
> for battery charging or other testing.
> After 2 years of pleading with amsat, the downlink power is still a
> mystery. It is not shown on the colaradosatellite telemetry graphs (TX B)
> or the amsat website, after repeated requests here and elsewhere I'll
> assume it is being held secret for some reason.
> There has been a tremendous lack of technical reporting on ECHO.
> I realize people are very busy but time should be taken to educate the
> amsat community.
> 73, patrick N2OEQ 32323
> _______________________________________________
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