Re: [amsat-bb] Mir bounce

[Roy Welch <rdwelch@xxxxxxxxxx>]

Hi Jean-Louis,

I have noticed that sometimes when I track MIR in FM mode that my squelch
opens even though MIR is not transmitting.  When this was happening, I
moved my beam left and right from the MIR position and the squelch closed
again.  It only opened when I was pointed at MIR and this "open" condition
followed MIR across the sky.  This happening was also noticed by Junior De
Castro in Brazil.  There was no communications heard, just a barely open
squelch with noise.  

I believe this was caused by the squelch circuits in the FM receiver
detecting a threshold quietning of the receiver because of the hundreds of
earth stations calling MIR for a QSO.  The external antenna on MIR may have
been excited by all the rf from the ground and reradiating a small portion
of it back again.  This same condition has been used by some to receive TV
signals behind a mountain range by putting back to back tv antennas on the
mountain top and pointing the receiver antenna at them.  At any rate, what
ever is causing it, I believe there is some reradiation of ground station
RF.  I think it would take a pretty good TX/RX setup to be able to
establish even one way communications.  Perhaps CW would be worth a try
with a moon bounce class station.

Jean-Louis.RAULT@tcc.thomson-csf.com wrote:
> 
> > > All of the Amateur Radio equipment on Mir is currently disconnected,
> > > however, have you tried to bounce your signal off of Mir?
> > > It called Earth-Mir-Earth?
> 
> Last summer, I organized a Mir bounce experiment.
> The team was composed of about 10 skilled french hams and we performed many
> skeds.
> We were using AO-10 class equipment working on 145 MHz, that is 50 to 80 W
> RF output to 10 or 12 el yagi beams.
> Preliminary link budgets were showing that a little positive S/N ratio could
> be obtained (with narrow band CW) if the equivalent surface or MIR was 100
> square meters or more on the 2 meters band.
> My own reception chain was including a 11 el circularly polarized yagi beam,
> followed by a SSB Electronic AsGa preamplifier and an ICOM IC-821H
> transceiver. That equipment allows me to clearly hear some Moon bounce
> stations.
> I used FFT tools like Spectrogram and CoolEdit 2000 as an help to detect
> tiny sigs in background noise.
> I must admit that we NEVER get any positive results (yes, we took the double
> Doppler effect into account).
> This pessimistic test report is just to inform any future MIR bounce
> candidate about the minimum rig performance he has to deal with.
> 
> We plan to start a new campain in the next few months, with more RF power
> and larger aerials.
> We hope to be ready before MIR lands  ...
> 
> Cheers
> 
> Jean-Louis F6AGR
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-- 
73, Roy

Internet: w0sl@amsat.org
Home Page: http://home.swbell.net/rdwelch
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