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Mir SSTV Freq plan, Dec 14, 1998






SSTV Frequency options:
by Miles Mann WF1F,  MAREX-NA
December 15, 1998

Mir currently has three dual-band antennas dedicated for Amateur radio
access.  One antenna is located in the Mir-core module and supports
2-meters and 70 cm.  The next two antennas are located in the Proidia
module. Both of these antennas are the same type of dual band antenna,
2-meters and 70 cm.  One antenna is connected to the Safex 70 cm
transmitter and the other is connected to the SAFEX 70 cm receiver.  The
receiver antenna is also connected to a Diplexor 2-meter filter, built into
the SAFEX repeater.  This connection allows easy access to the two meter
portion of  that antenna.  This port is currently being used as the back up
antenna
for the Mir PMS (December 97 - December 98).

Option #1 70 cm
Assumes the following configuration:
A.   The Icom SAFEX II repeater is in normal operation (437.925, 437.950 FM
Split)
B.   The Kenwood PMS is in normal operation (145.985 FM Simplex)
C.   SSTV configured for frequency 435.975.
(options 2 & 3 were rejected)

The SSTV system will need to be connected to the Dual band antenna in the
Mir-Core, via
the existing Diplexor filter.  This configuration will support both the
2-meter PMS and the
SSTV system without any restrictions.
We do not want generate interference to the SAFEX II repeater system.  The
frequencies
chosen will keep the SSTV transmitter far enough away from the SAFEX
receiver frequency on
435.750 to avoid any interference.  The Cavity filters built into the SAFEX
will prevent the SSTV down
link channel from de-sesceing the repeaters input frequency.  The SSTV down
link channels is not currently used by any active amateur radio satellite.
Stations monitoring the SSTV signals will need to compensate for
the +/- 10 k Doppler swing.  Terrestrial test have shown that frequency
errors of less than 6k can offer good pictures (with a strong down link
signal).
Limitation:  None

The PMS will generate a third harmonic which would  cause a potential
problem while the Mir crew is
receiving a weak SSTV signal on 437.975. MAREX-NA anticipated this problem
and contracted to
have DCI build a special filter for the Russian Space Station Mir.  The
SAREX team helped test
and document the filter before it was delivered to Mir in September 1997.
The PMS signal is being passed through two different pass band filters.
The  PMS 2-meter signals first pass through a custom made DCI Cavity Pass
band filter, with a Notch filter on
143.625.  The Pass band will potion will pass all signals between 144.000 -
146.000 with less than 0.5 dB
of attenuation.  At higher frequencies the attenuation is greater than 40
dB.  The PMS harmonic of 437.955
will be attenuated by over 40 dB.
Then the 2-meter PMS signal will go into a Diplexer.  The Diplexer will mix
signals from the PMS on
two meters with signals from the SSTV on 437.975.  The Diplexer will also
help attenuate the PMS
harmonic.  It all works good on paper.  Even if their is a harmonic
problem, it will not bother normal operations.  The SSTV system will be in
automatic Transmit mode 99% of the time.  During the SSTV Uplink days
the Mir crew will be Talking on two meters voice and the PMS will be off
while the crew is talking.
Thus you should not have a harmonic problem.

Picking a good frequency is very challenging.  I spent weeks studying all
of the radio equipment on Mir and
band plans world wide to generate a list of possible channels.  The QRM
problems are actual very easy to avoid.
The Politics associated with frequency choices is what makes satellite
frequency selection
the most unpleasant aspect of this hobby.








Copyright 1998 Miles Mann, All Rights Reserved.  This document may be
freely distributed via the following means - Email (including listservers),
Usenet, and WorldWideWeb.  It may not be reproduced for profit including,
but not limited to, CD ROMs, books, and/or other commercial outlets without
prior written consent from the author.





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