[sarex] Future ISS amateur radio modes, de-sense

[MM]

Hi all:
I agree with Bob’s analysis on the same band up/down
links on ISS or similar space stations.  We had
similar interference problems with Mir and ISS already
with the ham gear.  The Russian space agency uses VHF
transmitter on 143.xxx MHZ as an emergency frequency. 
They test this frequency frequently to verify the
terrestrial ground stations can still hear ISS.
Occasionally they will just hit the TX button for a
few hours to make sure all of the ground stations are
listening (I have seen this on ISS too). The
transmitter power levels and Gains for the ISS
transmitter are not known.  However it is known that
when the 143 MHZ transmitter is running, the ham radio
listening on 2-meters will go deaf!  

I did some testing with the Mir Space station that was
using a Kenwood TM-733 transceiver to see how much
power was required on earth to punch thought the
de-sense while 143 MHZ was active, and it was a lot. 
In 1996 Astronaut Gerry Linenger was on frequency
calling me at AOS for a pre arranged phone patch to
his brother in Michigan (1500 miles distance to Mir
maximum).  We were using an uplink frequency between
145.825 – 145.900. The Russian crewmembers were
chatting away on 143 MHZ in voice (FM 10 kHz
deviation, power and antenna locations on Mir
unknown).  I was running 300+ watts of raw RF into 80
feet of RG-213 coax.  The antenna was an M2 with 22
elements circular polarized (12 dBd gain mimimum). 
Antenna positioning was computer controlled in Azimuth
and Elevation.  The ERP I was generating was more than
2400 watts.  The pass I had chosen for the Phone patch
was a very high pass, typically over 70 degrees, which
means that Mir would be passing less than 400 miles
from my QTH at its closest point.  Gerry kept calling
me, but he could not hear me until he was right over
my QTH.  We only had contact for a few seconds.  Then
as the pass by, the de-sense caused by the 143 MHZ
transmitter over came my 2400 watt ERP and contact
lost.

The frequency separation between the two radios was
over 2.2 MHZ.
The distance between the two antennas is not known
exactly, however ill guess it was between 10 feet and
not more than 50 feet.  Both antennas were most likely
mounted on the “Mir Module”.  On ISS we have a similar
issue and that is most of our antennas are mounted on
the “Service Module” which is the same place as the
143 MHZ transmitter.

After the De-sense test with Mir, the MAREX and SAREX
teams worked together to install a special 5 pound
custom filter build by DCI.  The filter had 4-tuned
cavities and a fifth cavity that included a special
notch filter for the exact 143 MHZ transmitter. In
February 1998 the Russians delivered the filter
http://www.marexmg.org/fileshtml/radiohardware.html
The DCI filter can be seen next to Andy’s right wrist.
 It’s the rectangle box with the white printed label.

The new filter allowed us to carry on School schedules
and other communications while the 143 MHZ transmitter
was active.  The reason this Mir DCI filter was
successful was because the 143 transmitter and the ham
145.985 receive frequency were over 2.2 MHZ apart. 
This is how we were able to get away with such a small
filter.  If were to try a similar multiple 2 meter
up/down projects on ISS, it could be done, however we
would need bigger and heavier filters because our
separation would be approximately 1.5 MHZ separation. 
We also have size limitations.  But if you know who to
talk to at NASA and have the $$, I am game.


WF1F Miles at MAREX



--- Robert Bruninga <bruninga at usna.edu> wrote:

> > The ISS is a sufficiently large mass of metal that
> 
> > tremendous same-band isolation should be
> achieveable 
> > by simply mounting antennas on opposite sides of
> the 
> > station,...[etc]
> 
> Unfortunately, Not really.  I am sure that if we had
> two
> magmounts and could crawl all over the outside of
> ISS with long
> enough cables, that two mutually isolated locations
> could be
> found (kind-of-a- can you hear me now? Kind of
> test).  But NASA
> does not allow us the resources for that kind of
> approach.
> 
> But even if you did find such a location, or even if
> you did
> spend a few millions of dollars doing an RF analysis
> of such an
> arrangement, it would all change when ever anything
> moved.  And
> things are always moving up there.
> 
> Also, not only does one not even attempt to plan
> weak signal
> same-band operations from the same Field Day site,
> one would
> never risk several years of planning and millions of
> dollars of
> effort on something that critical that might be
> desensed as soon
> as the solar arrays moved 10 degrees..
> 
> We had several amateurs do tests of several 2 meter
> radios to
> discover how much power on one 2m radio was needed
> to descense
> another 2m radio and the power level was down around
> 10
> milliwatts at 100 foot separation and it still
> caused 10 dB
> desense. (I think I remembered those right)...
> 
> Unfortunaly then, we simply cannot plan on up and
> downlinks in
> the same band while hoping for independent
> operations without
> constant crew intervention with every single mode
> change that
> affects that band.
> 
> Bob Bruninga
> 
> ----
> Sent via sarex at amsat.org. Opinions expressed are
> those of the author.
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