Hi all: I agree with Bobs 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 Andys right wrist. Its 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 [email protected] 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
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