ARRL

ARRL Satellite Bulletin ARLS019 (1997)

SB SPACE @ ARL $ARLS019
ARLS019 Mir frequency test

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Space Bulletin 019  ARLS019
From ARRL Headquarters
Newington, CT  June 19, 1997
To all radio amateurs

SB SPACE ARL ARLS019
ARLS019 Mir frequency test

For the third time in less than a year, the Mir FM voice and packet
frequency changed again June 15. But even as it was made, the switch
to 145.985 MHz simplex was being called ''tentative'' and
''experimental.'' It also was controversial. As a result, Mir
officially will end the worldwide ''experiment'' on 145.985 MHz as
of June 23, but leave the frequency available as an option to the
Mir crew only while Mir is over the US. Mir packet sysop Miles Mann,
WF1F, said US astronaut Mike Foale, KB5UAC, now aboard Mir, can use
''any channel he wants'' when he's over the US, including 145.985,
but he has to switch to 145.200/800 when Mir is elsewhere. Also, the
radio will remain on the split pair when the crew is sleeping. The
new frequency may be used for both voice and packet operation.

The Mir International Amateur Radio Experiment--MIREX--cited
''numerous complaints from around the world'' that the 145.200/800
split-frequency combination did not work very well as the main
reason for trying 145.985. Last November, Mir changed from 145.550
MHz simplex to the split-frequency pair. ''The radio has been almost
impossible to use since November 1,'' said Mann, who called 145.985
MHz ''an excellent compromise.''

In a posting to the AMSAT bulletin board, John O'Hara, KB8TJX, in
Wellsville, Ohio, reports he worked KB5UAC aboard Mir on 145.985 MHz
for several minutes right after the changeover. ''Mike said that it
was working out a lot better for him also. He said he had trouble
sorting out the voice contacts from the packet and that the duplex
was also confusing to him,'' said O'Hara, who's AMSAT coordinator
for Eastern Ohio, Western Pennsylvania and the northern panhandle of
West Virginia.

When the ''experiment'' was announced, Mann had expressed the hope
that if the 145.985 MHz channel worked much better, the Mir crew
might be more inclined to get on the air than previously. Mann said
the 145.800/200 MHz split-frequency operation suffered from
interference from terrestrial users and drew widespread complaints
from hams in the US, Japan and Australia (145.200 MHz is a repeater
output or input frequency in many countries). He said the new
frequency complies with the IARU band plan for satellite operation
and will reduce desensing of Mir's 2-meter station by commercial VHF
activities taking place aboard spacecraft in the 143-MHz range. Mann
said MIREX is working on a fix for the desensing problem, and hopes
to have it in operation by this fall.

A return to the 145.55 MHz frequency used previously by Mir was
rejected because it's too close to a popular simplex frequency in
Europe. Switching to 145.79 MHz also was out because it's in use by
many semi-permanent packet operations.

Equipment aboard Mir includes a Kenwood TM-733, a PacComm
Handi-Packet modem, a dual-band antenna, and a new, huskier power
supply capable of powering the TM-733 to its full 50 W output. Mann
said the output power typically is 10 W, however.

MIREX requests reports on the 145.985 MHz channel. Signal and
interference reports go to Dave Larsen, N6CO, Box 1501, Pine Grove,
CA 95665; e-mail doc@volcano.net.
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