ARRL Satellite Bulletin ARLS029 (1997)

ARLS029 Mir ham operations to shift temporarily to 70 cm

Space Bulletin 029  ARLS029
From ARRL Headquarters
Newington, CT  September 5, 1997
To all radio amateurs

ARLS029 Mir ham operations to shift temporarily to 70 cm

Starting on or about Saturday, September 6, and continuing no later
than September 29, ham radio voice and packet operations aboard the
Russian Mir spacecraft will shift from 2 meters to 70 cm. An
''experimental'' worldwide FM simplex frequency of 437.650 MHz will
temporarily replace the current 2-meter operating frequencies.
Operations will return to 2 meters after the experiment ends. In the
meantime, the shift could make it a bit more difficult to work Mir.
For starters, power requirements will be higher than on 2 meters--25
W ERP or greater--although contacts using an H-T are not out of the
question. Also, some transceivers do not cover the satellite subband
(435 to 438 MHz).

The Mir International Amateur Radio EXperiment (MIREX) is conducting
the 70 cm test based on suggestions from several Amateur Radio
satellite groups who are interested in the feasibility of operating
Mir and the International Space Station on 70 cm. MIREX hopes the
experiment will determine whether the 70-cm frequency receives
interference from the existing commercial VHF equipment on Mir and
whether 70-cm operation will interfere with onboard equipment.

More important for simple ground stations, however, is whether
they'll be able to compensate for 70-cm Doppler shift on voice or
packet. MIREX President Dave Larsen, N6CO, concedes that Doppler
will be the biggest challenge for earthbound hams trying to work Mir
on 70 cm. The Doppler on 70 cm is plus or minus 10 kHz. Most radios
include 5-kHz tuning steps, and to work Mir on voice you will need
to get within 3 kHz of the Mir receiver frequency. To work Mir on
packet, the frequency error must be less than 2 kHz.

Miles Mann, WF1F, of MIREX reports he talked to Mike Foale, KB5UAC,
aboard Mir on 70 cm on Thursday, September 4. Mann was mobile at the
time, running 35 W. He reports very good signal quality during the
10-minute pass, which was at close to 60 degrees. Mann said he
compensated for Doppler by programming odd-split channels in
advance.  He reminds users that both the transmit and receive
frequencies must change, if you program channels in advance.

Larsen said this week that if the experiment does not work out, ''it
will be cut short.'' He said he hopes a filter that could be sent to
Mir as early as October will minimize desensing of the 2-meter
transceiver by Mir's  commercial equipment on 143 MHz.

To comment on the experiment or for more information, contact Dave
Larsen, N6CO, doc(at) or Miles Mann, WF1F,