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ARRL Satellite Bulletin ARLS012 (2001)

ARLS012 AO-40 Transponders Back on the Air!

QST de W1AW  
Space Bulletin 012  ARLS012
From ARRL Headquarters  
Newington, CT  July 20, 2001
To all radio amateurs

ARLS012 AO-40 Transponders Back on the Air!

AO-40's transponders are back on the air, following an orbital shift
that put the Amateur Radio satellite into an orbit that AMSAT says
should be good for many years to come. Transponders have 435 MHz and
1.2 GHz uplinks and a downlink in the 2.4 GHz ''S band.''

The transponders have been off since late May, when preparations
began to shift AO-40's orbit at perigee. That operation was
completed earlier this month, and ground controllers have been
readjusting the spacecraft's attitude since then.

Ground controller Stacey Mills, W4SM, said the transponders would
operate from orbital positions MA 10 through MA 99. Uplink
frequencies (without taking Doppler into account) are
435.495-435.780 MHz and 1269.211-1269.496 MHz, and the downlink
passband is 2401.210-2401.495 MHz. The transponders are inverting,
so a downward change in uplink frequency results in an upward
frequency shift in the downlink.

Mills emphasized that earthbound ops should not use any more uplink
power than necessary. He also noted that the transponders could be
switched off to accommodate additional testing.

AMSAT Awards Manager Bruce Paige, KK5DO, in Houston, was among the
first stations to get on AO-40 after the transponders were
reactivated. ''It sounds awesome,'' Paige said. ''I am transmitting
with 25 watts up, and it sounds great!'' In addition to some domestic
contacts, he and his daughter, Mahana, W5BTS, worked EA8/DJ9PC in
the Canary Islands.

Although AO-40's attitude still is not optimal at this point, ground
controllers had to suspend operations to adjust it after an onboard
sensor lost its view of the sun. Without data from the sun sensor,
ground controllers cannot be certain of the satellite's attitude.

Mills said now that the ground team has ''a very good fix'' on the
spacecraft, they'll do nothing to change its attitude for several
weeks, while the solar angle decreases. Once the sensor regains its
view of the sun, efforts to adjust the spacecraft's attitude will
resume, so that AO-40's antennas are pointing toward Earth.

Mills said ground controllers will use the interim period to see if
they can re-calculate the so-called ''mystery effect'' that had been
impacting AO-40 at perigee under its former orbit.


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