OSCAR AO-40 from 3B9C
Overview of the proposed
OSCAR 40 operation.
by David, G0MRF
40 is operational with 2 transponders. 435MHz uplink to 2.4GHz down or
1269MHz uplink to 2.4GHz.
The orbit of AO-40 passes through two eclipse periods per year. During these
periods the transponder ‘on’ time is severely reduced. The eclipse periods
last approx 2 months. March and April next year will not fall in an eclipse
period and full transponder operation can be expected.
Oscar 40’s orbit is almost equatorial. i.e. the satellite appears to be
above the equator. In practice this means that for stations in the Northern
hemisphere the satellite will always appear in the southern sky and for 3B9C
the satellite will appear to pass from East / NE / N /NW finally crossing
the westerly horizon. It will never appear to the south of 3B9.
The satellite is available up to 14 hours per day and is available on 3 days
in any 4 day period.
The image below is taken from the tracking program Nova. The area covered is
the satellite ‘footprint’ and is shown hatched. Any stations within the
hatched area can communicate with each other. In this example 3B9 has all of
Africa Europe and a large portion of North and South America within its
range. There is one limitation on coverage; no single satellite can provide
coverage to a point on the opposite side of the Earth’s surface.
Unfortunately for us, this area will include California.
Equipment and site
The station needs to generate CW / SSB on 435 MHz at about 1kW ERP. To
receive signals from AO-40 on 2.4GHz, a small 0.6m dish antenna is used. The
dish is fitted with a down converter which converts the 2.4GHz signal to an
output on 29MHz. From your position in ‘the shack’ the radio/s will be set
to transmit on 435 and receive on 29MHz. Operation is full duplex, so you
can hear both sides of the QSO.
The site for the AO-40 station should give unobstructed views in the
direction of the satellite. At 2.4GHz an inconveniently located palm tree
will render the signal unusable.
To track the satellite, azimuth and elevation rotators are desirable.
However, height is only needed to overcome local obstructions. If situated
on a northern shoreline with an open view to the sea, it is entirely
practical to put the antennas on a small 2m high mast. (Site security and
To avoid excessive losses in the coax feeders, the 2.4 GHz converter is
always mounted at the dish antenna. On 70cms, RG213 coax should be limited
to about 10m. If the run required is longer, then it is normal practice to
have any 70cm power amplifier mounted near the antenna.
The proposed equipment list includes a 7 W input 100W output amplifier and a
19 ele yagi for 70cms. This will give a margin of between 3 and 4dB on the
normal uplink requirements.
Read our special how to work us via AO-40
Behind the Scenes
Written by the team that brought you 9M0C,
D68C and the forthcoming visit to 3B9C