OSCAR AO-40 from 3B9C

Overview of the proposed OSCAR 40 operation.
by David, G0MRF

Satellite Status
Oscar 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.

Satellite Orbit
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 safety permitting).

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 feature.