A thirty-year-old piece of iron works perfectly! AO-7

Project director J.King W3GEY during AO-7 testsAMSAT OSCAR 7, AO-7, was released on November 15 1974. Although it was considered dysfunctional for several years, less than three years ago it was found, that it is operational.

The transponder depends on the energy supplied by the solar panels. During the day it is mostly in fashion B, but one – two flights (mostly in the morning) is in fashion.
For operation in mode B (uplink 432,125 – 175 MHz CW/LSB) a low-power transmitter or transverter is sufficient (approx.1 – 5W). Antennas with circular polarization are particularly suitable, but it is not a condition. The signal itself should be so strong, so as not to overload the transponder. Recognize this by distorting the downlink signal.

The downlink (145, 975 – 925 MHz CW / USB - pay attention to signal inversion) it is necessary to have a gain directional antenna (approx. 10 dB). The preamplifier will help a lot, because without it the signals are only S1 - 5, resulting in, that many stations add power to 70cm.

That the AO-7 is in mode B can be recognized by the beacon signal at 145,972 MHz. If he's not there, the transponder is in mode A or is switched off.

Without it, to be able to hear your own signal back works very hard. With SSB and CW signals, the Doppler effect is much more pronounced than with LEO FM satellites.

Mode A (uplink na 145,850 – 950 MHz CW/USB) is less demanding in this respect. As a minimum, QRP will suffice for a gain antenna (approx. 12 dB), but most stations prefer smaller antennas phased for circular polarization. The advantage of such antennas is, that it is not necessary to target so precisely (or not at all). Probably no station has 10m antennas with circular polarization, and so as to at least partially eliminate fading (signal leakage due to satellite rotation), they use circular polarization antennas at least on the uplink.

About 100W ERP is needed for solid operation, which can be achieved in different ways. For example, Stephen SO5AS, with which I worked uses uplink crossed dipoles powered by 120W. However, smaller yagi antennas are more common (4 – 7 the.) and performance adapted to them.

And downlinku (29,400 – 500 MHz CW/USB) are signals from S1 to S5. With signals, produced by RS-12/13 cannot be compared, but you can work. You need an RX (TRX) at 10m and antenna. The variability is great here, wire antennas are used, verticals but also turn signals.

It can be determined that the satellite is in mode A., a woman 29,502 MHz (+/- Doppler) working lighthouse. However, you will probably find mode A faster accordingly, that you can't hear at the 2m lighthouse (is not mode B) and stations appear around the middle frequency on the downlink.

From interesting sites, which I would recommend to those interested in operating through AO-7 are: Amsat Oscar 7 (AO-7),
Satellite antenna with circular polarization, Like on satellites?

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