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Fulltime Transponder Test – Amateur Mode

by on March 18, 2014

Update 29 Mar 19:56 UTC
FUNcube has now been commanded back into ‘auto eclipse mode’, ie it will be on low power beacon + transponder on when in eclipse, and full power beacon/no transponder when in sunlight

Update 29 Mar 10:29 UTC
FUNcube is now in permanent amateur mode (low power beacon, plus transponder on)

Update 25 Mar 15:00 UTC
Results of last weekends tests: the transponder was maintained ON for two orbits, and we did not see any noticeable fall in battery temperature. We are therefore proposing to repeat the test next Saturday (29 Mar), but leave the transponder on for a longer period. We will switch it on during the first pass over the UK (approx 10:30 UTC) and switch it off during one of the evening passes over UK, the first of which is at approx 20:00 UTC.

We are particularly interested to receive TLM when the satellite is coming out of eclipse (ie when it should be at its coldest temp). So reception from suitablely located stations would be very welcome.

If you hear the transponder on, please feel free to use it!

73s Jim G3WGM

Update 22 Mar 12:45 UTC
I have now switched the sat back to ‘auto eclipse’ mode (at 12:45 UTC), such that in sunlight the full power beacon will be on, and when the sat is in eclipse the transponder/low power beacon will be on.
Initial examination of the tlm makes me think that the battery temp didn’t drop appreciably more during the two orbits than when in auto eclipse mode. The management team will discuss this tomorrow, and decide what the next step is!
73s Jim G3WGM

Update 22 Mar 09:29
Just to let you know that at 09:29 UTC today I have switched AO-73’s mode to be continuous transponder/low power beacon. The plan is to leave it in this mode for one or two complete orbits.
Anyone decoding the tlm, please keep a watch on the Battery Temp – its important that it stays above -5 degs.
Please feel free to use the transponder while we are in this mode.
73s Jim G3WGM

On 22 Mar, we will be commanding the satellite into transponder mode for one or two orbits so we can assess the effect of lower power being radiated by the sat on the battery temperature. We expect the sat to be put into full time transponder mode (aka amateur mode) during the first morning pass on Sat 22 Mar over the UK, ie at approximately 0930 UTC.

We are aware that the on/off timings for the transponder are not now ideal, due to seasonal changes. In the coming months the situation will get worse such that in June the transponder will only be available for very short periods in the Northern Hemisphere.

We are therefore planning to alter the schedule such that the transponder is on continuously at weekends, ie after approx 1900 UTC on Fridays, to Sunday evening. This will give radio amateurs a greater opportunity to use the transponder. Unfortunately there is no way of automating this schedule, so its maintenance will rely on the availability of command stations.

Before implementing this schedule, it is necessary that we characterise the effect of maintaining transponder mode for long periods of time. We expect that the space craft will be slightly colder than when transmitting at full power, as the heat generated inside the spacecraft by the PA will be less.

We are concerned that this lowering of the temperature may bring the battery temp lower than is advisable. Its specification is that it should not be charged if its temperature is below -5 degs, or some damage might be done to the battery. Currently the minimum temperature we see that the battery reaches is approximately -2 degs.

If you notice that the transponder is open on 22 Mar, please feel free to use it.

Please note that we have learnt from experience that commanding the sat is not an exact science, and that not all commands sent are received by the satellite, probably due to interference. We will announce on AMSAT-BB and on the FUNcube web site ( the progress of our tests. We would be very grateful if as many listening stations as possible receive the TLM and forward it to the warehouse on Sat 22 Mar. Thank you.

73s Jim, G3WGM

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