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Messages - Georg

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Timing / Re: Pulse collision avoidance
« on: June 13, 2018, 11:34:54 AM »
Hello Daniel,

sorry for the late reply - I just saw your questions now ....

In Graz, we have tried to optimize this overlap avoidance procedures / minimize the rep rate losses, using the FPGA on our home-made PC card:

- This PC card creates the laser firing pulses, and triggers the HiQ laser
- The FPGA stores all future return event times of just fired laser pulses (sseveral 100 events for up to GEO satellites) in a FIFO
- On each laser start pulse event, the FPGA checks the time difference between this laser firing epoch, and the next return epoch time
- If the next return epoch time is closer than 100 µs (can be adjusted...), one additional 100 µs delay is inserted before the next laser fire command,
  followed then again with laser firing commands in the usual 500 µs intervals (then referred to this first delayed one)
- When the echo of this first delayed pulse arrives, and the overlap conditions is still alive, once again a 100 µs delay is inserted .... etc....
   as long as the overlap conditions is valid
- This procedure reduces the rep rate only during overlap, and only by a very small percentage (e.g. from 2 kHz to 1960 kHz or so; depends on satellite)

This overlap avoidance procedure can be enabled / disabled by setting a control bit via PC.

Works perfect for 2 kHz (and a bit higher); for > 10 kHz, the 50% operation might be necessary, but this is a rather high price ... it might be better to just neglect overlaps, which could be acceptable in view of much lower energy per pulse (i.e. less backscatter).


Ideas / Making satellites visible during daylight ranging
« on: May 06, 2016, 11:16:32 AM »
Hi everybody from Graz !

During our last visit at Potsdam SLR station in March 2016, Lutz Grunwaldt showed us CCD images of short visible flashes of Envisat during a daylight tracking session - a surprise for us !

We have now installed a proper CCD in our detection package, and have started to visualize at least large targets during daylight tracking; we expect it to be quite useful when tracking e.g. debris using TLE with larger TB values etc....

We have started now to fill a list, which targets we have seen already during daylight... maybe I can report more about, when I am back from a 3 week holiday, which will start tomorrow :-)

Any other experiences with that ?


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