interferences on datv transponder

  • Hello everyone.

    Recently, interference probably caused by radar signals has been occurring with increasing frequency. this can also be seen from very fast signal drops on the wide band transponder. I verified during yesterday's datv net Italy that the interruptions corresponded to the flashes I saw on the batc waterfall and also on my hdsdr spectrum. these signals cause the agc to intervene and consequently interrupt the data flow with the result of loss of video and audio reception for a few seconds on the minitiouner. These are my observations. Since it is a problem that affects all users of the transponder, it would be interesting to analyze the problem and eventually find solutions.

    I enclose some screen shots.

  • Hello Raffaele, yes i confirm i have also noticed the problem.

    A few months ago the problem was less frequent, but now it often occurs.

    The signals are all lowered at the same time, seeing the QO-100 specifications (…resentations/Eshail-2.pdf) of the WB transponder there is no AGC unlike the NB one, the errors increase and the receiver loses synchronism in the instant that probably corresponds to the disturbance due to packet corruption.

    It is known that the S band is used by meteorological radars ..

    I noticed that using symbol rates lower than 333k the phenomenon is less marked probably because the receiver buffer empties less quickly and is less noticeable even if the problem is always present.

    A small adjustment can be made by sending the keyframe faster for example 1-2sec (OBS streaming mode) or FPS value x1 or x2 (OBS recording mode) in order to keep the receiver more hooked even during freezes.

    Even the use of FEC 3/5, 1/2, 2/5 could limit the problem in RX, even if you have to reduce the video bit rate; by inserting more redundancy bits the receiver could better reconstruct the missing or damaged data and limit the problem.

    If you look at the BATC spectrum by selecting the FAST speed in the options you will notice a drop in the signals in random mode, you can see it well on the beacon signal that suddenly drops by 1-2dB and in that moment also on the beacon signal you see the interruption.

    Sometimes it happens even several times in 1 minute and sometimes it is necessary to wait a few minutes to see the phenomenon; in the evening the problem is more pronounced

    Roberto IS0GRB