FILTER for Downlink is needed (if you use an sdr for receive)

1st Official Post

    Nearly all sdr have a problem that they also receive the 3 times and 5 times (and above) frequency

    means if you have your rx tuned to 740 megs (rounded up a bit) ... it also receives on 2.22 gig


    since a few days a new tv transponder on the sat was switched on on 11.970 ...

    minus 9.75 equals 2.220 ... voila we have noise on 740 megs :(


    several ways to solve it


    you can add a narrow 740 megs filter in your setup (there are saw filters available for that range)

    you can add an "lte-filter" in the lnb cable (a 800 megs lowpass filter with dc feed trough)

    you can add a 2.2 gig notch inside your bias t (just an inch of coax need as an open end stub)


    i now have two of the above solutions combined (the lte filter PLUS the notch for 2.2 gig in bias t)


    normally one of the three solutions should be enough but i got the lte filter after i added the notch so i left it in


    spectrum now is super clear again


    greetz dg9bfc sigi

    The problem was also discussed on Twitter. I think that the new transponder is not the cause of these interferences but the proximity of an LTE BTS in your vicinity. Note that not everyone has these interferences and this should be a clear indication. Some LNBs already have an LTE filter, others obviously don't have this filter. With a LTE filter of a few euros placed between the output of the LNB and the SDR dongle solves the problem.


    P.S.

    I use an Octagon Twin OTLSO without any interference problem

    No filters added, no problems.

    IT IS THE NEW TRANSPONDER ... tune sdr console to 11.970 and see the stripes


    (if you have a different lnb frequency is a different story!)


    in some setups 2 gig is a few db lower and noise can not be seen (or just barely) depending on how your setup is done ... length of cables... bias t used etc etc

    many things influence the losses on 2 gig while on 740 megs all the attenuation factors are a lot lower ... and that is the reason why some do see those streipes and some do not ...


    the stripes are NOT from lte (even if an lte filter helps in this case)

    Quote from DB2OS

    To be clear, this "new transponder" is on ASTRA at 28,8°E and not from Eshail2.


    If your antenna is not optimal pointing to 25,5E or has a wide beam (small dish), it may have some influence..

    Nothing has been seen from the new transponder here… I’m the lucky one or the 1.1 dish reject any interference from the astra bird.

    Quote from DB2OS

    To be clear, this "new transponder" is on ASTRA at 28,8°E and not from Eshail2.


    If your antenna is not optimal pointing to 25,5E or has a wide beam (small dish), it may have some influence..


    I have an SDR and unmodified PLL-LNB, fortunately not a glimpse of the stripes you are seeing.

    In fact, any transponder on Eshail2 could never cause interference in Northern Europe since ALL Eshail transponders transmit on a mena beam. I receive with 100 cm Dish, unmodified Octagon Twin LNB OL 9750, RTL-SDR V3

    No interference before or after switching on this phantom transponder.

    On the frequency of 11976 V (Badr 4 @ 26 ° E) I receive this transponder without any interference on NB QO-100.

    Even though you may not see any interference, it's worth trying a filter in front of an SDR as you never know if there is degradation until you try it. While this interference is producing lines, other interference may appear as a rise in the noise floor. As the NB transponder is very strong and with a 1m dish you see it's noise floor there might be interference below the noise so it won't matter much but on wideband it might be impacting the signal to noise ratio a bit more. For €6 it's a worthwhile investment.