Question on QO100 design

  • Something I'm just wondering..

    The narrow-band transponder uses RHCP on uplink and vertical polarisation on downlink.

    The wide-band transponder also uses RHCP on uplink but uses horizontal polarisation on downlink.

    Why is the downlink polarisation different?

    Why is the uplink polarisation the same?

    (I do see it's a lot easier to switch the polarisation of a LNB than of a circular antenna - still I wonder what the advantage is of different downlink polarisations?)

    Geert Jan

  • pe1hzg Jan, the reason is to give you a simple setup for both transponders. you can also receive the nb im you are listening the wb.. only 3db less signal.. nice weekend..Heiner..

    The isolation between H and V is more than 3dB - in fact, in broadcasting H and V polarisation are used to distribute different signals on the same frequency.

    If WB and NB would have used the same polarisation, one LNB would receive both at the same time. I'm now using dual LNB's for that reason. Not the end of the world but I wonder about the reason for this this this way on QO100.

  • A look at the block diagram sometimes says more than 1000 words ;-)

    There is ony one single S-Band Uplink antenna dedicated to us and RHCP was the best choice.

    NB and WB path are completely independed, separated after the antenna via redundant paths.

    There is also only one dedicated feed for our X-Band Downlink.

    Since any commercial LNB use H/V polarization, this was the perfect solution to connect both NB and WB to the same feed and same antenna. Like on the commercial Sat-TV downlinks, we could also use the same frequency or overlapping frequencies just with different polarization.

    We always propagated the use of Dual-LNB in case you want to receive both NB and DATV at the same time and it costs almost nothing...