DATV Beacon A71A C/N and signal strength decreased?

1st Official Post

    A71A DATV beacon has 0.8dB lower MER (alone) compared to 5.July.2019/3.Aug.2019. Did they change uplink power or is my system degraded somehow? I got never the good MER of 8.8dB since 3.Aug. even at clear sky and empty transponder.


    I would like to know this for comparing my receiving situation with different LNBs and more...

    Hi everybody

    I've just read this thread, and with my 60cm dish I've managed to achieve MER 5.5/5.6, but today it has reached 5.9/6.0.
    Hardware is MiniTiouner-Express
    60cm offset dish
    LNB Octagon Green

    Salomão Fresco

    Callsign: CT2IRJ

    GRID Locator: IM59re -- CQ Zone 14 / ITU Zone 37

    QTH: Fazendas de Almeirim, Portugal

    It is about 10.3 dB this morning but I have noticed it falling as low an 9.8dB in the daytime, lower if there are other strong signals.




    The beacon is a bit too wide for my liking and reducing it to 1 MS or less would help with the over-crowding we are now seeing on occasion. Some stations like to transmit 1 MS and we can only accommodate two of these with the current beacon. Only one 2 Ms signal is possible and nothing wider. We all had fun with experimenting wider signals when the beacon was off. Perhaps even 500ks but H265 would be a good compromise.


    Meanwhile, several of us have been experimenting with lower bandwidths and higher order modulation. 66ks is 33ks are very usable and can be done with low power.


    Mike

    OK Mike, I've tested the "good C/N MER values" in the morning. I'll try this again. What kind of dish do you use? I guess you're using a POTY feed. Would be interesting to know of which parts your receiving system consists.


    Sometimes I think my C/N correlates somehow to the signal seen on BATC WB monitor...


    Regards Mike

    My dish is 2.4m and the LNB is a properly modified Octagon Quad, though the MER is often better with unmodified LNBs. It is important to observe the impact of the reference phase noise and select a LO that minimises this. If using a Leo-Bodnar like I am, a change of 1 Hz can make a difference. Aim for minimum phase noise and maximum stability, not absolute accuracy as you can always correct for the latter.


    For DATV use, there is no need to modify the LNB LO. However, I also use SSB where it is necessary to for the LO to be much more stable.


    Mike

    Interesting Mike. I'm using Leo's GPSDO because I'm on the NB transponder in SSB as well. The LNB was wobbling terribly.

    After realigning my dish the MER is at the same level as it was at first install without having the LNB modified.

    I'm using the recommended setting from Leo Bodnar for 27 MHz & 10 MHz. If you have better recomodations to set up my GPSDO please let me know.


    BTW: is a MER of 10dB the maximum possible value? I think there is a limit.


    73 Mike

    I think his settings will be optimum, my LNB required 25 MHz but I am not running less to have an LO of 9.5 GHz when puts all signals 250MHz higher and DATV signals into the range the Octagon SF8008 can receive them.


    I think the maximum was 11.7 dB with the 30m dish at Goonhilly.


    Mike

    You can be happy yes. I get at best 10.6 dB. This morning, with heavy cloud and no other users, it had dropped to 10.2 dB.


    When developing I noted that the phase noise is really important. For example, on the BBC transponder on BADR with an unmodified LNB I got an MER of 13 dB with a 1.2m dish. With a GPS locked LNB it was very much worse. This is a much wider bandwidth. It depends on each LNB and the phase noise of your reference. With that MER, I think you are OK.


    Mike

    since a few days I have problems with the beacon too.

    Received it for two month without any problem, but now it looks like that:



    any idea what the problem could be ?


    I can receive all other signals in good quality, just the beacon makes problems.


    vy 73, Kurt, DJ0ABR