Expected SN with a 80cm dish on NB transponder

  • Of course I know the Amsat recommendations. The purpose of my comment was to encourage new users not to be frightened by thinking large antennas are needed. Certainly not for the transponder NB.

  • Of course I know the Amsat recommendations. The purpose of my comment was to encourage new users not to be frightened by thinking large antennas are needed. Certainly not for the transponder NB.

    Hello Lucio


    A common 85cm TV satellite dish is not large and can be mounted on a tripod. See my QRZ.COM site. 40cm are too small for the dish I think. I encourage also new users ;)


    73 and stay save and healthy

  • Hello Nicolas,


    How long is the cable between the LNB and what type of cable is it? Is there anything else in that path - a DC power inserter? Or are you peaking the antenna by looking at the NB beacon using a laptop very close to the antenna?


    73 Chris G4SDG



  • This is with the same dish as Goonhilly uses (~1.2m), lower beacon is blue 40dB - 6dB of noise floor (red) = ca, 34dB difference:


    I know that I could improve ca. 1 dB of sensitivity from my WB measurements. Investigations to be done soon.

  • I've tried azimuth, elevation, skew, several times, it seems to me that it's the best I can get…

    How wide was your AZ/EL search pattern? Some OMs optimize on a sidelobe of their antenna. With non-optimal feeds, these sidelobes can be sometimes misleading.

  • My money would be on non-optimal alignment.

    How about the dish quality and or its feed mount position accuracy, if everything else has been tried already?


    I am getting 3dB noise floor hump on a 75CM dish - that matches quite well other "well receiving" setups reported here.

  • " I am feeding the LNB with 13V, supposed to be vertical polarisation…


    Anyway, I'll keep searching how I can improve this…"


    Please beware:

    Feeding the LNB with +13V does not ensure vertical polarisation alone.

    If you feed +13V but mechanically rotate 90 Degrees you still get horizontal polarization !!


    Personally i first stumbeled about DC-feed problems cause my homebrew bias-T

    had not enought bandwith and was blocking everything above 500MHz - check your IF path aswell


    73 Marcus

  • I am feeding the LNB with 13V, supposed to be vertical polarisation…

    ... the 13V is the one point of power source, the available current another error source. Where do the 13V come from? Is there enough drain available for the LNB? Are there any DC resistors on the coacial cable? Are the 13V also on the LNB available?

  • This looks all good. Is Power Supply 12V or 13V?

    An other question: sight is free to the satellite, no roof, no wall, no tree or anything else in the direction to the sat?

  • EA4GQY Hi Nicolas,

    Thanks for posting the pictures. Your situation for adjusting the dish and/or LNB clearly is not very easy!.


    I am just thinking about another HAM having receive problems some time ago, but was using his dish with the (adjustable) LNB-arm not in the correct position = fully downward. Did you check this on your dish, otherwise the LNB will be not in the focal point....


    73 and stay safe!

    Ed

  • Hi again Nicolas,


    Looking closely at your picture it seems that your LNB skew-angle is not correct!. It should be about -30 degr for Madrid and I estimate that your LNB skew is close to 0 degrees?. When you compare with my LNB set to abt.-15 degrees than yours would have to be turned a bit more into the same direction. This would explain the small signals....!


    73 Ed

  • Thank you Ed!

    The LNB arm is fixed with some kind of plastic, but you are right, I am going to try to remove this plastic thing and move the arm up/down and see if I can get any signal improvement, I'll give another try to the LNB skew too…

    I'll keep you informed, thank you for your help!!

    Stay safe!

    73, Nicolas