The Effect of LNBs Modification on Their Noise Properties

  • Since my OM6AA station is currently QRT due to TRSV failure, I worked out small paper with LNBs measurement. See attachment. I guess, that experimenters with small downlink antennas can find some usefull information in this paper.


    73 & GL

    Rasto A75GR/OM6AA

  • Interesting. Keep it up.


    There are no signals at the image frequency. Things would be a lot worse if there were. One should be able to estimate G/T with a known amplitude signal compared to the noise floor where there are no signals. I only see a 10 dB lift between the NB transponder noise floor and adjacent noise. It ought to be more but my system is not optimised. If I knew the power density of the transponder noise floor I could work out my G/T. This can be done for all antennas that can make this measurement. One can also do this with a beacon of known power but none of the QO100 beacons have constant amplitude which makes things difficult. Perhaps Bochum can tell us what the transponder noise floor power actually is?


    Mike

  • Hi Mike,


    you can use Sun8) to cold sky measurement to get G/T of your Rx system. It is common technique from radio astronomy. It is also used often to measure EME setup. Then you can apply VK3UM EME calculator to get final data. However, when your transponder noise floor is 10 dB, you must have good Rx system with sufficient signal margin to cover a possible link deterioration (heavy rain, snow etc.):)


    73 & GL

    Rasto

  • Hi Mike,


    I find it interesting that you mention QSB on the QO-100 beacon signals - and I have heard that commented before. Can you specify how much QSB you see? Like many others I also use the beacon signals for checking my setup, making ajustments, improvements etc., But I find the signals quite stable with variations less that half a decibel or so. (I have ofcourse seen greater variatinon during very heavy rain, but that is not something that happends often)


    Maybe we could find a time on the satellite to exchange observations?


    73 Ole OZ2OE

  • If you have ever handled a 2.4m solid Andrew dish, which I expect you have, you will know that pointing it at things is not something to be taken lightly. Heavy and unwieldy doesn't really describe it adequately. So, I have not done the cold sky measurement. I have acquired an azimuth bearing that once I can get mechanical assistance to install I will be able to do this. That will be interesting I think.


    Mike