RX sig strength 7 db lower with POTY

  • Hey all,


    I mounted my RX-TX (Diavolo Twin LNB and POTY) combination in my 80cm offset dish today.




    The RX signal strength of the CW beacon with that RX-TX combination is about -84 db.


    The RX signal strength with just the RX LNB mounted is about -76db at the CW beacon. So there is a loss from about 6-7 db with the POTY mounted.


    Unfortunately mechanical wise I can not push the 10GHz feedhorn more further to the back due to the LNB mount.


    Is anybody having the same issue and how did you overcome that signal loss?

    • Different LNB mount?

    Thanks for your thoughts and suggestions.


    72/3 de DM5TU - sTef

    72 de sTef

    … -.-

    DM5TU / VY1QRP - DL-QRP-AG *GM* - GQRP #8769 - CalQRP #034 - NAP #1607

  • Hi Stef,


    as far as i can see on your pictures your feed ist not in the focus of the dish.



    With this arrangement i have no loss compared to the LNB without the POTY.


    Best regards,


    Wilfried

  • Hello Stef,


    my setup looks like that from OE9WLJ (POTY much closer to the mounting bracket than in your images) and I have only about 1dB "loss" compared to the LNB in the focus without the POTY. And like PA1EW already said the dielectric lens is not in the right postion.


    73 de Johannes

  • I see two issues, as others observe the lens isn't fully inserted, and the feed is not at the focus. The latter is really important, a few cm error will have a big impact at 10 GHz. You will need to modify the feed holder to get your 7 dB back.


    Mike

  • Hi Stef,


    Have a look in the install manual of the Poty.

    Not the feed from the LNB has to be placed in the focus of the dish.

    The Poty itself has to be placed in the focus.

    I hope this will help you.


    73 de Volker

  • Dear all,


    I needed to open that topic, because:


    • that topic was missed in the forum
    • I might not be the only one with that issue
    • and it is always good to get new opinions


    As I thought, all of your very helpful feedback is now giving me the confidence I was looking for. And I was right up to here with my ideas.


    Thanks, Volker, Mike, Johannes, Wilfried and Ed !


    It is like in real life.... Focus always focus :-) I will work on that. Now the duty for the very hot afternoon will not be hocus pocus, no it will be focus POTY.


    And yes the dielectrical lens is not installed right on purpose.

    Even the correctly installed lens is giving a gain of about 1-2 db. This is what my tests were showing.


    So here my ToDos:


    • Finding the dish focus for the POTY.
    • Will it be the entrance of the 10GHz feed horn - the dielectric lens/beginning of the copper pipe?


    Stay tuned for my reports.


    Thanks for now. 72/3 de DM5TU - sTef

    72 de sTef

    … -.-

    DM5TU / VY1QRP - DL-QRP-AG *GM* - GQRP #8769 - CalQRP #034 - NAP #1607

  • The WG of the Poty needs to be at the same place as the feed of the LNB was before. Exactly the same plane. At 10GHz its extrem sensitiv. 1cm mechanical mismatch is paid by loss of 3dB.

    It takes me a while with my 60cm prime focus. Now it works wonderful at fully waterresistant in an grey water tube which you can buy at the local stores (Baunarkt) . See picture below if my minimal compact system for portable activity.

  • Hi all,


    I have been doing some tests with 3D printed lens antennas provided by Malcolm, G0UHY. I was concentrating on the MER of the DATV beacon as a metric, but also recorded the strength of the CW beacon (noise floor is -115 dBm in 3.5kHz bandwidth). Here are the results:


    Culprit DATV Beacon MER CW Beacon
    Standard rocket Lens 10.7 -79
    Short cone 9.5 -80
    Long cone 10.1 -79
    Cylinder 9.1 -81
    No lens 9.6 -80


    The dish is a 2.4m channel master offset. It has a F/D of 0.6. The poorer performing lenses may be better at lower F/D, but I only have one dish so can't test this.


    Mike