Dual Feed For Uplink / Downlink

  • Hello Hans-Jochen,

    The individual antennas are made directly from the feeder RG 141-50. The elements are made of copper wire with a diameter of 1,5 mm. The director has a length of 51 mm and a reflector with a length of 61 mm. The distance between them is 30 mm. Fiders must have the same lengths. They gather at a point where the impedance is 12,5 ohms. To match 50 ohms lines, a 25 ohms 1/4 lambda transformer is needed . This is very easy with two pieces of RG 141-50 tailored to the shortening coefficient. For this cable is 0.7. The most important thing is to properly connect dipoles to get LHCP. I showed it on the attached picture. For proper connection, LZ2US helped me a lot. The best SWR I received is about 1,2.


    73 Rumen LZ1JH


  • Ok I understand!

    I am planning to try with 2 circular patch antennas alongside the LNB so I need a 1:2 splitter which I want to do that way but of course the impedance of the match will be 35 ohms so it will have to be done a bit differently.

    Nice to see that your antenna works, maybe I will try that one as well.

  • Hi,

    Two antennas best fit with 75 ohms feeder pieces. However, in order to obtain polarization, it will be necessary to have 1/4 lambda spread. If not to work with the transformer. This is very well explained here: https://www.qsl.net/sv1bsx/antenna-pol/polarization.html

    This feed seems to me better than a helix one because I think it's a little overshadowed by the LNB at 10 Ghz. Helix is right ahead LNB. And yagi are around him. But I think so I can be wrong ;).

    73 Rumen LZ1JH

  • Yes of course 75 ohm is OK for this too, I have done that in the past to have circular polarization with a crossed yagi.

    My planned experiment is to have two circular polarized antennas alongside the LNB and see if that results in proper pointing.

    Indeed I also want to avoid shadowing. For QO-100 NB it may not be important (I can afford to lose some signal) but I use the same antenna for TV.

  • The length of the tube is not critical. It is acting as waveguide which has a very low loss.

    The differences in the inner diameters will work OK. Ideally it should be a smooth transition but a small step will not introduce much loss.

    Yes - it works with prime focus - 0.5 f/D

  • DL5MGD Relative to the patch dimensions the reflector plate is not that critical. So 104mm diameter (I reckon it fits inside your DN110 pipe then?) will do fine. Perhaps you loose a milliBell gain (i.e. the radiation pattern) ; -)

  • Would it change alot if the reflector had a diameter of 95mm?


    I have a number of old hard disk platters, but they are smaller. Yet my karma would benefit from the reuse some stuff from my junk box.

  • Hello everyone, i have a question about the material that can be used to assemble patches and helices reflectors... since I'm having a hard time finding a copper or brass foil supplier, would it be possible to use pcb to build those parts? What would be the effect of a double sided pcb FR4 at these frequencies (supposing that the patch and the reflector are made of pcb for example with the two sides connected together). Maybe it's a newbie question but that's what I am after all 😊. Thank you!

  • I made other patches from FR4 PCB but the small spacing between the plates makes it difficult to solder the inner surfaces to the copper pipe.


    But there is hope! M0EYT makes his patches from 36mm OD copper pipe. He anneals it, cools it red hot in water, sledges it with a hammer and CNC's it. He already send out about 50 (or may be even mode) plate pairs.

  • I made other patches from FR4 PCB but the small spacing between the plates makes it difficult to solder the inner surfaces to the copper pipe.


    But there is hope! M0EYT makes his patches from 36mm OD copper pipe. He anneals it, cools it red hot in water, sledges it with a hammer and CNC's it. He already send out about 50 (or may be even mode) plate pairs.

    Oh my, that's where blacksmith meets ham :D