Mounting of POTY on dish, SWR high, how to fix?

  • @I0LYL

    @G0MJW

    @DD4YR


    I just heard my downlink on the web SDR! The main problem was that the prior owner of the FT817 had set the menu for the front antenna jack, and I am using the SO-239 on the back, bad mistake by me to overlook this. Now all LEDs are green. Thanks to all for the help.


    Now, does anyone know how I can mount the LNB and the BamaTech feed on one dish? I originally thought I could insert the feed into the LNB, as in photo A below. But Markus at BamaTech told me this would not work with his duo feed, I would need the feed shown below in photo B (130 euros). I was also told I could not use a dual holder like the one in photo C, because this holder points each feed at a different satellite. It was suggested that the easiest and cheapest way to proceed would be to buy a second dish.

  • Now, does anyone know how I can mount the LNB and the BamaTech feed on one dish?


    Yes, take a look here in this thread ...:

    Downconverter für BaMaTech Dualband Feed



    I was also told I could not use a dual holder like the one in photo C, because this holder points each feed at a different satellite.

    That´s correct. Did not fit.


    73 de Robert

  • Yes, take a look here in this thread ...:

    Downconverter für BaMaTech Dualband Feed

    Thanks again, Robert. I'm not sure the owner will allow me the cut the feed, but good to know it is possible.


    In the meantime, for a poor man's solution, a local ham told me I could just tape the feed on top of the LNB. I was skeptical but gave it a try, see attached photo. I was able to make a QSO with DL4RS. He said my signal was weak (-80) but readable. Maybe with some adjustment I can improve the signal. Has anyone tried anything like this, perhaps a more sophisticated version?

  • Well, according to the motto: something always works ...

    as long as the feed is mounted outside of the reflected beam path (i.e. next to or above the LNB), a loss of several dB will occur because the main lobe of the emitted signal is simply not directed towards QO-100.

    To make matters worse, this type of patch antenna (BaMaTech or POTY) has an opening angle that is too large for an offset dish. The mirror is considered "overiluminated", which creates additional losses. (So, a lot of Ham´s use helical feeds in offset dishes instead a patch antenna)


    Remember, with a 20 watt signal from the SG-Lab PA you can easily trigger the LEILA of the QO-100 with a 70cm offset dish, i.e. generate too much transmission power.


    Anyway, not a good solution.

  • Well, according to the motto: something always works ...

    as long as the feed is mounted outside of the reflected beam path (i.e. next to or above the LNB), a loss of several dB will occur because the main lobe of the emitted signal is simply not directed towards QO-100.

    Anyway, not a good solution.

    Yes, Robert, I tried several different positions for mounting the feed next to the LNB and as you say all were lossy. And the owner of the BamaTech has asked me not to cut off the bottom or otherwise modify the feed.


    So this seems to leave me with 2 options:

    1) separate dishes for TX and RX, or

    2) buy the dual band feed with LNB for 130 euros (photo B above).


    Does anyone have a used dual band feed with LNB for sale?

  • Instead you could use a non-LNB solution based on a 10 GHz receive converter. It might be cheaper to spend 40 Euro on a POTY kit.

    DB6NT ? Several people have re-tuned transverters I believe. Of course the cost is quite high but there must be thousands of old 10 GHz receive converters lying around that are no longer used after the OM upgraded or lost interest in microwaves. You can of course also just modify the LNB with an SMA rather than the probe but that's quite advanced and needs skill.


    Mike

  • there is a 3rd option (which I would prefere) :


    Buy a POTY feed, then you have all the advantages you need.

    You can still use your LNB

    Is that a POTY in the attached photo? It came in the box with the rest of the QO-100 gear that has been loaned to me. Is it a POTY with the inside of an LNB attached to the bottom? That LNB does not work, I've tried it. Maybe I could remove it.

  • Is that a POTY in the attached photo?

    Yes, it is ! (nearly) :-)


    remove the LNB and add your or a cheap new LNB


    My solution is this:


    Montage POTY an Opticum LNB LSP-02G - QO-100 / Es'hail-2 / P4-A (deutsch) -  AMSAT Deutschland e.V. Forum


    by the way, you need a electrical lense (this black part in the waveguide) for better results in an offset dish.

  • How do I remove the broken LNB? Can I do it with a soldering gun or do I need a blow torch? I can't tell if it is glued or soldered.

    Try to heat.

    Glue will also go weak if you heat up.

    In worst case, you can take a saw and remove the LNB

    Its no negative effekt if the wavegun from the POTY is shorter

  • The POTY construction looks ok. Nearly 4mm. Is ist home built?

    I did not build it but it looks home built.


    Do I need to break apart the plastic outside of the LNB or is there a trick to opening it? I've been trying to pry it open with no success.


    I can't remove the old LNB with soldering gun, will need to borrow a torch or cut it off as you suggested.

  • Do I need to break apart the plastic outside of the LNB or is there a trick to opening it? I've been trying to pry it open with no success.

    The two sides are clipped together.

    You have to find the clips by pressing and with a knife or scewdriver you can delock the clips.


  • The two sides are clipped together.

    You have to find the clips by pressing and with a knife or scewdriver you can delock the clips.

    OK, thanks, I got it open. But this LNB is square, not round like the broken one. It won't fit in, is there some way to use it?