Dielectric lens for f/d 0,35 primefocus dish any experiences?

  • I tryed to illuminate my portable G3RUH 60cm primefocus dish with my Poty Antenna rather unsuccessfully. The Poty works great on my 80cm offset dish with the Venton rocket lens. Any ideas or experiences with small primfocus dishes and low f/d (0,35)?

    73 Guntram, oe9dgv.

  • Guntram, are you in the focuspoint of the dish? Try to move the feed towards the dish,or away from it and look on the websdr for your uplink sig, for rx side use sdr stick+ program to see the difference.

    I have a patch for the uplink in a 60cm dish with f/D 0.4, and works FB for uplink, another same dish i also have here with a ve4ma waveguide feed for rx,but this feed has choke ring to meet the dish better.

    I can compare the 60cm with patch and my 95cm offset with dualbandfeed tomrrow if you like. 60cm should be less strong, in order +-2.5dB

    73's Jerry

  • Tnx Jerry, I will do that and report my results.. Its a good idea to test first the tx signal. The original G3RUH Patchfeed works very good with this dish and it`s possible, that I`m a lttle bit to close with my Poty. We will see..

    73`s Guntram.

  • oe9dgv Hi Guntram
    The 0.35fd may be OK for the 2.4GHz section as the POTY over illuminates a 0.6fd dish.
    However, the gain of the dielectric lens on 10GHz is too high for a 0.35fd. It will only illuminate a small section of the dish. You may have better results with an open waveguide feed. Try setting the focal point....take an RX measurement, then remove the lens and measure absolute beacon signal strength again.

    73


    David

  • In addition to Davids correct statements (S-band section somewhat over illuminates a f/D = 0.6 dish etc): bear in mind that when you optimise the 10 GHz part with lens and subsequently remove the lens (which is favourable for lower f/D ratios) you have to realign the feed because the phase centers of the dielectric lens and open waveguide differ. With the lens the phase center lies more 'out of the waveguide' compared to an open waveguide.

  • I would try again but without the lens. This should be OK for 10 GHz. The S-band will be down a little but not too bad. The phase centres on both bands will be close together. See HB9PZK's comments on this forum and at https://rfantennas.wordpress.com/author/hb9pzk/


    It will be about 50% efficient on S-band and 60% on X-band. Can't complain for two bits of brass and a copper pipe.


    Mike

  • After some days of delay (high temp. on my balcony) I got today acceptable receiving signals with poty and my 60cm primefocus dish. I had to increase the distansce to the dish but its better with lens. The CW beacon is 21 dB over the noise, that seems acceptable for me.


    For transmitting I will try it with a chock ring (a camembert boxing with alu film at the side?). I will report abt success.


    73`s Guntram oe9dgv.