POTY and return loss plot

  • Just to be clear - I was joking about the polishing - however over time brass and copper tarnish and this might impact losses a little, so it's worth taking steps to protect from the weather. A light coat of clear lacquer is an alternative. It won't impact performance though it might move the match a little.

    Let us know haw you get on.


  • The POTY also have a 10 GHz "side". I have measured LNB performance with the original LNB feedhorn and with the POTY feed on the LNB - after cutting off the original horn.

    First measurement is Y-factor (difference in cold sky/hot ground).

    Original feed: 4.9 dB

    POTY (without dielectric lens): 3.7 dB

    POTY with dielectric lens: 3.3 dB

    Second measurement is transponder noisefloor (60 cm offset dish)

    Original feed: 2.9 dB

    POTY with dielectric lens: 1.8 dB

    Noise measurements are done with averaging, so accuracy is about 0.1 dB. Both Y-factor and transponder noise floor involves other parameters than just LNB NF or antenna gain. So there is no direct one-to-one dB relation to the POTY performance.

    The degradation in performance with the POTY is measureable, but any dual band antenna is a compromise. This is compensated by only having to use one antenna.

    Anyone else with similar observations?

    73 Ole

  • Hi Ole,

    I have not the exact values, but I agree with your finding. I am using Zircon L101ECO LNB, there is no need cut original horn - there is open waveguide with lens in original. LNB fits to pipe after small circumferential grinding. I have noticed some degradation of LNB performance with a new extended open waveguide. I have tried use POTY without lens - there is the worst result. With a new 3d printed lens it is by around 3dB better, but not still as LNB in original. Unfortunatelly I have lost original lens, I can not try it.

    For NB is not some small loss so important, most of the signals are very strong, but for WB DATV reception is every dB important, I think.

    I have got another LNB with very long waveguide. There is very interesting lens at the beginning of waveguide. I will try it.

    73 de Pavel OK1PHU

  • Ole this is very useful information What is the F/D of your dish - I am surprised that no lens in better than with lens. This would be true for a dish with an F/D under 0.4 ish, but not for a longer focal length.

    It's also not a lot to lose but nice if we can get it back with a better matched lens.



  • The supplied lens with the POTY-kit is my '2nd attempt' for a lens. It worked/s better than the first attempt (this was a smaller lens) and improved SNR with around 3-4 dB compared to the open waveguide in conjunction with a f/D = 0.6 60cm wide dish.

    I still have an original Rocket LNB lens which performs (still) the best.

    I received a prototype PTFE PZK-lens and will measure that later on.

    It also seems that (in my case!) under illuminating the dish improves SNR because

    the overspill does not look at 'warm' objects.

    Anyway, lots of experiments to improve the station .. which is part of the fun imho

  • Hi Mike, G0MJW - my dish is a 60 cm TRIAX with f/D 0.6. My measurements does not show that the POTY is better without the dielectric lens - on the contrary, as others have reported. When I assemble my next POTY, I'll measure the lens effect more closely.

    My Y-factor measurement was done on POTY both with and without dielectry lens. I make these measurement on the LNB+feed combination alone - so no dish involved. Ideally the Y-factor should not change from narrowing the beamwidth, as long a the LNB sees either cold sky or hot ground within the actual beamwith. I believe the small reduction in Y-factor with the lens is due to losses in the dielectric material. (theoretically could also be due to changes to side-/backlobes)

    73 Ole

  • OK, the news is out (see my previous posting). Received nr 1 and nr 2 from Hans this evening. Just inserted nr1 and nr2 here. Compared to my benchmark (nr3) nr2 is on par and presumably somewhat better. However, the NB-tpx beacons are suboptimal to do absolute measurements due to QSB (can be 3 dB) and non-FSK (for the CW-beacon) and/or varying amplitude of the PSK-beacon.

    I decided to leave nr2 in to perform longer term measurements.

    Having tested around 13 different lenses, nr2 is an outlier in a positive sense!

  • As promised here a short feedback to the Poty antenna i soldered at the wrong side. I resoldered the patch and after a smal tune (by optimizing the patch reflector distance) the measurement was fine - 20dB S11. First test gave me better results as before with the helical antenna. I need to reduce the output power now

    For me its one of the best solution - electrical and mechanical.

    The spurs were still there - it tuned an old interdigital filter (see picture) and the problem with spurs/harmonics were solved.

    Thanks for that nice antenne - next challenge to make it water and winter restistance.

    73 Kai DH0SK

  • Hello,

    I now have my poty ready with a very nice RL-curve and it works very well.

    Now I wonder if anyone has experience with covering the POTY with a thin coat of (non conducting) paint to protect it against corrsion.

    Is the influence of the covering paint significant ?

    I ask, because I tuned my POTY with a piece of dielectric material (thanks to Pavel OK1PHU), thus I suggest that there is an influence even of a thin layer of any material.

    73 de Johannes

  • DL5RDI Johannes the main issue is if it is raining and you have waterdrops between the plates. That is not nice..then the signal goes down dramaticaly. you should protect the POTY for rain and snow if it is in the weather eg. in the garden or on the roof..:thumbup:;)

  • DD0KP Hello Heiner, Looks like a great solution!. Though, I am curious about possible extra attenuation to the 2.4GHz patch radiator from the PVC material?. I recall reading some negative reports about PVC for this use.

    When possible, please tell us what you measure without- and with this PVC cap.


    73 Ed