POTY tuning

  • I made some tests with the POTY feed. I made a small cone using 0,06mm aluminium foil. The foil is from a alum. plate you’re using when you like to make a pie in the oven. What I notised in Gqrx signal scale ( left side of the spectrum) was, that with that cone both rx and tx was 5 units smaller and overall noise stayed very same. The photos shows silver coated POTY with and without the alum. cone.


    73 de ismo

  • If it is 5 S units worse with the cone (-30 dB!) pie cooking remains the best use. I wonder if your post is written incorrectly?


    Such a cone will act as a horn at 10 GHz, it will focus the beam to a better match to a longer F/D - this is what the lens does as well. However, it will also move the 10 GHz focus much further forward and this would require correction but then the 2.4 GHz and 10 GHz focii would be too far apart requiring you to optimise for one band or the other.


    Silver plating won't make much difference but it does look nice.


    Mike

  • I don't know what units they are in the left side of the Gqrx spectrum, but with the aluminium cone NB cw beacon rises more up, like from 62 to 57.


    br ismo

  • Ah - so the numbers decrease with increased SNR. They will be dB below the maximum and 57 is 5 dB better than 62. They are not S units. That's more like I expected. I would try a shorter cone but the same final aperture and see if it is the same. Up to 40mm diameter and see if it impacts the S-band pattern. You can't tell by the match, you need to look at the level of your TX over the transponder nose floor. Also the noise floor should increase because you are seeing transponder noise.



    Mike