POTY vs HELIX

Well OK - but the POTY was never intended for long focal length dishes so it's not surprising a helix does better. What is the F/D of that dish? It looks like 0.7-0.8 which makes sense for a 4.5 turn helix.

I see have a VNA so why show VSWR ? It only gives you part of the picture. It simply perpetuates the myth popular amongst HF operators that VSWR is all that matters. It's a parameter but not the only one and not even the most important. We are better than that. From the VSWR I can't tell if the patch is tuned correctly, which will make up to 3 dB difference in the uplink it it's linear instead of circular. The other thing about that POTY is the reflector is not the recommended 105mm circle. It might be OK. I don't know.

What is surprising is the difference on receive. The Helix should be worse but given that's not the recommended Lens on the POTY. I have never recommended anything like that, I can't see how it could work. If you don't follow the instructions, it won't work so well. HB9PZKs design is several dB better, as it the originally recommended Rocket Lens. If it really is so very many dB worse there is something not right - like the focal position or the wrong lens, or both. The feed looks too far forwards but that's not easy to tell from the Photo. The gain of LNBs varies widely so it's signal above noise that matters. A number in dBm is meaningless without knowing the gain. Was there some gain calibration done here?

Mike

I can confirm, that I have seen a 3 dB difference between the Rocket-lens and this lens delivered with the POTY on a 0,66 f/D-dish on receive. For NB-usage it will not make a big difference, but for DATV-usage.
Gerhard

Very interesting - but the focus of the POTY is not in the same place as the reflector but in the middle of the lens, so it needs to move a few mm back. This is probably why it is worse. That's a challenge mechanically with that feed arm because the reflector gets in the way. The Rocket lens might be better. did you measure the F/D ?

I do agree with G0MJW. The problem is that you can not put the lens of the POTY into the focal point of the antenna as you do with the LNB its self. Therefore the reception is poorer than the one made only with the LNB. As for the Helix I have not tried yet, but it looks that the cap of the LNB is closer into the focus of the dish. Therefore we should expect better reception than the one with POTY.

lnb adaptor shopuld be made excentric

... that gains you a bit of height