My experience with the DXPATROL feed for QO-100

In 2023 I wanted to become QRV on QO-100 and for this I did buy some equipment from DXPATROL

I did buy the DXPatrol groundstation and the DXPatrol Helix antenna

I wanted to use a 80 cm offset dish for this system and build everything together.

After all was installed I had to align the dish to the satellite which was not a big problem

Picture of the feed, mounted LNB and on top the DXPATROL Helix

The received signals from the satellite were good but the signal from my uplink was very weak.

I measured using the WEBSDR : https://eshail.batc.org.uk/nb/ my own signal at a level of -84 dB and only 6 dB above noise.
That was quite disappointing and I started to check all system parts and coax cable's used if they were the reason for the weak signal.

I mounted a better coax cable for my uplink and gained about 1 dB, still not good enough.

I measured the return loss from the DXPATROL Helix but found this to be OK.
Looking at the Helix I became suspicious at it but not yet convinced that this was the problem.

I decided to get me a bigger dish and bought me a 1 mtr Gibertini offset dish.
When this was installed it still was not good, my signal was now at a level of -80 dB at the Websdr.

Then I started to search for some information (specifications) of the DXPATROL Helix but I did not find any information from it other than VSWR.

I searched for technical information and found some online tools to calculate a Helix antenna.

The helix from DXPATROL has about 2 winding, so for start I calculated a helix with 3 windings

The Helix from DXPATROL

These are the results from the online calculator : https://jcoppens.com/ant/helix/calc.en.php

Important parameters are D and S and the beam width. Looking at the DXPATROL helix the helix itself is not good for the design frequency 2.4 GHz.
Also a helix with only 2 windings, if it was designed for 2.4 GHz, is not good for feeding an offset dish reflector.

I did the Helix calculations for helixes between 3 and 8 windings, results were as expected that more windings do not change the parameters D and S and that more windings only have effect on the Beam width.

I decided I wanted to build myself a helix with 7 windings and try this on the QO-100 satellite.

Calculation results for a 7 winding helix

I build this Helix to see how it performed in my system

The signal via the satellite was at max at -72 dB which is 7 to 8 dB better than the DXPATROL helix

Problem with this home made helix is that the end of the helix is not longer at the focal point from the dish.

I then searched for a helix with some less windings and also a way to build is weather proof.

I found a design by Nolle engineering and decided to go for that as it had a very nice weather protection radome
I ordered this one: https://nolle.engineering/product/icfv2/

After receiving the new Helix from Nolle engineering I measured return loss which was excellent, then I mounted it in the dish.
I did my uplink test, resulting in a level at - 68 dB a big improvement

With this new feed the performance is 12 dB better than with the DXPATROL feed.

It was obvious that the DXPATROL Helix is not performing as it should. It is performing 12 dB worse than a good designed feed.