having issues with a helix antenna

[m1cdq]

Im building this antenna on thingiverse
https://www.thingiverse.com/thing:3903285

featured_preview_Universal_Screw_LNB_3D_printed_Helix_v1_2000[1].jpg (21.8 KiB) Viewed 4138 times

featured_preview_20191203_100518[1].jpg (38.3 KiB) Viewed 4138 times

When i place the antenna over the lnb Im losing rx signal
I can stick just the dome cover over the lnb and this does not effect the rx signal
I have also retested the PLA in the microwave and no heating of filament
If i just mount the reflector over the lnb no loss of rx signal. but if i mount the helix to the reflector mount and place on the lnb I lose signal
The oscar 100 wb beacon in normal setup Im at a mer of 7.2 on a 1m ofset dish. LNB is a quad octogon pll lnb
with the 2.4ghz mounted the mer drops to 3 and not signal lock.

any suggestions

[g0mjw]

It's hardly surprising there is loss when you put a metal coil in front of the LNB. This is why I developed a dual band patch feed.

[G4WIM]

I understand that Dave G3ZGZ uses a similar feed which appears to work ok but pretty sure his helix was shorter to lessen the 10GHz signal loss.

Try contacting him for details ?

However a shorter helix may not create a truly CP signal.

Concensus is to use a POTY for best results.

73 Tim

[radiogareth]

Interesting discussion. I think I read that the original designer of the Helix assembly found a 1dB improvement over his POTY with this design but anything conductive in a RF field is going to change things......
Gareth

[m1cdq]

Im chatting with the original designer.
It could be i have the only dish that dont like this type of feed or I have done something wrong that is so obvious i cant see it.

Its all about being a ham. try it to see it it works if not then why , how to improve or fix. or try something else. its all fun

[G8GKQ]

Roger

My gut feeling is that the 4dB reduction in SNR that you are seeing when you put the 3 turn helix in front of the LNB feed is exactly what I would expect.

Was the original designer using it for DATV or narrow-band? The link budget for the narrow band transponder is so generous that 4 dB would not be a problem. Not so for the wideband transponder - it is much more critical.

Dave G8GKQ