BATC Forum

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

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.

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

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

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

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