3D printable Rocket style lens for QO-100 POTY feed

[Pheonix2024]

I have designed this Rocket-style lens which works extremely well. I've tested it with PLA and PETG so far. The latter is marginally better performance-wise and very close to the original (within about 1/2db).

N.B. Both parts are required to make the complete lens.

The links are here:

https://www.tinkercad.com/things/02jCBf ... l-required
https://www.tinkercad.com/things/hJLUVs ... l-required

IMG_1292.jpg (33.81 KiB) Viewed 158430 times

Greg
G4CST

[g0mjw]

Good work Greg

Note for it to work the material needs to match the electrical characteristics of the original. Do we have any idea what the original is made of?

Mike

[Basil]

Thanks for sharing your work.

Although I do not use a lens myself I am curious to learn how they work and how different plastics affect their performance. Can anyone offer a link to a reasonably mathematically simplified explanation of how they operate please?

[radiogareth]

Mike, as a guess (without burning a tiny sample) I'd expect them to be HD Polythene. Polypropylene has poor UV resistance (maybe they don't care, or even prefer it as you would then need a whole new LNB...) and the wonders of cheap mass produced plastic outweigh any benefit from using an engineering plastic.
As to how they work, I have no maths but they work like different refractive index glass does with light. I accidentally discovered this when my son used some white nylon to act as a plug on the end of some 22mm copper, but fitted it with a white LED. I expected the light to continue pretty much as the LED sent it, but it turned it through 70-80 degrees and the light emerged and made it look like a lighthouse - the end of the nylon was a tapered cone.
Update...just touched a red rocket lens with my Weller barrel and I think its Polypropylene. I went on a course run by the British Plastics Federation in 2000 and it was part of the course - burn a bit!! (I had however experimented much earlier in life with burning orange plastic baler twine....)
See https://www.boedeker.com/Technical-Reso ... E2GXvk2ZXZ
Thanks for sharing the .stl's
Gareth

[g0mjw]

If it is polypropylene it will have a relative dielectric constant (Er) of 2.2 to.2.6, lets say 2.4 and a pretty low loss tangent so good for a lens.

Polytetrafluoroethylene (PETG) has an Er of 2.4 with a bit more loss. A fairly good match and easy to print with.

Polytetrafluoroethylene (PTFE) has a lower Er around 2.2 and low loss. Not as close and impossible to print with.

Polylactic acid (PLA) has a higher Er, around 3.2 but who knows what fillers are in there. Not a good match

Polyvinyl chloride (PVC) has an Er of about 3 - not a good match. Ditto ABS

So PETG is the one to use. Interestingly, Rexolite has a Er of 2.5 and low loss. HB9PZKs lens might also work and would be easier to print.

Mike

[Pa3fbx]

next big question.. for what F/D is this lens...

Benno

[g0mjw]

Yes Benno, it is a good question. Maybe someone with access to a simulator could simulate it. It is too complex for the student version of CST.

Here is an unusual use of 3D printing software that gives you some idea how these lenses work.

Screenshot 2025-03-12 202910.png (272.27 KiB) Viewed 157874 times

What we don't know is the dielectric constant of the plastic used. Also how accurate is the STL model?

Mike

[G8IKP]

When this design is proven could we get some in the BATC shop for members to purchase ? I would be very interested in getting a better lens for my POTY's. I'm sure the club would get some good income from these. John G8IKP

[Basil]

The 3D rotatable image helps a lot, I had no idea they were 2 piece with a complex internal structure, I'd wrongly assumed them to be solid plastic, thanks all.