Dual Feed For Uplink / Downlink

LZ1JH can you show how you made the 4-way splitter and impedance matching?

I presume the 4 antennas are ~50ohm impedance so these somehow need to be matched.

Hello Hans-Jochen,

The individual antennas are made directly from the feeder RG 141-50. The elements are made of copper wire with a diameter of 1,5 mm. The director has a length of 51 mm and a reflector with a length of 61 mm. The distance between them is 30 mm. Fiders must have the same lengths. They gather at a point where the impedance is 12,5 ohms. To match 50 ohms lines, a 25 ohms 1/4 lambda transformer is needed . This is very easy with two pieces of RG 141-50 tailored to the shortening coefficient. For this cable is 0.7. The most important thing is to properly connect dipoles to get LHCP. I showed it on the attached picture. For proper connection, LZ2US helped me a lot. The best SWR I received is about 1,2.

73 Rumen LZ1JH

Hi PA1CHL ,

So the individual antennas are 50 ohms. This is described above. I apply a photo of the splitter.

Ok I understand!

I am planning to try with 2 circular patch antennas alongside the LNB so I need a 1:2 splitter which I want to do that way but of course the impedance of the match will be 35 ohms so it will have to be done a bit differently.

Nice to see that your antenna works, maybe I will try that one as well.

Hi,

Two antennas best fit with 75 ohms feeder pieces. However, in order to obtain polarization, it will be necessary to have 1/4 lambda spread. If not to work with the transformer. This is very well explained here: https://www.qsl.net/sv1bsx/antenna-pol/polarization.html

This feed seems to me better than a helix one because I think it's a little overshadowed by the LNB at 10 Ghz. Helix is right ahead LNB. And yagi are around him. But I think so I can be wrong .

73 Rumen LZ1JH

Yes of course 75 ohm is OK for this too, I have done that in the past to have circular polarization with a crossed yagi.

My planned experiment is to have two circular polarized antennas alongside the LNB and see if that results in proper pointing.

Indeed I also want to avoid shadowing. For QO-100 NB it may not be important (I can afford to lose some signal) but I use the same antenna for TV.

Quote from G4EML

The length of the tube is not critical. It is acting as waveguide which has a very low loss.

The differences in the inner diameters will work OK. Ideally it should be a smooth transition but a small step will not introduce much loss.

Yes - it works with prime focus - 0.5 f/D

PA3FYM  G0MJW I have a question regarding the dual band patch antenne. How critical is the diameter of the reflector (105mm). For installing the antenna in a dn110 pipe this dimension is a little bit too large (1mm) .

DL5MGD Relative to the patch dimensions the reflector plate is not that critical. So 104mm diameter (I reckon it fits inside your DN110 pipe then?) will do fine. Perhaps you loose a milliBell gain (i.e. the radiation pattern) ; -)

PA3FYM Thanks!!! 104mm are ok.

@LZ1JH How do you measure your SWR ? any poor man GHZ radio testset ?

Quote from Remco

Founding father of this feed is G0MJW and I assisted with finding the right feed point to let it produce CP. It is modelled in CST Studio and a MP4 movie of the simulations canbe seen here . Will try to find the picture of the dimensions.

In the meanwhile you can look at these ones here or here or here or here or here : -)

Edit: below the dimensions of the feed. Spacing between patch and reflector is 3mm. I have the feed point at X,Y = 8,28 and a cropped square reflector.

2300 - 2500 MHz simulation done by G0MJW is below. It confirms the right position of the feed point is critical for CP, i.e. balloon perfectly circling around Z = 50 + j0 Ω ! :

Display More

Would it change alot if the reflector had a diameter of 95mm?

I have a number of old hard disk platters, but they are smaller. Yet my karma would benefit from the reuse some stuff from my junk box.

iz2eeq It works but the radiation pattern will be broader (larger opening angle) but it is worth a try ! However, the diameter of the hole is around 25mm, correct?

PA3FYM yes, correct... should be an almost perfect fit for the copper pipe with an internal diameter of 22

iz2eeq No, the copper pipe must have 22 OD and 20 mm ID (standard plumbing pipe). So your hole is too large.

PA3FYM either I found a way of filling the gap or the shiny discs will get back to sleep in the junk box.

DN1HRZ SWR It has good values.

Hello everyone, i have a question about the material that can be used to assemble patches and helices reflectors... since I'm having a hard time finding a copper or brass foil supplier, would it be possible to use pcb to build those parts? What would be the effect of a double sided pcb FR4 at these frequencies (supposing that the patch and the reflector are made of pcb for example with the two sides connected together). Maybe it's a newbie question but that's what I am after all 😊. Thank you!

I made other patches from FR4 PCB but the small spacing between the plates makes it difficult to solder the inner surfaces to the copper pipe.

But there is hope! M0EYT makes his patches from 36mm OD copper pipe. He anneals it, cools it red hot in water, sledges it with a hammer and CNC's it. He already send out about 50 (or may be even mode) plate pairs.

Quote from Remco

I made other patches from FR4 PCB but the small spacing between the plates makes it difficult to solder the inner surfaces to the copper pipe.

But there is hope! M0EYT makes his patches from 36mm OD copper pipe. He anneals it, cools it red hot in water, sledges it with a hammer and CNC's it. He already send out about 50 (or may be even mode) plate pairs.

Oh my, that's where blacksmith meets ham