Making a 1090MHz CoCo Antenna for ADSB 

Tack så mycket, jag hoppas att du gillar mina videor.

Thanks TO!

Great to hear!

Hola me queda duda que con el primer tramo de cable le cortas el trozo pequeño de conductor central ?

That's a great idea!

Can you explain more?

@@HACKPHILES the shirt buttons have the inner core passed through the holes. they stop the outer shields shorting. So one button is trapped between the sections of the coax pieces. ensuring no short can occur. use a button instead of electrical tape. HTH

Thanks!

Thank you! I am hoping that the 2m version isn’t terribly difficult to manage.

Thanks! I did use it a little, it is in the video. :)

I don't know if you need to have even numbers exactly but I *think* that in theory that is the only way that the impedance balances out. You might consider adding a 75 Ohm or 50 Ohm resistor between the center and shield of the top segment and see if that improves things in the odd number segment scenario.

16 segments has more gain but for my purposes the little bit of extra gain wasn't worth building to. One way to tell - built it and test.

@@LifeAtTerminalVelocity so I have around 250 segments will that improve the gain?

@@noobking5056 I have 251 segments. Works great.

@@Banditt42 size of each segment?

I haven't built the antenna for 146.5 but the process would be the same as for 1090MHz. Just with different length elements. For 144.390MHz using standard 75Ohm RG-6 it would be 430.83 mm per segment. I would use at least 8 segments.

@@LifeAtTerminalVelocity I want to use for TX & RX, so I think it will be 50ohms coax on this case right?

Yup. The length would be different because 50Ω Coax has a different velocity factor. You might also have to add a 50Ω resistor to the end for the SWR to come into where it needs to be.

@@LifeAtTerminalVelocity I will try to build it during this weekend, my only doubt is the topic about 50ohms resistor, is that like a stub for tune the antenna? thanks!

That is my understanding of it but I have never put it to the test.

I sure did and it works great. Never made a video about it because this video shows how to make the antenna. Didn't think duplicating the content wight a different length would serve a purpose.

no nothing.

I wish I could help you but without knowing the velocity factor you just have to guess. The alternative is to buy some cable who's velocity factor you know or can look up.

@@LifeAtTerminalVelocity I found a simlar cable like the one i have with same core material, insulation and shielding. I will use the velocity factor of that since it also has the same Ohms and pray for the best. Worst case i buy i new cable.

You should be able to google the vf from the cable data printed on the actual cable.

Excellent question! Keep in mind that I'm not an antenna theory expert and what I know about this design comes from what I have read when I was looking for a solution that was inexpensive. This is a set of stacked antenna sections on the same plane (Co-linear) made out of Coaxial cable (thus the moniker CoCo for Coaxial Co-linear). So the actual antenna segments are every other segment starting from the base. So if we number the segments sequentially the only real parts of the antenna are the odd number segments. We are using the shield of the even sections to transport the signal of the odd sections and the center conductor to transport the ground of the odd sections. Thus the velocity factor only matters in the sections that receive the signal. It took me a lot of reading to get to that point because I couldn't understand how the actual antenna worked given it theoretically is just one big continuous chunk of copper. Until you alternate the centers and shields. Wild ain't it? So use the vf of the coax you are using to build the antenna. It will work.

@LifeAtTerminalVelocity I'm dubious. I've built a few myself. Yes they work, but without some very expensive test gear it's impossible to tell how well they are working. Phasing issues could also arise with the differing vf. If we're not too fussed about being spot on, yes it's Ok. I've also seen multiple designs, with quarter wave stubs, quarter wave initial segments followed by half wave then topped with quarter wave. I may try modelling in AN-SOF but its a tricky one to build in a model.

Not expensive at all to get the equipment to test it. A NanoVNA is $61 - amzn.to/3pOj3Dy

@LifeAtTerminalVelocity I have one. Won't measure gain though.

Oh it will! Take it for a spin, you will get hooked.

No doubt, but since it needs to go inside a PVC pipe for support and use outdoors the electrical tape was sufficient for my needs.

You could probably fit the entire antenna in one big length of heatshrink for giggles.

You can head over to this link. Plug in the frequency and it will give you the length you need to cut each section. Assuming that your coax is RG6 your VF should be 83-86%. Coaxial Collinear Antenna Calculator - jeroen.steeman.org/Antenna/collinear-coax

@@LifeAtTerminalVelocity that link is dead

It's working today 4/10/2022

Hi Richard, I used 75Ohm Coax because it is perfectly fine for this application. I’m only receiving and not transmitting, the impedance match is not required and lets me make an antenna very cheaply. There is no matching unit or transformer as it isn’t necessary. I use the ADSBX Bandpass Filter, it is listed in the video that follows this one (Making an ADSB receiver). Your plan for LMR 400 is solid from what I can tell. Get your receiver up and running and have a blast with it.