FlightAware Discussions

Mag Mount Antenna's Whip Replaced By V-Stub Wire Collinear

An honorable objective, but never stated.
Until proven otherwise, should we agree the CoCo should be done right or not at all?
If that means it’s not a beginners project, so be it.

Interesting cable - should be easy to work with, but be aware that even the black may not be UV stabilised (unsuited to outdoor use)
Could I suggest a 50 Ω may be an easier choice.

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Maybe. I don’t know. Why? I’m complete amateur with radio and etc.
I already ordered 75 Ω and it will be next to window or attic so no issues with UV. Do you have link to 50Ω?

Cheaper shipping here.

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Much coaxial cable is of unknown origin. Even what appears to be legitimate cable may be counterfeit. For an application reliant on velocity factor, such as element lengths in a coaxial collinear antenna, knowing the actual velocity factor (VF) is essential.

Measuring coaxial cable VF is relatively straightforward with a vector network analyzer (VNA). The following example was performed at HF, but the exact same technique can be used at higher frequencies, using a shorter length of cable. Coaxial cable VF does not usually change much with frequency, so it isn’t necessary to perform the measurement at 1090 MHz.

Caveat: in order to obtain an accurate VF measurement it is essential to establish the VNA measurement plane, aka calibration or reference plane. For new VNA users, this excellent tutorial explains VNA calibration.

Although coaxial cable VF measurement can be performed with a lower frequency VNA, such as the original NanoVNA used in the above tutorial, I would encourage ADS-B hobbyists to obtain a VNA capable of at least 1090 MHz so that completed antennas can be measured. With a 2-port VNA, filters can be characterized as well. I believe the NanoVNA V2 is currently the least expensive 2-port VNA suitable for 1090 MHz (it works from 50 kHz to 3 GHz).

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Agreed.
As the title of this thread is completely different from CoCo, it is better to either create a new thread dedicated to CoCo, or use an existing thread dedicated to CoCo.

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Here are some great calculators for those who may be interested in nerding out. In specific to where this thread is going, about 3/4 down, look for Velocity factor solver. This will help those following along with the links @nu3e kindly pasted.

@geckoVN
@gtj0
@Nitr0
@nu3e
@theresjam
@vkirienko
@wiedehopf

I have created a new thread dedicated to CoCo. You may please post about CoCo there. Thank you.

Coco (Coaxial Collinear) Antenna - Tips & Tricks

 

 

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It’s a matter of convenience mostly - 50 and 75Ω connectors tend not to be interchangeable. Avoiding adapters is best if practical.
Generic dongles tend to have 75Ω connectors, while brand name dongles tent to have 50Ω. If you are using a purchased 1090MHz antenna, it’ll probably have 50Ω.
Of course if you are building from scratch, use whatever is convenient!

The Wheeler version of COCO found its way into commercial production in the 460-MHz range.

The antenna used a dielectric housing for support of the somewhat floppy coaxial cable and for weather protection. To place the antenna at DC ground relative to its mounting location, the top section used a short between the inner and outer conductors at the ¼-λ mark, although the section continues for the full section length.

Along the base section, also a full electrical half-wavelength, the makers installed three ¼-λ rods connected to the coaxial cable braid 1/4-λ from the bottom of that section. However, section continues below the rods for its full length.

The feedpoint — close to 50 Ω in the antenna described in the article — is at the base of the lowest section.

Source:
Is COCO Your Cup of Tea?
By L.B. Cebik, W4RNL

http://on5au.be/Cebik-2/IsCocoYourCupOfTea.pdf

 

From ARRL Handbook

Lots of conflicting information above (no offence to anyone). I’d love to see top to bottom (bottom to top?) instructions from those who have had success with the design. VF’s are one thing, actual logical construction is another. I’m glad we have a dedicated thread now to unleash the experience from those who have success.

Not only above, but every where on the web, and much more conflicting.

Next to VF, this is the 2nd key hurdle in successful Coco making

Yes, that will be great. As far as I know @theresjam and @vkirienko have built successful cocos. It wil be great if both of them (and also any one else with a successful coco) can post full details of their built in the newly created dedicated thread.

Probably best not to try this if you have bias-T turned on and no DC isolation.

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In order to bring the off-topic discussions back to the original topic, here are some sketches & photos of the V-Stub wire collinear antenna. Back from coaxial collinear to wire collinear :wink:

Vspider-built-3

 

 

That and some illustrations use a balancing resistor with zero mention of blowing things up if you have power coming up the line. Hence the conflicting and rather shoddy information. I’m on the learning side of this one - my attempts all sucked and I knew the VF and am rather OCD with construction otherwise, so I blame the directions to keep my ego intact.

ACK - wrong thread - this isn’t the new one. Sorry.

I have posted the two configurations to highlight the issue of conflicting and incomplete information available on web in heap. This is very confusing for almost any one, particularly for a beginner.

No problem, it is OK.

 

Well, I got VLad up to the roof today and found that he does NOT like heights. At deck level where I was testing him, he did very well tracking about 50 aircraft (good for the time of day). As I raised the platform from deck-level to roof-level he slowly tracked fewer and fewer aircraft until it was only 4 at the roof line. I thought maybe the connector had loosened or maybe even the cable pulled out of the crimp (even though it was well supported) so I started lowering the platform. Sure enough, as I lowered it, more aircraft popped back in until it was back to around 50 again. Hmmm. So I wiggled all the connectors, raised it again and played with adding another filter and adjusting the gain but to no avail. On a hunch, I brought it down and replaced VLad with the Mutant Spider and hauled the platform up again and by the time it got to the top, it picked up 25 more aircraft for a total of 75.

I’m not quite sure what the deal is. I’ll post some pics of the platform and antenna mounts in another thread so you can see that changing out the two antennas involved only replacing the antenna itself. No cables were even reconnected. I suspect it has something to do with the strong RF field from the TV and FM transmitters but I’ll have to test more.

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What does it look like when you sweep it from the bottom of the longer cable as opposed to when you sweep it at the antenna itself?

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Sounds like it is also a good antenna for [random interfering transmitter here]. Wideband SDRs don’t deal with strong out of band interference too well.

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Can you please run RF scan of your V-Lad while it is up on the platform?

Scan method given in the thread Do I Need A Filter?