True widenhof true. I’ll be honest when i was trying these out i had them in the attic space of my house so they didnt need a housing
Oliver Jowett (@obj) succeeded in making a very good one couple of years ago
And the most critical one (VF) is almost impossible to find for readily available coax. One has to purchase coax from those sellers who provide the data sheet.
The PE (PolyEtylene) insulated coax has a fixed VF=0.66 irrespective of manufacturer.
The PTFE (PolyTetraFluoroEthylene) insulated coax has a fixed VF=0.69 irrespective of manufacturer.
Satellite TV coax is FPE (Foamed PolyEthylene) insulated. The FPE does not have a fixed VF. It’s VF depends on degree of foaming done during manufacture of the coax.
- More the air/gas used to create foaming, closer the VF to 1.
- More the foaming, softer the insulation, and cable is more flexible.
- More foaming means less PolyEthylene used per meter run, reducing the cost.
Although good manufacturers use a degree of foaming which gives VF around 0.83 ~ 0.85, lot of manufacturer making Satellite coax use much more/less foaming. As a result low cost Satellite TV RG6 available easily everywhere may have VF of any value from say 0.8 to 0.9
This peculiar nature of the most abundant and cost-effective coax worldwide makes it unsuitable for making a Coco.
Some people think that Satellite coax RG6 is inferior. This is wrong concept as RG6 is designed for GHz frequencies. The attenuation/meter is higher than LMR, but Coco being only about a meter long, it is insignificant.
The real problem in using Satellite coax for making a Coco is its very wide and unspecified VF due to large variations in foaming from manufacturer to manufacturer.
I don’t think you are presenting a meaningful argument.
It doesn’t matter matter what you want to do, be it: grow orchids, race go-carts, tie fishing flys, photography, embroidery etc. every hobby has an entry level and a path for improvement. If you can’t be bothered learning to improve you skills, you don’t improve. Research what is important and what is not is part of the development process.
This is simply a matter of well written advice / instructions and is just as important as any dimension.
With an internet connection or even a phone book, anyone capable of finding this site could also find a cable supplier.
I don’t see the difference between importing a ready-made antenna vs. the components to build one.
That certainly appears to be true, but anyone building a CoCo, is after a “better” antenna (maybe as little as 3dB better, maybe more - constructors choice).
If you only want the performance of a 1/4 wave, build that.
Didn’t some guy say:
“We do these things, not because they are easy, but because they are hard”?
It’s the rewards we are after.
Your approach is right that if someone wants to build a good Coco, he can easily do it by spending some money to purchase a piece of coax from a reputable source which has data sheet available, and then excersise accuracy in cuting and assembling the elements.
If my objective was also to make a good Coco for myself, I could have done it years ago as I can easily find a supplier of good coax of known VF on line, can easily afford to pay the cost of cable, shipment and duty, and I have enough technical knowledge and skill to built a good Coco easily.
But I did not do it. Why? Because my objective never was to build a good Coco for myself. My objective always was to build a “Poor Man’s Coco” which can be build almost everywhere in the world without need for special coax, which may be unavailable and/or unaffordable to most in the world.
I think because our objectives are poles apart, we can never reach a concensus. It is better not to waste our time in this debate.
When dust settles a bit here at home I will try to repeat my build with other coax
… and with different supplier.
Both reasonably priced with shipping in US. Any advise for other coax for less that $15 (including shipping) will be considered.
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.
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.
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).
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.
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.
I have created a new thread dedicated to CoCo. You may please post about CoCo there. Thank you.
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.
Is COCO Your Cup of Tea?
By L.B. Cebik, W4RNL
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.