Problem with self made CoCo


#1

Hey guys,
I started feeding a few weeks ago with a little ready to use adsb antenna having semi good results. For that reason, I decided to build a coaxial collinear antenna myself based on the tutorial on https://www.balarad.net/. I read the “Three Easy DIY Antennas for Beginners” thread in the forum, however a coco is the most suitable choice for my installation location. Otherwise I would have to purchase the official Flightaware antenna, but I would prefer the budget option.
After assembling the antenna out of 8 pieces of RG6U cable I was unsure how to connect the antenna to my receiver (I am using the flightaware pro stick plus). I tried to take an additional 9th cable element (approx 1ft long) as feed line, connected to the antenna the way you connect the antenna segments themselves together on the first site. On the other side, I took a SMA connector like this and installed it using the center of the coaxial cable as the pin of the SMA connector. Unfortunately, I only receive one or two aircrafts or even nothing at all, while receiving about 10 planes with the cheap ready to use antenna. I never worked with coaxial cables nor SMA connectors before, I actually think the issue is about this connector installation. I searched the internet for other tutorials of the CoCo where they explain how to install a SMA connector but I couldnt find one. Does anyone have a hint for me?
Thanks in advance!


#2

The connector you have used is for RG174 cable which is much thinner than RG6U. This possibly has caused a broken connection.

The title of connector says:
SMA-Steckverbinder Stecker, gerade 50 Ω Conrad Components SMA-JC-RG174-1 1 St

Better fix a F-male connector to RG6U cable, and use a “F-female to SMA-male pig tail” to connect RG6U to the Dongle

An example from ebay.de is here


#3

@thberlin
i used also a coco based on the instructions from that site.
8 elements and feeder line 2m, no resistor termination and no stub
or power, and an adapter F-female to sma male.
not bad results, and the antenna on top of a high building.
not as good as the cantenna though.
however as abcd567 points out in different posts, cocos are very
difficult to ‘trim’ and get it right, if you haven’t got the equipment !
a mere multi-tester is not enough.
so i reverted back to the cantenna with the top instead of
wire, a piece of copper tube 6.8cm and the result is day/night.

HTH
Evangel


#4

Have a look at this post of thread “Improving my coco antenna”.

You may like to also see other posts of this thread (now 2 pages).

https://forum.flightradar24.com/threads/11711-Improving-my-coco-antenna?p=102713&viewfull=1#post102713

.


#5

You have several problems.
First, I suggest you stick to 50 Ohm coax, stay away from cheap TV coax.
Get a length of LMR400 (thick) or RG58 (thin), if you have more than 10 ft of coax then go LMR 400 or similar.

Order your coax with N connectors on both ends, this way you can use chassis mount female N connectors for the supply point of your home brew antenna or commercial antenna.

Use a converter to go from N connector to SMA.
Next get some pigtales , short cables with what ever connectors you need,
say SMA male to SMA male to go from your amplifier to your filter or amplifier to your USB dongle.

USE LMR 400 for your co-axial colinear elements, keep the gap between elements as short as possible.

If you want to stay SMA then get SMA chassis connectors , stay away from F connectors.
I’ve got a box full of them and only use them for 1090 if I’m desperate.

If you got to excessive number of elements it will become very narrow in bandwidth to the point that it will not cover the entire band, or, you make mistakes with measurement and end up with an antenna that is not at the center frequency, and start losing lower signal strengths.

Stick to around 4 elements till you get it working the first time with better signals.

The only antenna you can really trust is the antenna you make yourself absent buying commercially rated antennas as sold by Flight Aware etc.

The reliable first antennas are

  1. 88 mm of copper poking out a bit of coax.
  2. 88mm of copper poking out with 88 mm of shield forming a Sleeve on the coax.
  3. 88 mm of copper poking out with 45 degree ground plane elements
  4. 88 mm dipoles out of the top of a can.

Now the measurement for 2mm to 12.4 mm copper elements is 88.9 mm
to one decimal place.

The thicker the copper element the broader the bandwidth and the easier it is to get that measurement exact, not that 1mm is going to make much difference on a can antenna, but
its good practice for when you go to a larger number of elements.

A digital micrometer then becomes a necessity for construction.

As pointed out by other posters, its important to have several antennas made and use one as your Datum reference point by which to judge the others.

“how to install connectors”
First you need a CRIMPING TOOL,

You must really go to the ebay seller n5iaw
who is an extremely supportive Amateur Radio operator who sells
Crimping tools and dies. Here is a link.


I have known this seller for many years
and it is an incredible nice gentleman who goes beyond the call of duty and that is
still an understatement. He deserves a plug so here are some links.


#6

Thanks for all your great input!

I actually saw this SMA connector is made for RG174 when I puchased it but it was the only one i found at the store so I bought it hoping it will work out. Bad luck.

Unfortunately I do not have any crimping equipment - I would like buying the one you suggested, however its even more expensive than just buying the official flightaware antenna, due to shipping and customs costs (I am based in germany). I will ask a few friends, maybe I find someone who can borrow me his one for a few. And I will check for cables that are already equipped with a N connector, so I could avoid installing connectors on my own.


#7

Check out www.jetvision.de for products local to Germany.
They sell quality products.
I have bought their mode S Beast, cavity filters and radarcape.