Collinear Antenna

[Bounty]

A while ago I saw a construction text for a collinear which I now can't find, although at the time I printed it out.
Unfortunatly the notes and measurements referred to are for a  higher frequency version, well I have done the calculations for 1090 Mhz and would like to check them with someone else before I start the laborious construction.
I hope someone can help.
Regards
Bounty

[nortonbeak]

Was this the article?

http://www.nodomainname.co.uk/Omnicolinear/2-4collinear.htm

[Bounty]

Hi Nortonbeak
Yes this is the article.
I calculated that each section of coax would be 116.9 mm for use with a 1090 Mhz signal for the Airnav box.
What I was after was someone who may have made this to confirm my calculations.

It can't be far off as the frequency is about half that of the article and the elements work out at about double which would be right. The only thing is, is that a mm here or there at these frequencies can be quite important.
I hope that someone can help before I start to build.
Regards
Bounty

[juangelb]

Hi Bounty

Your calculation is right, dont forget that this size is just the half wafelengt and need to observe the details in Mesurements section of the article.
I contructed several antenas with 8, 18 and even 21 dipoles based on this article.
Personally I think that 8 dipoles is enough, but You are right also in take care of any milimeters, since at this wafelenght is very important.
My calculations gave me 9,08 milimeters since I used a 0,66 velocity coax for reducing the oveall lenght of the antenna.
In my case the 8 dipoles one gave me better result than the Wimo.
The 21 dipoles one, I am not sure if due to longer cable run or some error on construction, is not giving me better results than the 8 dipoles one.
Recently I constructed one with 18 dipoles taking extreme care on sizes and I intend to replece the 21 dipoles one with this one, probably this weekend
It is needed to take care also in mantaining the cable run as short as possible and the quality of coax as high as possible due to high losses on it at this frequency.

This antenna model takes some effort to construct it ... for cutting tubes, coax, but I think it worth. The jig also helped a lot on soldering the pieces together.

Fot the fist one it took a lot of time in cutting the tubes, but lather I found a place that sells metals already cutted at the size You want, so this helped me a lot and I saved a lot of time.

Another approach on antennae is one from VK4TEC, very simple and easy to construct and works fine also :
http://www.tech-software.net/1090_antenna.php

OK, go on and good luck

 Juan

[Bounty]

Hi Juan

I am pleased about the fact that my calculations are ok, but you have confused me a bit over the 9.08 mm measurement. Is this the spacing gap or something else?
Regards
Bounty

[juangelb]

hi Bounty

I´M sorry, it is 90,8 mm  an not 9.08 mm

[CoastGuardJon]

Hi Bounty, is there a particular reason for wanting to build a colinear or dipole antenna, other than just for the fun of it, which I fully share?   These antenna tend to be used for directional use rather than omni-directional - they may be able to pick up a/c many miles further out but will exclude others around the lobes.

[juangelb]

Hi CoastGuardJon

Indeed this antenna is a omni-directional and the dipoles are stacked one over other vetically with the purpose of adding sinal strenght from the several dipoles.
The more the dipoles the more the gain.

Cheers.

[Bounty]

Hi Coastguardjon

There are a number of reasons in no particular order

I would like to try an external antenna.
As a radio ham I enjoy the challenge of construction.
And maybe its because I am too mean to buy one, particulaly as I have a fully equipped workshop that I really should try and justify.

Mind you if you have any ideas as to antenna designs thaty I might try I would be pleased to hear of them, as I a new to the Navbox.

Regards
Bounty

[CoastGuardJon]

Hi Juan and Bounty, likewise, I'm very much into homebrew kit, more than fun and satisfaction than boughten black boxes, but so much of today's technology just wouldn't be viable/possible without the microscopically small smds and ics.   Juan, some photos would be appreciated (by others, as well I'm sure) and as they say a picture says a thousand words!   As you are aware, with aerials, the amount of gain shown/claimed by manufacturers is usually very misleading as it normally refers to the mythical Isotropic antenna.   When you see a 3db gain claim, this is 10x the signal strength? or something similar?

[juangelb]

Hi CoastGuardJon

The 3 Dbs gain would be the double the signal, but this is a reference value and You are right that is frequently misleaded or ununderstood.
Even when the 3 dbs would represent the double of the signal, this dos not mean that if with  other antena you receives sinals from, for instance 100 NM that would receive signals from 200 NM with this antenna.
And as shown in the aforemetioned article, I constructes the last one with 18 dipoles that is rated as 9 Db, that would be the double of the double of the double of the signal referenced to a single dipole singnal.
Obviusly the overall range is quite limited to the line of sight and is near 240 NM
in some cases.

About the pictures, OK, I will try to take some and post, but in essence is what appears in the article : a chain of brass tubes with coax core inside and soldered
out of phase. In my case I changed the brass tube for copper tube for my convenience.

The interesting thing is that this project uses a shorted loop, and I did some modification to original project so that the structure of the antenna is gounded.
The idea was to protect RB and SBS-1 from static discharges.

I let all connected all the time no matter what the weather is.
A week or so ago, here was a very strong storm with bolts everywere over my head..... and one bolt hited probably the neighbor building and RB dropped.
I simply disconnected USB cable and connected again... Here we are, all workig fine.
The only time that I disconnect RB or SBS from antenna is for connecting another one antenna for testing, compare and so on.

Cheers

[marcdeklerk]

Can somebody please assist with the exact values for this antenna? I got each element at 137.5mm , the bit above the groundplane at 84.5mm please assist in the groundplane length, and can the groundplane be a round disc of alluminium?

Oh I'll be using lmr400 cable, not sure how the velocity factor will affect the length
Thanks in advance
Marc

[juangelb]

Hi Mark

According to : http://www.rojone.com.au/lmr400_a.pdf
the velocity factor of LMR-400 coax cable is 85%, so You need to use this value in Yout calculation formula.

So the half wafe (using LMR-400) will be : 116,97 mm
You need to dicount the 6 mms from this size ... the same 6 mms that You will be using for spacing between dipoles.
So each brass tube would be of 110,97 mms

Not sure about ground plane.... The original projecto does not include it.

best regards, - Juan