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Coaxial collinear help please...
https://www.hamradiodeals.co.uk/forums/viewtopic.php?f=43&t=65858
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Author:  G0TSG [ Sat Apr 11, 2015 4:46 pm ]
Post subject:  Coaxial collinear help please...

Hi,
I would like to construct a "COCO" for 23cm.

Now, having a pile of 75 Ohm satellite feeder on rolls doing nothing, I thought Id use that (at least for the elements) but its here I'm double guessing myself...

Do we need to take the velocity factor into account - if so I've no idea what it is ! I have an antenna analyser but only goes to 150Mhz.
It will only be used on RX, so would it benefit from a BALUN (assuming its an unbalanced antenna - the net seems to say YES and NO !)
Is there an optimum amount of elements before diminishing returns kicks in ?

Im sure this will need to be mm accurate for best efficiency... so your thoughts please folks !

Author:  G3TXQ [ Sat Apr 11, 2015 10:00 pm ]
Post subject:  Re: Coaxial collinear help please...

Yes - you need to take account of the velocity factor.

What type of analyser do you have?

Steve G3TXQ

Author:  gw8asd [ Sun Apr 12, 2015 8:32 am ]
Post subject:  Re: Coaxial collinear help please...

Just out of interest, what are you looking at receiving, on 23cm, that's vertically polarised?

Cheers

Tony

Author:  G0BHD [ Sun Apr 12, 2015 9:11 am ]
Post subject:  Re: Coaxial collinear help please...

gw8asd wrote:
Just out of interest, what are you looking at receiving, on 23cm, that's vertically polarised?

Cheers

Tony

Fair question, but contrary to popular belief there is some activity on 23 cms FM vertical omni! :D
Round here there are chats from a few locals on FM verticaly polarised, not many I will admit!
There is a small group around the Birmingham area as well that are hearable and workable here, with a simple vertical co-linear!
Also chatting away on FM!
And three guys over in the Black country, that also chat away on vertical FM!
Perhaps as you only work horizontal and SSB or digital modes, you have not heard them?
There was even a repeater up in Stoke on vertical FM, that had reasonable traffic at one time, but I can't hear that anymore, whether thats lack of use or off air, I have not checked!
And one in Featherstone near Wolverhampton, that I believe as also stopped operation!
I will admit though, it is rather thin under foot, not unlike lower UHF/VHF these days!

Author:  gw8asd [ Sun Apr 12, 2015 1:55 pm ]
Post subject:  Re: Coaxial collinear help please...

G0BHD wrote:
gw8asd wrote:
Just out of interest, what are you looking at receiving, on 23cm, that's vertically polarised?

Cheers

Tony

Fair question, but contrary to popular belief there is some activity on 23 cms FM vertical omni! :D
Round here there are chats from a few locals on FM verticaly polarised, not many I will admit!
There is a small group around the Birmingham area as well that are hearable and workable here, with a simple vertical co-linear!
Also chatting away on FM!
And three guys over in the Black country, that also chat away on vertical FM!
Perhaps as you only work horizontal and SSB or digital modes, you have not heard them?
There was even a repeater up in Stoke on vertical FM, that had reasonable traffic at one time, but I can't hear that anymore, whether thats lack of use or off air, I have not checked!
And one in Featherstone near Wolverhampton, that I believe as also stopped operation!
I will admit though, it is rather thin under foot, not unlike lower UHF/VHF these days!

I was just wandering as I'm lead to believe the recommended polarisation for repeaters is horizontal.
Although, on looking, there might be a mixture
I have worked the odd FM station but, likewise, they've always been horizontally polarised, except for the one hand portable.
So it was a genuine question as to what the interest was.

There's some info on coax colinear stack here. http://homepage.ntlworld.com/rossjwilkinson/g6gvi/23cmmobile.html

Cheers

Tony

Author:  G0BHD [ Sun Apr 12, 2015 2:04 pm ]
Post subject:  Re: Coaxial collinear help please...

gw8asd wrote:
G0BHD wrote:
gw8asd wrote:
Just out of interest, what are you looking at receiving, on 23cm, that's vertically polarised?

Cheers

Tony

Fair question, but contrary to popular belief there is some activity on 23 cms FM vertical omni! :D
Round here there are chats from a few locals on FM verticaly polarised, not many I will admit!
There is a small group around the Birmingham area as well that are hearable and workable here, with a simple vertical co-linear!
Also chatting away on FM!
And three guys over in the Black country, that also chat away on vertical FM!
Perhaps as you only work horizontal and SSB or digital modes, you have not heard them?
There was even a repeater up in Stoke on vertical FM, that had reasonable traffic at one time, but I can't hear that anymore, whether thats lack of use or off air, I have not checked!
And one in Featherstone near Wolverhampton, that I believe as also stopped operation!
I will admit though, it is rather thin under foot, not unlike lower UHF/VHF these days!

I was just wandering as I'm lead to believe the recommended polarisation for repeaters is horizontal.
Although, on looking, there might be a mixture
I have worked the odd FM station but, likewise, they've always been horizontally polarised, except for the one hand portable.
So it was a genuine question as to what the interest was.

There's some info on coax colinear stack here. http://homepage.ntlworld.com/rossjwilkinson/g6gvi/23cmmobile.html

Cheers

Tony

All of that is fair comment also Tony, but the ones I can hear and work, (I also only have a vertical up), are using tri band colinears, or other hombrew vertical offerings for their local chat!
One is even on an homebrew co-axial vertical co-linear! (one of the guys over in the Black country)
Repeaters were indeed a mixed batch, I believe the Featherstone one was horizontal, although it was such a good signal here line of sight, I could work it on my Diamond tri band vertical! (until it disappeared!)
Its very fair to say most working 23 cms these days, are employing horizontal antennas of one form or another, and FM isn't the main mode of choice! :good:

Author:  G0TSG [ Sun Apr 12, 2015 3:13 pm ]
Post subject:  Re: Coaxial collinear help please...

G3TXQ wrote:
Yes - you need to take account of the velocity factor.

What type of analyser do you have?

Steve G3TXQ


Its an MFJ 259... HF-2m

Author:  G3TXQ [ Sun Apr 12, 2015 3:36 pm ]
Post subject:  Re: Coaxial collinear help please...

G0TSG wrote:
Its an MFJ 259... HF-2m

In that case, measuring velocity factor should be covered in the manual. In mine it's Section 7.3

Steve G3TXQ

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