It is currently Wed Jul 15, 2020 10:58 am

Click the link below to visit the site sponsor

The Ham Radio Shop




Post new topic Reply to topic  [ 8 posts ] 
 Coaxial collinear help please... 
Advanced Member
User avatar

Joined: Wed Jan 30, 2013 2:44 am
Posts: 881
Location: Nottingham
Feedback: 8 (100%)
Reply with quote
Post 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 !

_________________
73

Paul


Sat Apr 11, 2015 4:46 pm
Profile Send private message

 Coaxial collinear help please... 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post Re: Coaxial collinear help please...
Yes - you need to take account of the velocity factor.

What type of analyser do you have?

Steve G3TXQ

_________________
"I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind;" (Lord Kelvin 1883)


Sat Apr 11, 2015 10:00 pm
Profile Send private message WWW

 Coaxial collinear help please... 
Moderator

Joined: Fri Jul 20, 2007 1:02 pm
Posts: 15099
Location: IO83lb, Wrexham
Feedback: 16 (100%)
Reply with quote
Post Re: Coaxial collinear help please...
Just out of interest, what are you looking at receiving, on 23cm, that's vertically polarised?

Cheers

Tony

_________________
50MHz and above from IO83lb


Sun Apr 12, 2015 8:32 am
Profile Send private message

 Coaxial collinear help please... 
Top Poster
User avatar

Joined: Sat May 23, 2009 1:46 pm
Posts: 20872
Location: Shropshire UK IO82TN
Feedback: 5 (100%)
Reply with quote
Post 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!

_________________
Dave G0BHD.
Been there and got the T shirt, sadly like the T shirt the memory of it has long since faded, gone rather tatty, and finally been consigned to the bin!


Sun Apr 12, 2015 9:11 am
Profile Send private message

 Coaxial collinear help please... 
Moderator

Joined: Fri Jul 20, 2007 1:02 pm
Posts: 15099
Location: IO83lb, Wrexham
Feedback: 16 (100%)
Reply with quote
Post 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

_________________
50MHz and above from IO83lb


Sun Apr 12, 2015 1:55 pm
Profile Send private message

 Coaxial collinear help please... 
Top Poster
User avatar

Joined: Sat May 23, 2009 1:46 pm
Posts: 20872
Location: Shropshire UK IO82TN
Feedback: 5 (100%)
Reply with quote
Post 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:

_________________
Dave G0BHD.
Been there and got the T shirt, sadly like the T shirt the memory of it has long since faded, gone rather tatty, and finally been consigned to the bin!


Sun Apr 12, 2015 2:04 pm
Profile Send private message

 Coaxial collinear help please... 
Advanced Member
User avatar

Joined: Wed Jan 30, 2013 2:44 am
Posts: 881
Location: Nottingham
Feedback: 8 (100%)
Reply with quote
Post 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

_________________
73

Paul


Sun Apr 12, 2015 3:13 pm
Profile Send private message

 Coaxial collinear help please... 
Silent Key

Joined: Fri May 22, 2009 1:23 pm
Posts: 5637
Location: Northampton IO92ME
Feedback: 1 (100%)
Reply with quote
Post 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


Sun Apr 12, 2015 3:36 pm
Profile Send private message WWW
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 8 posts ] 


Who is online

Users browsing this forum: G8NYZ and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB © phpBB Group.
Designed by Vjacheslav Trushkin for Free Forums/DivisionCore.