I'm a bit confused over the construction of a vertical colinear.

The docs I've seen all are more or less the same, alternating half-wave
sections of coax or hardline.
The thing that's bending my head, is that there's a velocity factor inside
the coax, that presumably isn't there on the outside.
So, while a given section is a half wave on the outside, it's probably more
like 3/4 wave inside.

My understanding is that we are trying to get to a series of dipoles all fed
in phase, and yet this seems like it's not accomplishing that.

What am I missing?

"Dave VanHorn" bravely wrote to "All" (02 Oct 05 09:15:26)
--- on the heady topic of "Vertical colinear"

DV From: "Dave VanHorn"
DV Xref: core-easynews rec.radio.amateur.antenna:217909

DV I'm a bit confused over the construction of a vertical colinear.

DV The docs I've seen all are more or less the same, alternating
DV half-wave sections of coax or hardline.
DV The thing that's bending my head, is that there's a velocity factor
DV inside the coax, that presumably isn't there on the outside.

DV So, while a given section is a half wave on the outside, it's probably
DV more like 3/4 wave inside.
DV My understanding is that we are trying to get to a series of dipoles
DV all fed in phase, and yet this seems like it's not accomplishing that.

DV What am I missing?


The wave energy travels alternately on the outside of the center
conductor and then on the inside of the braid or shielding. So both
see the same velocity factor. Does that make sense?

A*s*i*m*o*v

.... What if there were no hypothetical situations?

The wave energy travels alternately on the outside of the center
conductor and then on the inside of the braid or shielding. So both
see the same velocity factor. Does that make sense?

Hmm..
So the first and second radiators are not in phase, but the first, third,
fifth .... are in phase with each other, and the second, fourth, etc are in
phase with each other?

"Dave VanHorn" wrote in message
...
I'm a bit confused over the construction of a vertical colinear.

The docs I've seen all are more or less the same, alternating half-wave
sections of coax or hardline.
The thing that's bending my head, is that there's a velocity factor inside
the coax, that presumably isn't there on the outside.
So, while a given section is a half wave on the outside, it's probably
more like 3/4 wave inside.

My understanding is that we are trying to get to a series of dipoles all
fed in phase, and yet this seems like it's not accomplishing that.

What am I missing?

Hi dave

I dont think you are missing anything. The feed points of each of the
radiating elements need to be in phase if 'broadside pattern max' is
desired.

Do you intend to build an array, or just trying to understand them?

Jerry

I dont think you are missing anything. The feed points of each of the
radiating elements need to be in phase if 'broadside pattern max' is
desired.

Do you intend to build an array, or just trying to understand them?


Both. I have some FSJ1-50 that I got for the purpose.

The docs that I've seen are all pretty consistent on how it should be put
together, but I just don't understand the workings of it.

IF the coax had a VF of 1.0, then it would make sense to me.

Do all the elements radiate?

"Dave VanHorn" wrote in message
...

I dont think you are missing anything. The feed points of each of the
radiating elements need to be in phase if 'broadside pattern max' is
desired.

Do you intend to build an array, or just trying to understand them?


Both. I have some FSJ1-50 that I got for the purpose.

The docs that I've seen are all pretty consistent on how it should be put
together, but I just don't understand the workings of it.

IF the coax had a VF of 1.0, then it would make sense to me.

Dave

Have you looked at the collinear antenna on the web written by "Brian
Oblivious"? He cuts the coax into equal lengths 1/2 wave each. And that
1/2 wavelength accounts for the velocity of propagation inside the coax.
So, each length is somewhat shorter than the free space halfwave It shows
how he connected lengths of coax to make a collinear array. In my opinion,
that would be a waste of that good coax you have.

I once manufactured a vertical collinear antenna that had only one feed
point and the other collinear elements were passively connected when stacked
below the "fed dipole".

Sometimes it is convenient to mount vertical half wave dipoles around a
vertical supporting mast and have a "corporate feed harness" within the
mast. That works well.

Have you looked at the collinear antenna on the web written by "Brian

Oblivious"?

No, I googled on it but didn't hit anything.

He cuts the coax into equal lengths 1/2 wave each.

The articles I have seen are 1/2 wave * the velocity factor.

Each one connecting center to shield.

I can't picture how the elements all end up resonant, and in phase.

Seems like one of those can't be true.

And that

1/2 wavelength accounts for the velocity of propagation inside the coax.

So, each length is somewhat shorter than the free space halfwave It shows

how he connected lengths of coax to make a collinear array. In my opinion,

that would be a waste of that good coax you have.

Why? It's nice rigid coax, and takes that sort of soldering well.

"Dave VanHorn" wrote in message
...
Have you looked at the collinear antenna on the web written by "Brian

Oblivious"?

No, I googled on it but didn't hit anything.

He cuts the coax into equal lengths 1/2 wave each.

The articles I have seen are 1/2 wave * the velocity factor.

Each one connecting center to shield.

I can't picture how the elements all end up resonant, and in phase.

Seems like one of those can't be true.

And that

1/2 wavelength accounts for the velocity of propagation inside the coax.

So, each length is somewhat shorter than the free space halfwave It shows

how he connected lengths of coax to make a collinear array. In my
opinion,

that would be a waste of that good coax you have.

Why? It's nice rigid coax, and takes that sort of soldering well.


Dave

I didnt mean to imply that your good coax wouldnt work well. I (perhaps
wrongly) assumed that some garden variety coax might work OK for that
staggering of lengths of coax, inner conductor to outer conductor.

My web service thru Google, gets me that Brian Oblivious + Capt Kaboom
site on their 802.11 2.4 GHz antenna. They indicate that the "elements" are
1/2 wave long minus the Vp inside the coax. That will put the feed points
along that 'staggered' array, in phase.

You have probably already considered that there will be some beam squint
with this type of collinear. The "corporate fed" collinear will a
maintain a main beam broadside, even though sidelobes do increase with
bandwidth.

Jerry