Colinear question
 

As I understand it,a colinear antenna, is a series of half wave
elements, that are phase reversed (if that make sense) from one to the
next.

Could you build a colinear of a single long line, bending it outa nd
back, at 90deg, every half wave, with the bit sticking out (and back)
being a half wave total out and back? would that result in the same
effect as a colinear?

something like this.

Feed __||__||__||__



--
Jim Richardson http://www.eskimo.com/~warlock
Televangelists: The Pro Wrestlers of Religion

Yep!! VArious version of 'Curtains' use the technique. The Sterba
Curtain comes to mind.

Jim Richardson wrote:
As I understand it,a colinear antenna, is a series of half wave
elements, that are phase reversed (if that make sense) from one to the
next.

Could you build a colinear of a single long line, bending it outa nd
back, at 90deg, every half wave, with the bit sticking out (and back)
being a half wave total out and back? would that result in the same
effect as a colinear?

something like this.

Feed __||__||__||__

Yes!

The "there and back" is often seen as phasing coils on mobile UHF
verticals. Also the same kind of logic as a colinear J pole (for
example) that has the hairpin shaped thing about half way up the
radiating section of the antenna.

You can also get colinear effects by using alternate halfwaves of very
thick vs very thing elements (eg 25mm pipe and 2mm wire on 144MHz) but
as one long "element" rather than bending it back and forth. (Yes the
gain is lower for a given length)

Keep in mind that it is prudent to feed in the middle of the antenna,
probably at one of the hairpins sections. Its a good place as somewhere
along the phasing section the Z will be that of your feedline. If you
feed at the end the pattern tends to skew away from the feedpoint.

Cheers Bob VK2YQA

Jim Richardson wrote:
....

something like this.

Feed __||__||__||__

I cannot back it up with numbers but as I recall (with a fixed number
of elements) better results were achieved with a phasing harness. I
have always suspected that the elements closer to the source were
contributing the most. It sounds like a question that might be easily
answered by modeling.

On Mon, 03 Oct 2005 09:19:57 -0400, Amos Keag
wrote:

Yep!! VArious version of 'Curtains' use the technique. The Sterba
Curtain comes to mind.

Jim Richardson wrote:
As I understand it,a colinear antenna, is a series of half wave
elements, that are phase reversed (if that make sense) from one to the
next.

Could you build a colinear of a single long line, bending it outa nd
back, at 90deg, every half wave, with the bit sticking out (and back)
being a half wave total out and back? would that result in the same
effect as a colinear?

something like this.

Feed __||__||__||__

Jim Richardson wrote:
"Could you build a colinear of a single long line bending it back at 90
deg. every half wave---?"

See the "Super J" in the "ARRL Antenna Book", page 16-25 in my 19th
edition. That is more or less how it is made. The two 1/2-waves,
in-phase, are end-driven with phase inversion provided by a
short-circuited 1/4-wave stub between them.

At frequencies higher than 2-meters, this would work for more than (2)
1/2-wave sections. The practical limitation is mechanical.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Jim Richardson wrote:
"Could you build a colinear of a single long line bending it back at 90
deg. every half wave---?"

See the "Super J" in the "ARRL Antenna Book", page 16-25 in my 19th
edition. That is more or less how it is made. The two 1/2-waves,
in-phase, are end-driven with phase inversion provided by a
short-circuited 1/4-wave stub between them.

At frequencies higher than 2-meters, this would work for more than (2)
1/2-wave sections. The practical limitation is mechanical.

Best regards, Richard Harrison, KB5WZI


Hi Richard

About 45 years ago, I designed a vertical collinear array of dipoles for
1.7 GHz (actually 1,700 Megacycles then). That antenna was a series 1/2
wave sleaves located below a coaxial dipole. The nice aspect was the
simplicty of its feed. The "beam squint got fairly great since there were
alot of passively excited 1/2 wave elements
I had capability of measuring the radiation patterns from the antenna, so
I can assure that the concept you propose will work.

Jerry

On Mon, 03 Oct 2005 09:11:37 -0500,
Bob Bob wrote:
Yes!

The "there and back" is often seen as phasing coils on mobile UHF
verticals. Also the same kind of logic as a colinear J pole (for
example) that has the hairpin shaped thing about half way up the
radiating section of the antenna.

You can also get colinear effects by using alternate halfwaves of very
thick vs very thing elements (eg 25mm pipe and 2mm wire on 144MHz) but
as one long "element" rather than bending it back and forth. (Yes the
gain is lower for a given length)

Keep in mind that it is prudent to feed in the middle of the antenna,
probably at one of the hairpins sections. Its a good place as somewhere
along the phasing section the Z will be that of your feedline. If you
feed at the end the pattern tends to skew away from the feedpoint.

Cheers Bob VK2YQA

Jim Richardson wrote:
...

something like this.

Feed __||__||__||__


Very enlightening responces, thanks all. I have access to a nice HP
vector NA at work, and plan on building a couple of VHF antennas for the
boat (marine band, so centered around 159MHz). The colinear was one I
was considering, "just because". Primary is going to be a copper pipe
j-pole.

--
Jim Richardson http://www.eskimo.com/~warlock
I have plenty of talent and vision. I just don't give a
damn.

On Mon, 3 Oct 2005 11:09:41 -0500,
Richard Harrison wrote:
Jim Richardson wrote:
"Could you build a colinear of a single long line bending it back at 90
deg. every half wave---?"

See the "Super J" in the "ARRL Antenna Book", page 16-25 in my 19th
edition. That is more or less how it is made. The two 1/2-waves,
in-phase, are end-driven with phase inversion provided by a
short-circuited 1/4-wave stub between them.


I just picked up the ARRL book, it's a daunting tome... but interesting
reading.

At frequencies higher than 2-meters, this would work for more than (2)
1/2-wave sections. The practical limitation is mechanical.

Makes sense, thanks.


Best regards, Richard Harrison, KB5WZI


One of these days, hopefully in the near future, I'll get off my ass and
take the ham test. Time.. always about time.

--
Jim Richardson http://www.eskimo.com/~warlock
Unix has security which has been tested by conniving, unscrupulous
college students over generations.

yes

Jim Richardson wrote:

SNIPPED



One of these days, hopefully in the near future, I'll get off my ass and
take the ham test. Time.. always about time.

NAW! It's not about time! It's about priorities!!!!!

There are some things more important than Ham Radio and Antennas. I
suggest GRANDKIDS :-)