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Old October 11th 03, 07:03 PM
Serge Stroobandt, ON4BAA
 
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Default QST Article: An Easy to Build, Dual-Band Collinear Antenna

Dear OMs,

Via this newsgroup I learned that last September the following article
appeared in QST:

p.28: An Easy to Build, Dual-Band Collinear Antenna by Dan Friedrichs,
K0IPG

I am particularly interested in this article, because at this very moment I
am designing myself a 70cm colinear.
Unfortunately, I do not have access here to this article.

Before I contact the ARRL's reprint service, I was wondering if somebody of
this newsgroup who has read this article,
could brievely describe the basis principle of this antenna (coils?, phased
line?, electrical length?).

Many thanks!

73 de Serge ON4BAA / HB9DWU
http://salsawaves.com/propagation/



  #2   Report Post  
Old October 12th 03, 04:20 AM
Crazy George
 
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Well, Serge,

It consists of 5 major parts. A piece of 300 ohm twinlead, a coil, some
wire, a copper disk plus a length of PVC pipe and cap on top. The twinlead
matches 50 ohm input to the radiator, which consists of two half waves on 2M
separated by a phasing coil. On 70 CM, the radiator will be two full
wavelength radiators in phase.

Matching section:
Start with a piece of 300 ohm twinlead about 50 cm long. Strip and short
one end. 3.8 cm from the short, remove a few mm of insulation from both
conductors, and connect a 50 ohm coax to it, center conductor to one side
(call it A) and shield to the other side. Now, trim the twinlead to exactly
42.4 CM long, leaving this end open. Remove 1.3 cm of insulation from the
conductor on the A side. This is where the radiator will attach.

Phasing coil:
Dry wood dowel (or Plexiglas or polystyrene, but not PVC) 1.3 cm diameter
(actually 1/2") and 3.8 cm (1.5") long. Drill a 2.5 or 3 mm hole through
each end to hold the ends of a coil. You need about 55 cm of solid 20 gage
(0.889 mm dia.) insulated wire. Wind 13 equally spaced turns of this 20
gage wire on the dowel and pass the ends through the holes. Cut the ends
leaving a couple of cm on each end. Strip a cm of insulation off each end.
These dimensions are likely to be fairly critical.

Radiator:
Made from straight pieces of 12 gage (2.053 mm) insulated solid wire.
(Typical house wiring material in the US.) Cut one piece 97.8 cm long,
strip a few mm of insulation from each end, and connect (solder) from A of
the twin lead to one end of the coil. Cut a second piece the same (97.8 cm)
length, and solder to the other end of the coil. The wire diameter is not
critical, but the lengths are.

Pipe and top disk:
The author used a 10 foot (3.1 M) piece of 3/4" (nominal OD ~ 27 cm) PVC
pipe to support this assembly. He cut a piece of copper clad material just
larger than the ID of the pipe, drilled a hole in the center and passed the
end of the second piece of 12 gage wire through it and soldered it. Then he
dropped the antenna in the pipe, and put a PVC pipe cap over the end.

The author recommends adjusting the lengths of the twin lead and the
radiator wires to achieve best SWR.
--
Crazy George
Remove NO and SPAM from return address
"Serge Stroobandt, ON4BAA" wrote in message
...
Dear OMs,

Via this newsgroup I learned that last September the following article
appeared in QST:

p.28: An Easy to Build, Dual-Band Collinear Antenna by Dan Friedrichs,
K0IPG

I am particularly interested in this article, because at this very moment

I
am designing myself a 70cm colinear.
Unfortunately, I do not have access here to this article.

Before I contact the ARRL's reprint service, I was wondering if somebody

of
this newsgroup who has read this article,
could brievely describe the basis principle of this antenna (coils?,

phased
line?, electrical length?).

Many thanks!

73 de Serge ON4BAA / HB9DWU
http://salsawaves.com/propagation/




  #3   Report Post  
Old October 12th 03, 06:24 AM
Richard Clark
 
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On Sat, 11 Oct 2003 22:20:19 -0500, "Crazy George"
wrote:

On 70 CM, the radiator will be two full
wavelength radiators in phase.


Hi George,

Hardly sounds very useful except for working satellites or
mountain-top repeaters if you live in a valley.

73's
Richard Clark, KB7QHC
  #4   Report Post  
Old October 12th 03, 09:58 AM
Serge Stroobandt, ON4BAA
 
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Dear George,

Thank you for having taken the time to answer me in such detail.
This is very kind of you.

73 de Serge ON4BAA / HB9DWU
http://salsawaves.com/propagation/


"Crazy George" wrote in message
...
Well, Serge,

It consists of 5 major parts. A piece of 300 ohm twinlead, a coil, some
wire, a copper disk plus a length of PVC pipe and cap on top. The

twinlead
matches 50 ohm input to the radiator, which consists of two half waves on

2M
separated by a phasing coil. On 70 CM, the radiator will be two full
wavelength radiators in phase.

Matching section:
Start with a piece of 300 ohm twinlead about 50 cm long. Strip and short
one end. 3.8 cm from the short, remove a few mm of insulation from both
conductors, and connect a 50 ohm coax to it, center conductor to one side
(call it A) and shield to the other side. Now, trim the twinlead to

exactly
42.4 CM long, leaving this end open. Remove 1.3 cm of insulation from the
conductor on the A side. This is where the radiator will attach.

Phasing coil:
Dry wood dowel (or Plexiglas or polystyrene, but not PVC) 1.3 cm diameter
(actually 1/2") and 3.8 cm (1.5") long. Drill a 2.5 or 3 mm hole through
each end to hold the ends of a coil. You need about 55 cm of solid 20

gage
(0.889 mm dia.) insulated wire. Wind 13 equally spaced turns of this 20
gage wire on the dowel and pass the ends through the holes. Cut the ends
leaving a couple of cm on each end. Strip a cm of insulation off each

end.
These dimensions are likely to be fairly critical.

Radiator:
Made from straight pieces of 12 gage (2.053 mm) insulated solid wire.
(Typical house wiring material in the US.) Cut one piece 97.8 cm long,
strip a few mm of insulation from each end, and connect (solder) from A of
the twin lead to one end of the coil. Cut a second piece the same (97.8

cm)
length, and solder to the other end of the coil. The wire diameter is not
critical, but the lengths are.

Pipe and top disk:
The author used a 10 foot (3.1 M) piece of 3/4" (nominal OD ~ 27 cm) PVC
pipe to support this assembly. He cut a piece of copper clad material

just
larger than the ID of the pipe, drilled a hole in the center and passed

the
end of the second piece of 12 gage wire through it and soldered it. Then

he
dropped the antenna in the pipe, and put a PVC pipe cap over the end.

The author recommends adjusting the lengths of the twin lead and the
radiator wires to achieve best SWR.
--
Crazy George
Remove NO and SPAM from return address
"Serge Stroobandt, ON4BAA" wrote in

message
...
Dear OMs,

Via this newsgroup I learned that last September the following article
appeared in QST:

p.28: An Easy to Build, Dual-Band Collinear Antenna by Dan Friedrichs,
K0IPG

I am particularly interested in this article, because at this very

moment
I
am designing myself a 70cm colinear.
Unfortunately, I do not have access here to this article.

Before I contact the ARRL's reprint service, I was wondering if somebody

of
this newsgroup who has read this article,
could brievely describe the basis principle of this antenna (coils?,

phased
line?, electrical length?).

Many thanks!

73 de Serge ON4BAA / HB9DWU
http://salsawaves.com/propagation/






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Old October 13th 03, 04:16 AM
Crazy George
 
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I agree. Which is why I mentioned it. You should discuss it with the
author of the article. I was just trying to do a favor for someone "over
there".

--
Crazy George
Remove NO and SPAM from return address
"Richard Clark" wrote in message
...
On Sat, 11 Oct 2003 22:20:19 -0500, "Crazy George"
wrote:

On 70 CM, the radiator will be two full
wavelength radiators in phase.


Hi George,

Hardly sounds very useful except for working satellites or
mountain-top repeaters if you live in a valley.

73's
Richard Clark, KB7QHC





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Old October 13th 03, 04:41 AM
Cecil Moore
 
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Crazy George wrote:
I agree. Which is why I mentioned it. You should discuss it with the
author of the article. I was just trying to do a favor for someone "over
there".


EZNEC sez that two vertical dipoles stacked end to end have a gain of
about 3dBi with their sources in phase at their centers. I'm sure you
have seen the UHF folded dipole vertical stacked arrays.
--
73, Cecil http://www.qsl.net/w5dxp



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  #7   Report Post  
Old October 13th 03, 11:23 PM
Serge Stroobandt, ON4BAA
 
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That is absolutely correct, Cecil.

I am currently designing a 70cm colinear with two 5/8 elements, fed in the
middle over a stub with balun
and made entirely out of standard (in Europe) 12mm diameter copper tubing.

AO (Antenna Optimizer) predicts a gain of 3.3dBi in free space.
Due to the stub the pattern is not entirely uniform and therefore in one
direction I would have a bit more gain upto 5dBi according to AO.

In the coming weeks (sorry, but I have a demanding job and a HF antenna
project that takes presidence) I will model the antenna also in EZNEC
to double-check its matching to 50ohm and than build it.

Of course I will share the results and final measure in this newsgroup.

I had asked for the QST design in this group, simply to see if I could
improve on my design but it does not seem so.

Thanks guys for your help and Cecil, intersting stuff on your website!

73 de Serge ON4BAA / HB9DWU
http://salsawaves.com/propagation/


"Cecil Moore" wrote in message
...
Crazy George wrote:
I agree. Which is why I mentioned it. You should discuss it with the
author of the article. I was just trying to do a favor for someone

"over
there".


EZNEC sez that two vertical dipoles stacked end to end have a gain of
about 3dBi with their sources in phase at their centers. I'm sure you
have seen the UHF folded dipole vertical stacked arrays.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
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  #8   Report Post  
Old October 14th 03, 01:23 AM
Art Unwin KB9MZ
 
Posts: n/a
Default

Cecil Moore wrote in message ...
Crazy George wrote:
I agree. Which is why I mentioned it. You should discuss it with the
author of the article. I was just trying to do a favor for someone "over
there".


EZNEC sez that two vertical dipoles stacked end to end have a gain of
about 3dBi with their sources in phase at their centers. I'm sure you
have seen the UHF folded dipole vertical stacked arrays.


Cecil
I used stacked vert dipoles and 12 watts for two meters
when my son was in hospital a 100 miles away and we used
a repeater nearby so he could use a H.T. I don.t remember
seeing a MOUNTAIN here in Central Illinois and other
antennas couldn't reach it

I do like the dipole overlay on the vertical pattern on your
page.Actualy I enjoyed the whole page
Makes you wonder why all people don't use horizontal
polarisation to get away from ground losses.
The pattern looks just like the one I generated for a dipole
over a beverage for the top band using AO Pro and just goes
to show that max radiation at a high angle in not always bad.
( That comment will attract a few people to your page! )
Regards
Art
Regards
Art
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Old October 14th 03, 02:56 AM
Serge Stroobandt, ON4BAA
 
Posts: n/a
Default


"Art Unwin KB9MZ" wrote in message
m...
Cecil Moore wrote in message

...

Cecil


I do like the dipole overlay on the vertical pattern on your
page.Actualy I enjoyed the whole page
Makes you wonder why all people don't use horizontal
polarisation to get away from ground losses.


This conversation is starting to get interesting :-)

INVERTED GROUNDPLANES:
What about using an inverted 1/4wave groundplane in order to avoid ground
losses?
Then you have the high impedance point of the antenna close to the lossy
(low impedance) earth.
Due to the severe mismatch less power will couple into the earth.

The low impedance point (feed point) of the antenna is safely high up in the
(high impedance) air then.


--

73 de Serge ON4BAA - HB9DWU
http://salsawaves.com/propagation/


  #10   Report Post  
Old October 14th 03, 03:13 AM
Roy Lewallen
 
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That question has been answered several times in this newsgroup. For one
of the most recent answers, go to groups.google.com and find my posting
on July 21, 2003 in the thread " efficiency of horizontal vs vertical
antennas".

Roy Lewallen, W7EL

Serge Stroobandt, ON4BAA wrote:

This conversation is starting to get interesting :-)

INVERTED GROUNDPLANES:
What about using an inverted 1/4wave groundplane in order to avoid ground
losses?
Then you have the high impedance point of the antenna close to the lossy
(low impedance) earth.
Due to the severe mismatch less power will couple into the earth.

The low impedance point (feed point) of the antenna is safely high up in the
(high impedance) air then.





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