20 meter J antenna
 

For A while now I have been pondering practical ways to build a 20 meter J
antenna mostly for the grins and giggles of doing it. Recently I came by a
couple of lengths of triangluklar tower. I was thinkinking about erecting
these an placing a metal pole down the middle shorting the two together at
about 16 ft from the top. The radiator would consist of a 30+ ft fiberglass
whip. Any thoughts on this design would be appreciated. Other ideas for a J
have been dismissed because they would require guys. I need something that
would be freestanding.

Why use a J at all? I'd just use a 1/2 wave radiator,
and feed it using a gamma loop setup. ,For 20m,
a 20 inch single turn loop should work ok. Can be
made from copper, or aluminum tubing. If you need
a capacitor, it can be made from coax. For 20m, about
100-140 pf should be pretty close... BTW.. this design
would be the same as any VHF ringo...MK

Jimmie wrote:
I need something that would be freestanding.

50 foot tall free-standing things are mighty expensive.
Even more so since the bottom 16.5 feet must be
designed not to radiate.
--
73, Cecil http://www.qsl.net/w5dxp

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Jimmie:

A half-wave radiator (the J is such) is an excellent ant and it can be run
without ground plane...

However, the J with the added bulk of the quarter-wave matching section
makes no sense, when a gamma match can be used with a slight gain in
efficiency... I worked out such a design and use it on 10 meters... a 1:1
current balun at the ant is necessary, or ferrite beads over the shield of
the coax--I found an inductive reactance of the balun/beads of about 2000
ohms at the operating freq is ideal and halts all line currents.... the
lenght of the gamma rod will be approx. 1/3 longer when used on a 1/2 wave
then when used on a 1/4.... I use no counterpoise, but a 1/4 lenght of wire
can be hooked at ground and the ant worked against it... I find it
unnecessary with the balun and ant properly tuned and matched...

You will not see this ant on the web... take my word for it, it is a decent
antenna... better yet, try it, if you are unhappy, just remove the gamma
and stick on the 1/4 wave matching section and you have the J...

Warmest regards,
John

"Jimmie" wrote in message
. com...
For A while now I have been pondering practical ways to build a 20 meter J
antenna mostly for the grins and giggles of doing it. Recently I came by a
couple of lengths of triangluklar tower. I was thinkinking about erecting
these an placing a metal pole down the middle shorting the two together at
about 16 ft from the top. The radiator would consist of a 30+ ft
fiberglass whip. Any thoughts on this design would be appreciated. Other
ideas for a J have been dismissed because they would require guys. I need
something that would be freestanding.

Well, I said that wrong, I figure the length of the gamma rod will run right
around 6 ft for 20 meters, this should get you close enough to tune from,
the cap reactance needed in series with the rod will need to be of a value
to cancel that of the inductive reactance intoduced by the gamma rod... I
think that is clearer...

Warmest regards,
John

"John Smith" wrote in message
...
Jimmie:

A half-wave radiator (the J is such) is an excellent ant and it can be run
without ground plane...

However, the J with the added bulk of the quarter-wave matching section
makes no sense, when a gamma match can be used with a slight gain in
efficiency... I worked out such a design and use it on 10 meters... a
1:1 current balun at the ant is necessary, or ferrite beads over the
shield of the coax--I found an inductive reactance of the balun/beads of
about 2000 ohms at the operating freq is ideal and halts all line
currents.... the lenght of the gamma rod will be approx. 1/3 longer when
used on a 1/2 wave then when used on a 1/4.... I use no counterpoise, but
a 1/4 lenght of wire can be hooked at ground and the ant worked against
it... I find it unnecessary with the balun and ant properly tuned and
matched...

You will not see this ant on the web... take my word for it, it is a
decent antenna... better yet, try it, if you are unhappy, just remove the
gamma and stick on the 1/4 wave matching section and you have the J...

Warmest regards,
John

"Jimmie" wrote in message
. com...
For A while now I have been pondering practical ways to build a 20 meter
J antenna mostly for the grins and giggles of doing it. Recently I came
by a couple of lengths of triangluklar tower. I was thinkinking about
erecting these an placing a metal pole down the middle shorting the two
together at about 16 ft from the top. The radiator would consist of a 30+
ft fiberglass whip. Any thoughts on this design would be appreciated.
Other ideas for a J have been dismissed because they would require guys.
I need something that would be freestanding.

John Smith wrote:


I worked out such a design and use it on 10 meters...

28 MHz, or 28 MHz?

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