I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?
K4WYS

"Sonny Hood" wrote in message
...
I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?
K4WYS


Hi Sonny

Would you consider using two lengths of 50 ohm coax, side by side?

Jerry

Sonny Hood wrote:

I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?
K4WYS

Sonny, the feedline cannot and does not have any influence on the
resonance of an antenna. Resonance is determined by the physical
dimensions of the antenna itself.

Tell us about the antenna. How did you determine a 100 ohm input impedance?

72 ohm twin lead is available at selected suppliers. But, I am not aware
of anyone making 100 ohm twin lead. that's why I asked about the 100 ohm
value.

Sonny Hood wrote:

I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?
K4WYS

Use side-by-side runs of 50 ohm coax to achieve a balanced Z0
of 100 ohms. Tie the braids together at both ends.
--
73, Cecil http://www.qsl.net/w5dxp

Dave wrote:
Sonny, the feedline cannot and does not have any influence on the
resonance of an antenna. Resonance is determined by the physical
dimensions of the antenna itself.

Feedline length has every influence on the resonance of
an antenna system if the SWR is not 1:1.

Why is a G5RV resonant on 3.7 MHz when a 102 foot dipole
is resonant on 4.6 MHz?

Truth is that the feedline can be used to resonate the
antenna system. I resonate my 130 ft. dipole on any HF
band by varying the length of the feedline. Check it out
at: http://www.qsl.net/w5dxp/notuner.htm
--
73, Cecil http://www.qsl.net/w5dxp

On Sun, 14 May 2006 16:34:44 -0400, Sonny Hood wrote:

I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?

To answer your specific question, ZIP cord is close to 100 ohms Zo.
However, it is relatively lossy (~3.5dB/100' at 10MHz).

K8ZOA measured ZIP cord characteristics and reported them here a year
of three back, Google for the info.

There were commercial low impedance twin lines for RF use, but they
are now obsolete (for good reason).

Owen
--

Cecil Moore wrote:
Sonny Hood wrote:

I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?
K4WYS

Use side-by-side runs of 50 ohm coax to achieve a balanced Z0
of 100 ohms. Tie the braids together at both ends.
--
73, Cecil http://www.qsl.net/w5dxp

Sounds like he may be trying to match a Quad or a Loop. If I am not
mistaken, the usual way to do this is with a 75 ohm Q section.
Side-by-side runs of 50 ohm coax with the braid tied together will
yield 25 ohms because they are in parallel. Not 100 ohms. Or do I
need to dive back into the antenna book?
Gary N4AST

better get out the snorkle... if you tie the braid and the center conductor
together you get a 25 ohm line, i use that all the time for my stack
matching boxes.

wrote in message
oups.com...
Cecil Moore wrote:
Sonny Hood wrote:

I have an antenna that needs 100 ohm twin lead to match the impedance
of the feed point. The 450 ohm lead has messed up the match and
screwed up the resonance, does anone know of such an animal?
K4WYS

Use side-by-side runs of 50 ohm coax to achieve a balanced Z0
of 100 ohms. Tie the braids together at both ends.
--
73, Cecil http://www.qsl.net/w5dxp

Sounds like he may be trying to match a Quad or a Loop. If I am not
mistaken, the usual way to do this is with a 75 ohm Q section.
Side-by-side runs of 50 ohm coax with the braid tied together will
yield 25 ohms because they are in parallel. Not 100 ohms. Or do I
need to dive back into the antenna book?
Gary N4AST

Cecil Moore wrote:

Dave wrote:

Sonny, the feedline cannot and does not have any influence on the
resonance of an antenna. Resonance is determined by the physical
dimensions of the antenna itself.


Feedline length has every influence on the resonance of
an antenna system if the SWR is not 1:1.


C'mon Cecil, you know better!

The antenna is resonant 100% by itself.

100 feet of wire is resonant within a few KHz of 4.68 MHz. Period.
120 feet of wire is resonant at ~ 3.9 MHz. Period.
65 feet of wire is resonant at ~ 7.2 MHz. Period.
33 feet of wire is resonant at ~ 14.2 MHz. Period.

You are tuning a non resonant antenna to resonance with your stubs.

You changed the scope of the discussion with the exact wording of your
response. You used "antenna system". I used "antenna".

Why do you persist in comparing alligators and kittens?

Dave wrote:
The antenna is resonant 100% by itself.

Most knowledgeable people know that the resonant frequency
of the antenna system can be changed by the length of the
transmission line series matching section. Why don't you
know that? Here is the SWR of my 130 foot dipole antenna
on 40m achieved by varying the length of the 450 ohm
transmission line.

http://www.qsl.net/w5dxp/swr13040.gif

Please look at that graph and then tell us that the feedline
cannot tune the antenna system to resonance.
--
73, Cecil http://www.qsl.net/w5dxp