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

Dave wrote:
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.

Nobody said anything about tying the braid and center conductor
together. If the side by side run of 50 ohm coax is used as a
parallel feedline, the braids are tied together and the Z0
is 100 ohms when the center conductors are connected across
the load.
--
73, Cecil http://www.qsl.net/w5dxp

you are great cecil, you cut out the original post to make it look like i
had nothing to do with the original statement... if you will remember he was
asking if he would get 25 ohms if he connected the braids together without
the center conductors... i simply say that if you connect both the braid and
center conductors you get a 25 ohm line... the implication being that if you
don't connect the center conductors you don't get a 25 ohm line.

thanks for keeping the fight thread going so well, now that you are riled up
i guess you can branch out into some other threads and bog them down for the
rest of the week.

"Cecil Moore" wrote in message
. com...
Dave wrote:
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.

Nobody said anything about tying the braid and center conductor
together. If the side by side run of 50 ohm coax is used as a
parallel feedline, the braids are tied together and the Z0
is 100 ohms when the center conductors are connected across
the load.
--
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
--

"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

As I remember, common lamp "zip" cord (AWG 18 or 16) functions at about that
Z (I'll have to check)

gb

"g. beat " @spam protected wrote in message
...
"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

As I remember, common lamp "zip" cord (AWG 18 or 16) functions at about
that Z (I'll have to check)

gb
I once measured some cheap zip cord at 7 MHz. got something like 85 Ohms.

Tam/WB2TT

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?
K4WYS


Is this a single band or multiband antenna? If I recall correctly,
you can use a different impedance feedline if it is a multiple of a
half wave. At the half wave points, the impedance is the same as the
beginning of the feed.

Cecil or others here will correct the length error if I am incorrect.
But I learned about a year ago that the impedance can be corrected by
the multi-fraction length feedline of a different impedance.

Maybe this is the principal of Cecil's feedline matching system.

73 for now


--
73 for now
Buck
N4PGW

Buck wrote:
Is this a single band or multiband antenna? If I recall correctly,
you can use a different impedance feedline if it is a multiple of a
half wave. At the half wave points, the impedance is the same as the
beginning of the feed.

i.e. at the antenna. You're right, neglecting losses, the antenna
impedance is repeated every half wavelength. Neglecting losses,
that 100 ohm antenna feedpoint impedance will be repeated at half-
wavelength intervals for *any* feedline Z0, including 50 ohm coax.

Cecil or others here will correct the length error if I am incorrect.
But I learned about a year ago that the impedance can be corrected by
the multi-fraction length feedline of a different impedance.

Maybe this is the principal of Cecil's feedline matching system.

The principal of the feedline matching system that I use is that
every SWR circle crosses the purely low resistive point at a
current maximum point. For dipoles that are 1/2WL on the lowest
frequency of operation, the current maximum point is the ideal
point at which to feed the antenna system. Adjust the length of
the feedline until the current maximum point is at the transmitter
and you will usually not need a tuner at all.
--
73, Cecil http://www.qsl.net/w5dxp

On Mon, 15 May 2006 14:26:11 GMT, Cecil Moore
wrote:

Buck wrote:
Is this a single band or multiband antenna? If I recall correctly,
you can use a different impedance feedline if it is a multiple of a
half wave. At the half wave points, the impedance is the same as the
beginning of the feed.

i.e. at the antenna. You're right, neglecting losses, the antenna
impedance is repeated every half wavelength. Neglecting losses,
that 100 ohm antenna feedpoint impedance will be repeated at half-
wavelength intervals for *any* feedline Z0, including 50 ohm coax.

So far, so good. If the antenna is fed with 50 ohm coax, there will
be great losses, however, if I am correct, there will be negligible
losses with 450, or even less with 600 ohm twin-lead. A 2:1 balun at
the end of this 600 ohm wire should net a low-loss, but good match for
his antenna?


Cecil or others here will correct the length error if I am incorrect.
But I learned about a year ago that the impedance can be corrected by
the multi-fraction length feedline of a different impedance.

Maybe this is the principal of Cecil's feedline matching system.

The principal of the feedline matching system that I use is that
every SWR circle crosses the purely low resistive point at a
current maximum point. For dipoles that are 1/2WL on the lowest
frequency of operation, the current maximum point is the ideal
point at which to feed the antenna system. Adjust the length of
the feedline until the current maximum point is at the transmitter
and you will usually not need a tuner at all.

OK, I think that is a more technical explanations of what I said, so
we are in agreement. But for the sake of clarification, let me ask
this...

I have a yagi with about 25 ohms at the antenna. I connect 600 ohm
twin-lead and run it 1 1/2 wave lengths to my radio. This, I assume,
gives me the highest current at the end of the twin-lead. So I
connect it directly to the radio with a PL-259 and get an acceptable
load for the transmitter with low-loss in the feedline?


--
73 for now
Buck
N4PGW