It is my understanding that this Matchbox is a 9:1. The system gets good reviews on 80-10m. So if I am using this system, would I need to calibrate the NanoVNA using the coax, then get my measurements from the antenna or calibrate the NanoVNA as normal and get measurements from the entire system? I appreciate your detailed explanation.
Darrell
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On Aug 12, 2020, at 16:37, David Eckhardt <davearea51a@...> wrote:
?Not quite correct! Ladder line is a transmission line just like coaxial
line. However, they perform their function differently.
1) The center fed dipole is a balanced source/load - differential
source/load.
2) Ladder line is a balanced transmission line - differential
transmission line. It is the correct transmission line to connect directly
to a balanced/differential source/load (dipole). It does NOT participate
in radiation. As a transmission line, fields close onto themselves
(between the two parallel conductors) and do not open onto free space, so
no radiation occurs.
3) Coax is an unbalanced transmission line - common mode transmission
line. Fields are intended to close between the inner conductor and the
inside of the outer shield/braid. It is NOT the correct transmission line
to connect directly to a balanced/differential source/load (dipole).
4) If coaxial cable it is connected directly to a dipole, the outer
portion of the shield/braid WILL participate in radiation and gather noise
on receive that will couple into the antenna and receiver.
5) The correct manner in which to connect a coaxial transmission line
(unbalanced transmission line) to a dipole (balanced source/load) is
through a 1:1 current balun or common mode choke. This will prevent the
outer layer of the coaxial braid from participating in radiation and
coupling local noise into the antenna/receiver.
6) 4:1, 2:1, 9:1,.......are NOT appropriate for the purpose stated in
(5). These are TRANSFORMERS and NOT BALUNS.
7) If you MUST use a transformer for impedance transformation, follow it
with a 1:1 current balun or common mode choke.
Dave - W?LEV
On Wed, Aug 12, 2020 at 9:20 PM Darrell Carothers <rescuemedic1@...>
wrote:
I am slowly getting parts in to try my end fed long wire antenna. Correct
me if I am wrong. With a center fed dipole, the 300 or 450 ohm ladder line
feeding it is part of the antenna. I would think I would use my NanoVNA at
the end of the feed to check where it would be resonant and for SWR. If so,
would the coax feeding the end fed long wire antenna also be considered
part of the antenna and use the NanoVNA to measure accordingly? I am told
this doesn¡¯t need a counterpoise.
Am I correct or am I missing something?
Thanks
Darrell
N5FTW
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*Dave - W?LEV*
*Just Let Darwin Work*
Darrell Carothers