I used to use tuners.? No more.? I cut my antennas so that they are in resonance or close.? If I want to operate too far from that frequency I might use a tuner for just that although the efficiency sucks.? And of course the pi network in my amplifier does the job of a tuner.? If the mismatch is more than about 2:1 I balk even with a tuner.
So my old MFJ 986 sits in the closet.? Maybe good swap material.
Incidentally I have discovered that if you only trim one end of a dipole, the resonant frequency changes but the match at resonance deteriorates.? The upside is that the curve is a bit flatter so it covers a wider band.? This has been carried to extremes by the OCF dipoles that aren't very good antennas at any frequency, in my opinion
Bob
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On Wednesday, August 12, 2020, 03:30:41 PM PDT, Dave <dave@...> wrote:
Darrell:
? I initially make a wire antenna a little longer than the formula
calls for(it's easier to cut than to add wire).? Put up without the
autotuner.? Check with the nanovna or an SWR meter(the vna gives more
info).? Then trim so the lowest SWR is where you will be operating.? If
the lowest SWR is at a freq below where you want, cut a little wire off
each end.? If the SWR is above the freq you want to operate at, you
will? need to add wire.? Once the trimming is done, then you can add the
auto tuner if needed.
Dave - WB6DHW
On 8/12/2020 3:07 PM, Darrell Carothers wrote:
Thank you. Excuse my beginner questions but it seems I have a lot to learn. I will be using a auto tuner. I was just trying to find out what my SWR would be on the different bands and where it would be resonant on each band so I could attempt to find out if I need to trim it to tune it a bit. I guess I need to do more research before I attempt to put it in service.
Darrell
Sent from my over-rated IPhone 7 Plus.? Any Mis-spellings or grammar errors are due to my IPhone auto correct feature.
On Aug 12, 2020, at 16:59, David Eckhardt <davearea51a@...> wrote:
?As far as a counterpoise goes:? As a single-ended, common mode source/load,
the fields must go somewhere.? They don't just abruptly stop at the feed of
the EFHW (end fed half wave).? Yes, the coaxial feed WILL participate in
radiation as it forms the counterpoise to the EFHW.? Some form of
decoupling must be supplied before it connects to the radio or matching
network (a.k.a., 'antenna "tuner"') or there will be "RF In the Shack".? A
current choke or common mode choke installed before the coax connects to
the radio or matching network would be appropriate.? Then you can connect
the VNA to that point AFTER the current balun or common mode choke.
Without that, the VNA and anything holding onto the VNA or capacitively
coupled to the VNA will become part of what you measure and part of the
antenna.
Dave - W?LEV
On Wed, Aug 12, 2020 at 9:37 PM David Eckhardt via groups.io <davearea51a=
[email protected]> 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
Sent from my over-rated IPhone 7 Plus.? Any Mis-spellings or grammar
errors are due to my IPhone auto correct feature.
--
*Dave - W?LEV*
*Just Let Darwin Work*
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*Dave - W?LEV*
*Just Let Darwin Work*
