Optimum length for ladder-fed dipole
 

I'm planning a dipole installation fed with ladder line and a
wide-range antenna tuner.

I'd like to be able to use it on 160 through 10. A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn' t do that?

Thanks...

Rick

Optimum length for ladder-fed dipole
 

Rick wrote:
A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn't do that?

The optimum length of feedline for feeding a 1/2WL dipole
on 160m is 1/2WL, i.e. about 233 feet. If you make the
dipole longer than 1/2WL, the optimum length of feedline
is less than 1/2WL which may be a benefit.
--
73, Cecil http://www.w5dxp.com

Optimum length for ladder-fed dipole
 

Rick wrote:
I'm planning a dipole installation fed with ladder line and a
wide-range antenna tuner.

I'd like to be able to use it on 160 through 10. A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn' t do that?

Thanks...

Rick

You might give some consideration to radiation patterns at the higher
frequencies where greater lengths will produce more pronounced lobes and
nulls and reduce broadside radiation. You might check cebik.com for
further information.

Chuck

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Optimum length for ladder-fed dipole
 

On Jan 28, 4:08 pm, chuck wrote:
Rick wrote:
I'm planning a dipole installation fed with ladder line and a
wide-range antenna tuner.

I'd like to be able to use it on 160 through 10. A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn' t do that?

Thanks...

RickYou might give some consideration to radiation patterns at the higher
frequencies where greater lengths will produce more pronounced lobes and
nulls and reduce broadside radiation. You might check cebik.com for
further information.

Chuck

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The couple of times I have tried a long antenna like this optimization
of the antenna was mostly finding a length the tuner was happy with on
all bands. IF you have a better tuner than my MFJ you may not have
this problem. Check Cecil's website, Hes the man when it comes to no
tuner antennas.

Optimum length for ladder-fed dipole
 

"Rick" wrote in message
...

I'm planning a dipole installation fed with ladder line and a
wide-range antenna tuner.

I'd like to be able to use it on 160 through 10. A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn' t do that?

Since you are using ladder line (assuming you use a suitable gauge for the
power transmitted), the dielectric and resistive losses losses are
insignificant even at relatively high SWR. I doubt it matters much whether
your feedline is 100 feet or 320 feet; most relected power will still get
transmitted out and not be absorbed as heat.

Optimum length for ladder-fed dipole
 

In message , Stefan Wolfe
writes

"Rick" wrote in message
.. .

I'm planning a dipole installation fed with ladder line and a
wide-range antenna tuner.

I'd like to be able to use it on 160 through 10. A half wave at 160
meters is a bit under 260 feet. Is there any particular reason I
should limit its length to 260 feet? I have enough room to make it
about 320 feet... any particular reason I shouldn' t do that?

Since you are using ladder line (assuming you use a suitable gauge for the
power transmitted), the dielectric and resistive losses losses are
insignificant even at relatively high SWR. I doubt it matters much whether
your feedline is 100 feet or 320 feet; most relected power will still get
transmitted out and not be absorbed as heat.



One answer as to what the optimum length of feeder should be is 'exactly
equal to the distance between the antenna feedpoint and the antenna
tuner'.

Being serious, be aware that one of Cecil's 'fortes' is the avoidance of
tuning unit losses by using a particular length of feeder, so that the
antenna plus feeder system naturally presents a good match for the
transmitter. On a given frequency, every length of antenna has an
optimum length of feeder, so you need to switch in the appropriate
length of feeder for each band. There is a lot of debate about how much
power you lose an antenna tuner. You may, or may not, want to consider
using this technique.

Your question was actually whether 320 feet would be better than 260
feet. When you go above a halfwave, the theoretical 'donut' polar
diagram starts to break up, but I doubt if you would see much difference
in the performance. Unless the antenna is pretty high above ground,
most of the radiation on 160m will be at a fairly high angle. A low
halfwave is fairly omnidirectional, regardless of the orientation of the
antenna.

Of course, on the higher frequency bands, the radiation will come
increasingly more off the ends of the antenna than broadside. On 10m,
it will probably be very directional, especially if the antenna runs in
a straight line.

Cheers,
Ian.
--

Optimum length for ladder-fed dipole
 

Stefan Wolfe wrote:
Since you are using ladder line (assuming you use a suitable gauge for the
power transmitted), the dielectric and resistive losses losses are
insignificant even at relatively high SWR. I doubt it matters much whether
your feedline is 100 feet or 320 feet; most relected power will still get
transmitted out and not be absorbed as heat.

And at some extreme impedances (accompanied by extreme
SWRs) losses mount in the tuner and balun if not in the
transmission line. I have a rule of thumb to keep the
ladder-line SWR below 25:1 which probably fits with
your "relatively high SWR" statement.
--
73, Cecil http://www.w5dxp.com

Optimum length for ladder-fed dipole
 

Ian Jackson wrote:
Being serious, be aware that one of Cecil's 'fortes' is the avoidance of
tuning unit losses by using a particular length of feeder, so that the
antenna plus feeder system naturally presents a good match for the
transmitter. On a given frequency, every length of antenna has an
optimum length of feeder, so you need to switch in the appropriate
length of feeder for each band. There is a lot of debate about how much
power you lose an antenna tuner. You may, or may not, want to consider
using this technique.

It's also not an either/or choice. Without a tuner, the
ladder-line length selector needs to be able to be
varied in one foot increments from zero to 31 feet.

Since I bought my IC-756PRO with its built-in auto-
tuner, I only switch between three lengths of transmission
line and allow the autotuner to do the rest. So now I
have a hybrid system, still not requiring a full-range
antenna tuner.

I've submitted a magazine article to "Worldradio" magazine
about a dipole that works very well on 75m, 40m, and 17m
without a tuner and without changing feedline lengths.
--
73, Cecil http://www.w5dxp.com

Optimum length for ladder-fed dipole
 

No reason to stick to a particular length of dipole... There is a
reason we use open wire instead of coax, and that is it works with any
length of antenna
some short length restrictions apply, bni, sar, ymmv, etc.
Put it up as long as you can, attach feedline, diddle tuner, and
go...
IF, and only if, you have problems tuning one band or another, then
shorten the dipole by 2% and try again...
Just do it... Don't think... And don't listen to me, what do I know!

denny / k8do

Optimum length for ladder-fed dipole
 

"Cecil Moore" wrote in message
.. .
Stefan Wolfe wrote:
Since you are using ladder line (assuming you use a suitable gauge for
the power transmitted), the dielectric and resistive losses losses are
insignificant even at relatively high SWR. I doubt it matters much
whether your feedline is 100 feet or 320 feet; most relected power will
still get transmitted out and not be absorbed as heat.

And at some extreme impedances (accompanied by extreme
SWRs) losses mount in the tuner and balun if not in the
transmission line. I have a rule of thumb to keep the
ladder-line SWR below 25:1 which probably fits with
your "relatively high SWR" statement.

Yes, I agree.