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.

Optimum length for ladder-fed dipole
 

Rick wrote in
:


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

Rick,

It seems most people want to discuss optimum feedline length, though that
was not your question.

It turns out that it is quite challenging to obtain good efficiency from
a dipole less than about 35% of a wavelength long in the type of
configuration you propose. That sets a practical lower limit to the
length of the radiator.

On the other hand, the pattern changes with longer length. Probably the
most significant change occurs at greater than about 1.25 wl where the
pattern breaks up into additional lobes. Another respondent suggests such
pattern changes occur at greater than 0.5wl, but that is wrong. So, this
effect might set a practical upper limit if the pattern is an issue on
160m or a higher band if you intend multi-band operation.

So, if you made the dipole 320', it is 0.58wl on 160m, and 1.17wl on 80m.
The pattern will have two clear major lobes on both bands. You can't make
it short enough to avoid pattern break up on 40m without degrading
efficiency on 160m (though by only a small amount if you used 1.25wl on
40m).

As far as feedline loss, you know whether it is insignificant when you
have calculated the magnitude. Though others suggest that ladder line is
(always) insignificant, it is the loss in the ladder line that drives the
35% minimum practical length discussed above.

So, the choice depends, and probably mainly on whether you want to use it
also on 80m and 40m, and whether pattern is an issue.

Owen

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?

I used to have a "dipole" which was about 150 feet on one side and
closer to 200 feet on the other, fed with true ladder line (little
plastic insulators spaced every 6 inches, not the plastic-covered
stuff) up maybe 35 feet. Worked like gangbusters. Locals often
explained that I "got out" so well because my signal was halfway
there before it had to leave the wire. VSWR was often greater
than 10:1, but I didn't care.

--
--Myron A. Calhoun; 2001 Dunbar Road; Manhattan, KS 66502-3907
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member and Rifle, Pistol, & Home Firearm Safety Certified Instructor
Certified Instructor for the Kansas Concealed-Carry Handgun license