"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.

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.
--

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

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

"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.