The only thing left that I'm not sure about is the true length of the
element for 17m. I have read that the length on page 4 of Cobwebb revealed
for this band is wrong.

It says the Tapping point 2300 and the length 4400.

Is the Tapping point correct and the length wrong or are they both wrong?

What should they both be?

Many thanks


"Dave Platt" wrote in message
...
In article ,
Barrett wrote:

Ok Dave, I will see what I have in the shed.
Trouble I have is that I only have a SWR meter to do the tuning and I
have heard the thickness of the wire can change the length of wire used
by
quit a lot. So I really needed to get it very close for the tuning as I
don't have an analyzer to use.

At these frequencies, the diameter of the wire is such a small
fraction of the antenna's length that small changes in the diameter
aren't going to matter very much.

As far as tuning and reproducibility goes, there's going to be a
bigger issue with this sort of antenna design (or any made from this
type of wire) - stretching of the wire under tension. This sort of
stranded, soft-drawn copper wire is prone to stretch quite a bit under
tension, both immediately and over time. You're likely to find the
antenna's tuning changing a bit, at least, over the course of its
lifetime, as the wires sag and stretch under their own weight.

Wire antennas are often made of "hard-drawn" copper wire, or of
soft-drawn wire which is pre-stretched to avoid such sagging and
de-tuning. I'm not sure whether zipcord-type appliance or speaker
wire could/should be pre-stretched in this way - I suspect that the
PVC insulation might be weakened by doing so and that the wire might
snap.

Question about the elements.

Does the speaker wire need to be kept very straight (no twisting) or
doesn't
it matter if there twisted?

I wouldn't twist it tightly - this _might_ add enough inductance to
alter the tuning by a detectable amount. A bit of loose twisting
ought not to matter. I don't think you have to be pedantic about
keeping it absolutely un-twisted.

As to tuning and SWR - as long as your rig has some sort of basic
autotuner that can handle a moderate SWR (say, 3:1 or better), and as
long as you get the antenna's tuning reasonably close (SWR minimum
somewhere inside each band you're going to be using), and as long as
you use a not-too-terribly-long run of good coax (RG-8 thickness
preferred), I really don't think you have to worry about trying to get
the lowest-possible SWR for the antenna itself. At HF, the amount of
"excess loss" in the cable, and in the ATU due to a moderate SWR is
not large, and probably will not make an appreciable difference in
your ability to either hear or be heard.



--
Dave Platt AE6EO
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