[Elecraft] Two Band Moxon/wire beam

[VR2BrettGraham]

W1CG replied:

<one big snip>

>>Presumably you know the dielectric constant of that insulation,
>>verified that the wire you have is in the same neighborhood &
>>done all your modelling based on that figure?
>
>I have previously assumed that any wire insulated or not, in space, has 
>the same velocity factor as bare wire.  Why wouldn't it?  I can see that a 
>twisted pair, or feed line would be affected by velocity factor.

Because, quite simply, it does.  You are not above the laws of
RF black magic - never were & never will be, full stop.

Shorten things by 2-3% - perhaps more - in your model & see
what happens.

That is what happens when you use insulated wire without
taking into consideration the effect of the insulation.

On 40m & somewhere around about a quarter-wave above
ground - without any consideration for the insulation - IMHO
nothing will be where you expect it to be.  It never is for me.

<snip again>

>Remind me what WA1X's approach is again.

Tune elements such that they are resonant reasonably close
to where they need to be - both driver & reflector.

In a nutshell, not really possible to make a Moxon without a
bit of tweaking.

Mine - made of wire that has very little dielectric in contact
with it (just the end insulators) - required quite a bit of trimming
before it showed reasonable match _and_ performance based
on pattern.  Remember, this was a 10m Moxon at a height of
wavelengths greater than yours above "ground".

Get higher up & things should change, but I really believe you
are taking a hit from these two very significant factors (with
ground _so_ close that it might be greater than the insulation).

Compare against another antenna & I suspect you will see - as
I did.

As for simultaneous operation, other than harmonics & spurs,
the other concern is phase noise & K2 is quite good in
that department.  Harmonics usually are more of a problem on
CW due to relationship of bands (less so in ITU R2, where
2 x 40m SSB band is mostly above 14.35 Mc).

But as this all has to do with evil competitive operation &
judging from lack of interest from the list, best to terminate
this discussion.

GL.

73, VR2BrettGraham