"Woody" wrote in news:hYdli.29709$BT3.8034@trnddc06:

Hi Owen. 5% was just a number picked out at random by me for
clarification of my question.
So you wouldn't want to share your 'sweet' findings, would you??
thanks!

W,

I have had a quick look for the spreadsheet and Perl scripts, but haven't
found them. I am sure I have them, but haven't filed them in an ordered
way apparently, I think that technically is lost... or galloping
senility.

The reason I didn't publish them as is at the time is is that they are an
incomplete picture.

Have a look at the article at
http://www.vk1od.net/InvertedL/InvertedL.htm which describes an InvertedL
at approximately one of those "sweet" lengths (~26m). In fact, the length
was juggled to avoid excessive feedpoint voltage on all bands.

Another of the "sweet" lengths is half that at 13m, and the voltage plot
is rougly scaled proportionately in frequency.

You will see from Fig 1 that the voltage peaks at higher frequency
parallel resonances are less an issue than the first and second
resonances (you can't see from the graphs, but ~10kV and 3kV
respectively).

Of course, none of this discussion addresses the pattern issues at the
higher frequencies.

As far as the earth system goes, it impacts efficiency of the system. It
is my view that the earth only needs to be good enough that its loss is
an acceptably low portion of the transmitter power. The shorter the
radiator in wavelengths, the lower its Rr and therefore the lower the
earth resistance for comparable efficiency. If you look at Fig 4 of the
article, you will see that Rr is 100 ohms or greater above 5MHz, so the
loss of an earth system resistance of say 30 ohms is near insignificant,
but at 80m where the length is relatively short, you need a better earth
for good efficiency.

Don't agonise over it too much, and treat the Rules of Thumb as ROT until
you understand the underlying assumptions and caveats.

Owen

W


"Owen Duffy" wrote in message
...




I have done just that, and searched for "sweet" wire lengths that
aren't within say 5% of band edge for all HF bands. It sounds like a
solution to the problem doesn't it. (5% implies that you have a
pretty determinate scenario, which is a big assumption. IIRC 10%+
will not give a practical result on the higher bands.)
Owen