On Fri, 08 Dec 2006 20:36:22 GMT, Owen Duffy wrote:

Richard, at 5am I was just being lazy with quick cut and pastes. Its
all right for you, you have had breakfast and are all fired up!

Hi Owen,

Actually, here I'm entering the afternoon, post-carbohydrate slump.

73's
Richard Clark, KB7QHC

On Fri, 08 Dec 2006 12:10:36 -0800, Richard Clark
wrote:

On Fri, 08 Dec 2006 19:27:30 GMT, Owen Duffy wrote:

Z of 2.11171146485231-j6.26228362468365 or VSWR of 22:1.

What went wrong?

14 Place resolution in a field that struggles to be 20% accurate?

C'mon, Owen, saying 2 - j6 Ohms would be more readable and hardly
invalidate any premise being offered.

Richard, at 5am I was just being lazy with quick cut and pastes. Its
all right for you, you have had breakfast and are all fired up!

The important thing is that if you plug the numbers from Cebik's
spreadsheet into NEC (properly terminating the o/c stub), they should
be very close to a perfect match... but even a theoretical model
considering line loss will produce a very different answer. Even more
prospect of departure when practical tolerances are considered as you
note.

Owen
--

Owen Duffy wrote:
Even more prospect of departure when practical
tolerances are considered as you note.

I've always thought if the simulations can get me within
20%, I can do the rest by cut and trying.
--
73, Cecil http://www.w5dxp.com

Hello Owen, excuses for the delay, because I was caught by a very bad
cold...

Your design is for an o/c stub. Haven't you modelled a s/c stub by
connecting the transmission line to W998?

No, at least it was not meant to be. When TL cards are specfivied
without
additional real- and imaginary shunt admittance values they are to be
considered as an open end, although a dummy wire/segment is need
for connecting the TL end.

I have checked your proposed design on Winsmith, and it gives a 50
ohms input impedance.

Aha, nice to know. It seems the Cebik program is not in error.

Nevertheless, it is hypothetical as it is not
practical to connect a 300 ohm stub to 50 ohm line, 50 ohm line will
be coax (in practical cases) and it is not practical to make a 300 ohm
coax. If you were to mix coax and open wire line, you have a serious
balance issue that you have not dealt with in your model.

Yes, I know.

Who told you that the 50 ohm line was not symmetrical... (hi, hi, joke)

The other thing about the design is that two of the transmission line
elements are very close to 90 deg in length, which means that
operation is very sensitive to frequency change.

That's an interesting aspect of the situation.

If you really want to make a 40m inverted v work well on 80m, you
might have to match at the feedpoint. It is hard to get an unloaded
dipole of length 25%wl to work well without matching at the feedpoint.

The specified problem was only hypotetical, and does not exist in real
life (at least overhere).

Thank you, and the other posters, for the feedback,
Arie.