On 8 Dec 2006 05:05:33 -0800, "4nec2" wrote:

....
Below the Nec-file with Tr-Line lengths as calculated above and a third
50 ohm line from
stub junction to the house.

Delivering a Z-in of 0.93 + j 24.2 ohms ?, If you ask me this should
have been around 50 ohms.

CM Short Inverted V for 80 Mtr.
CE
GW 1 25 -9.829825 0 14.117083 -0.3 0 21 5e-4
GW 2 3 -0.3 0 21 0.3 0 21 5e-4
GW 3 25 0.3 0 21 9.8298245 0 14.117083 5e-4
GW 989 1 -0.1 0 0.5 0.1 0 0.5 5.e-4
GW 998 1 -0.1 16.72 8.09 0.1 16.72 8.09 5.e-4
GW 999 1 -0.1 0 8.09 0.1 0 8.09 5.e-4
GE
LD 5 0 0 0 58000000
GN 2 0 0 0 14 .006
EX 0 989 1 0 1 0
FR 0 1 0 0 3.6
TL 2 2 999 1 50 19.5606
TL 999 1 998 1 300 20.9
TL 999 1 989 1 50 7.59
XQ


Arie,

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

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

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.

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.

Owen
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