Measure the SWR. Often the dipole impedance is closer to 50 than 75 Ohms,
and it is not worth doing anything about it, especially an inverted V.

If I remember correctly, an article on Inverted Vs a long time ago in _QST_
reported that an inverted V with its element at 45° from the horizontal (or
from the vertical!) had a 50-Ohm impedance, and a horizontal and vertical
radiation pattern kind of midway between a vertical and a dipole. I fed my
40m inverted V with 45° element angles with 50-Ohm coax. It had a
design-frequency SWR of ~1.1. SWR went up to ~1.5 at the CW high band edge.

NØKF


"Tarmo Tammaru" wrote in message
...
Tom,

There is a way of doing it, using two matching sections. It is described
in
either the ARRL Handbook, or Antenna Manual. It takes a length of 50 Ohm
coax (NOT 1/4 wave) + a length of 75 Ohm coax (NOT 1/4 wave) to match to
50
Ohms. If I run across it, I will post it.

Before you do all that, put up the antenna and feed it with 50 Ohm coax.
Measure the SWR. Often the dipole impedance is closer to 50 than 75 Ohms,
and it is not worth doing anything about it, especially an inverted V.
Certainly, don't do anything if your radio has a built in antenna tuner.

Tam/WB2TT
"Tom Sedlack" wrote in message
...
I asked this before and was told that for relatively short runs (under
50
ft), using 50 ohm coax to feed dipoles is fine.

I keep coming back to this in my head because I model a dipole and I get
a
VSWR of 1.5 using 50 ohm feed and I get 1:1 if I model with 75 ohm feed.

My plan for my little antenna farm is to have a run of 50 ohm coax to a
remote antenna switch. Create a few dipoles and feed them with 75 ohm
coax.
I saw an equation someplace that, I believe, gave the length of 75 ohm
feed
required to transform the impedance to 50 ohms at a given frequency. I
would
cut the cable to this length then connect to the 50 ohm antenna switch.

246 x Velocity Factor
L = -----------------------------
Freq


Does all this make sense? Am I going overboard (a curse of trying to be
a
perfectionist)? I don't want to use a tuner because; 1 - I don't own
one
and 2 - they waste power (I want to try QRPish operation).

Also, if the above is correct, would I still need to put a current choke
(coil of coax) or would the "fact" that the feed and dipole are matched,
there wouldn't be RF on the jacket?

My head is starting to hurt........


Tom