Ralph Mowery wrote:
I have a 50 ohm swr meter (Heathkit, Drake W4 and Bird) and I am
using 70
ohm coax for a dipole antenna on 3.7 MHz.
If I trim the antenna for the lowest reflected power showing on the
meters,
will the antenna be cut to resonate (or near resonate) frequency or
is it
possiable the antenna will end up around 100 feet or 150 feet instead of
near a calculated frequency length of around 125 to 130 feet.

Guess the real question is can I use a 50 ohm meter with 70 ohm coax and
when the reflected power is the lowest, is the antenna system adjusted
correctly ?

I don't really worry about it, just stick up some wire and operate.
Adjust
things so the rig will see a low enough swr the internal tuner will take
care of it.


When your SWR meter reads 1:1, it means only that the impedance it sees
is 50 + j0 (50 ohms purely resistive). If you're using 70 ohm line, the
impedance at the antenna could be any of an infinite number of different
impedances, depending on the length of the coax. It might or might not
be resonant, but that won't make any difference to its performance. Your
transmitter will be happy with the load, so the antenna will get the
full rated output power less coax loss. It would be appropriate to call
that the "correct" adjustment of the antenna.

If the tuner has to adjust for some other load impedance (indicated by a
higher reading on the SWR meter), the tuner loss will be added. However,
it's likely to be negligible if the SWR meter is reading 2 or 3:1 or lower.

Roy Lewallen, W7EL