Almost correct.

The transmitter output impedance has no effect whatsoever on the line's SWR.

Roy Lewallen, W7EL

Dr. Slick wrote:
W5DXP wrote in message ...

Jimmy wrote:

I hope this is a wifes tale that has long been discredited. Trimming cable
changes the impedance seen by the transmitter with no change to SWR.

However, a 50 ohm SWR meter reading will change as one changes the
length of the ladder-line. When the 50 ohm SWR meter reads 1:1,
the transmitter is seeing 50 ohms. That's how I tune my dipole.



This is very interesting, as it may indicate that the "wife's
tale" may have some validity in _some_ cases.

For example, if your antenna happens to have an impedance of say,
60 Ohms, and your transmission line happens to NOT be a perfect 50
Ohms (usually the case), and happens to be around 54.8 Ohms or so...
then at odd integer multiples of 1/4 wavelength (velocity factor
included, of course), you will be right on 50 Ohms.

Additionally, as we have mentioned before, PAs rarely have 50 Ohm
output impedances anyways (who actually measures this??). So an
impedance transform via perfect 50 ohm coax length may indeed get you
closer to a conjugate match and higher incident power, which may
improve your VSWR (which is based upon the incident and reflected, of
course).


Slick