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.
--
73, Cecil http://www.qsl.net/w5dxp



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This means your shield has RF on it .
Also triming cable has nothing to do with SWR. Trimming the cable will
change the impedance the transmitter sees if the transmission line has
standing waves on it.


"Dr. Slick" wrote in message
om...
Hey,

I've been getting different readings on my power meter that
depend on the length of coax that i use to the meter (into a
Cantenna).

This is a push-pull VHF 300 watt transmitter with a coax stub
harmonic filter on the output. My digital Daiwa will read about 310
watts incident power using a 4 foot RG-8X jumper coax (from filter to
meter), and about 240 watts using a 12 foot section of RG-8X!!?? VSWR
stays the same at about 1.4:1 .

There is the old ham wife's tale that you can tune your
transmitter for a better match if you adjust the legnth of your coax
to the antenna. And from a theoretical point of view, it _should_ be
only a tale, because if your antenna is not a perfect 50 Ohms, the
length of the coax should still not matter, because the constant VSWR
circles around the center of the Smith Chart have just that, the same
SWR independant of the wavelengths away from the antenna (assuming 50
Ohm transmission lines are used).

OTOH, the actual series equivalent complex impedance will be
alternating from inductive to capacitive, every 1/2 wavelength.
So perhaps this will tune/detune the amplifier?

Any non-bullsh** advice/explainations appreciated.


Dr. Slick

"Jimmy" wrote in message . com...
This means your shield has RF on it .
Also triming cable has nothing to do with SWR.

In theory, yes. It would be on the constant VSWR circles, assuming
50 Ohm transmission line!

Trimming the cable WILL have something to do with the series
reactance that the PA will see, and may affect the impedance match.


Slick