"Dr. Slick" wrote in message
om...
W5DXP wrote in message
...

Remember the maximum power transfer theorem? The transmitter probably
works
better into some impedances than into others. With an SWR of 1.4:1, the
transmitter will see a resistance between 35.7 ohms and 70 ohms with a
reactance
between zero and about plus or minus j15. Knowing the frequency and VF
of the
RG-8X, you should be able to estimate the two impedances seen by the
transmitter.


Actually, i read off of my Smith Chart about +/- j20, but you are
close.

Anyhow, my point is that the ham "wife's tale" of adjusting the
coax length for lowest SWR may be truly just a tale.

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. It is
true that there are a lot of people who dont understand the difference.

However, in my case, the SWR doesn't change much, while the
INCIDENT power does!!! To me, this may be due to the fact that the PA
isn't 50 Ohms at the output (I'll bet not many really are), and so a
swing of +/- j20 may improve or degrade how close you are to a
conjugate match.

What do you dudes think?


Dr. Slick

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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