On Apr 5, 12:13*am, Tom Horne wrote:
K7ITM wrote:
On Apr 3, 9:38 pm, Tom Horne wrote:
I realize this may be a terribly basic question but at any given
transmitter power will the highest current measured in the antenna feed
line occur at the lowest SWR or not.
--
Tom Horne

"This alternating current stuff is just a fad. *It is much too dangerous
for general use." *Thomas Alva Edison

At the lowest SWR, 1:1, the steady-state RMS current along a lossless
transmission line is everywhere the same. *At high SWR, the steady-
state RMS current along a lossless line varies between some high value
and some low value; the SWR is the ratio of the high value over the
low value, assuming the line is long enough that you won't find higher
or lower by extending the length of the line.

If the antenna feedpoint impedance is, say, 10 ohms and you feed it
100 watts, you should measure sqrt(10) amps at the feedpoint. *You'd
have a 5:1 SWR on a 50 ohm line with that load. *With a 250 ohm load,
you'd also have a 5:1 SWR on the same line, but the current at the
antenna end for 100 watts delivered to the antenna would be sqrt(0.4)
amps, or 1/5 as much current. *If the antenna represents a 50 ohm load
on the same 50 ohm line (swr = 1:1), the current is sqrt(2) amps for
100 watts, an intermediate value.

Hope that helps (and that I haven't screwed up my mental arithmetic).

Cheers,
Tom

Tom

If you have the patience please bare with me as I'm hoping to learn
something here. *I was trying to figure out what use if any could be
made of a current measuring device located at the antenna feed point.
What relationship would there be between maximum current at the feed
point and affective radiated power. *I've been told in both my license
preparation classes that making sure that the transmitter sees a low SWR
does not insure a good signal out of the antenna. *I'm looking for some
way to actually measure the amount of energy that is getting to the
antenna since it seams impractical to measure the signal strength in the
near or far fields during operation of the transmitter.

--
Tom Horne

"This alternating current stuff is just a fad. *It is much too dangerous
for general use." *Thomas Alva Edison- Hide quoted text -

- Show quoted text -

Monitoring the current would be of about as much use as monitoring any
other single parameter lets say VSWR. Once optimal values are
established it would provide a useful reference to monitor the
condition or changes in your system. Should a significant change occur
it is important to find the correct cause of the change. In the case
of current or VSWr one could make adjustments to make either read the
nominal value but this may not correct the actual problem.

Jimmie