Posted by
Ron D'Eau Claire-2 on
Apr 21, 2005; 5:23am
URL: http://elecraft.85.s1.nabble.com/Using-XG1-to-measure-feedline-losses-tp377354p377361.html
Vic, KG4HTT wrote:
I tested the idea tonight, and got some surprising results. I attached the
XG1 to a 12 foot dipole, which I taped to the center of my 52 ft. loop (16 X
10 ft.) opposite the feedpoint... I cranked the RF on my K2 all the way up,
but left the audio at 9 o'clock to keep the signal from being too loud. I
measured 9 millivolts AC at the speaker output.
I then swapped out the 3/8 inch copper ladder line and attached 450 ohm
"window" ladder line...I was surprised to get a higher reading, 23
millivolts AC. That wasn't what I expected. I turned the XG1 down to the 1
microvolt setting and listened, and it was clearly louder and with a better
signal to noise ratio than what I heard with the fat ladder line. So I
swapped lines out again and tested the fat ladder line again. It was back
down to the 9 millivolt AC level again...
--------------------
You haven't described the tuner setup. You are absolutely right that you are
measuring the combined system losses, not just the feedline losses.
One BIG factor is whether you are using a balun in the system. I've yet to
find a balun that isn't unpredictable and frequently lossy when used in a
feedline with high reactance, that is any balanced feedline with an SWR much
above 1:1, no matter the type.
For just that reason I still use a link-coupled fully-balanced tuner when
feeding my doublet with open-wire line. It takes me 30 seconds to change
bands, but I've never seen any automatic system/balun combination that is
better and many that I've tried are much worse.
The losses in a balun all depend on just how high the SWR on the line is -
that is, how much reactance is present.
Thanks for sharing your results Vic!
Ron AC7AC
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