Hi Guys,
I put up Bobtail Curtain antenna for 20 meters for the CQ DX contest
this afternoon. It is fed at the center vertical element. Here is the
problem. It requires a matching network (tank circuit) at the feed
point. So I took my MFJ-269 antenna analyzer out to the feedpoint and
tuned the antenna. I got it to 1.1 to 1. I then went inside and found
that I have a 3.9 to 1 swr measured both with the analyzer and the
internal wattmeter on my K2. I have never measured feed point impedance
before I always just tuned antennas by measuring SWR at the transmitter.
Now, I feel like the guy in the old Chinese proverb with two
wristwatches and never knowing what time it is!
I added some ferrite beads at the feedpoint to ensure that it isn't
common mode currents on the outside of the coax sheild causing this. I
always thought that SWR doesn't change along a transmission line. What
is causing this I wonder, and should I just tune the antenna for lowest
SWR at the transmitter regard less of feedpoint SWR?
Thanks in advance,
Bob K6GGO
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