I have two stations, lets call them RIGHT and LEFT. With regard to my
loop antenna they are as follows. The antenna is apex UP and fed about
30' up from a bottom corner from the B tower. There is a 75 ohm
transformer and the RG213 remaining goes through a surge protector at
the base of the tower (POINT 1). The loop itself is tilted slightly
away from the base of the tower, probably about 20'. The antenna has
been up for a year now. Continuing, the coax goes 25' to a six position
dual feed coaxial switch (WX0B SixPak) (POINT 2) then another 180' with
buried hardline to the second tower. A two position coaxial switch
(ICE) (POINT 3) feeds the signal to the house (200' underground hard
line). The switch allows me to separate off the stations if one needs a
front tower antenna (A tower or a rear tower B). A second surge
protector at the house breaks the hardline from RG213 which continues to
the station which is located over the garage. The two stations are
about 25' away from each other. That is the only difference in the two
coax lengths. Both stations use the same equipment, a Yaesu XCVR for
the low bands, a 781 for the high bands and an Alpha87 amp.
I was going to operate the ARRL 160m from the LEFT station, but I
noticed the VSWR on the loop was quite high. It was at least 3:1 and
the amp kept tripping out. The RIGHT station had its normal VSWR which
is quite low. I abandoned the test and decided to trouble shoot.
Since my Autek device never measured 160m antennas well, I took a 751A
transceiver to POINT 1 and POINT 2 and found the VSWR to be quite like
the LEFT station. As a matter of fact, there was a small dip going to
the bottom of the band, so I shortened the bottom corners by 6' per side
and the antenna looked quite good with a 1.2"1 at 1815 or so. I
measured the VSWR at POINT 2 and it was also good. I went to the
station and found the RIGHT station VSWR now had INCREASED at the amp to
about 100w reflected from about 20 before I started. I wish I could say
that the LEFT station was great now, but a relay problem with the SixPak
prevented the station from transmitting and I will just need to repair
the unit.
So you probably want to know why the RIGHT and LEFT setup? The LEFT is
for contesting and the RIGHT shares three transceivers (also an Orion)
which is my internet remote control station rig. So, I rarely use the
LEFT station. My questions are why could a VSWR that was seemingly so
bad look terrific at one station and so bad at the other with the only
difference being an extra 25' of coaxial cable and different equipment?
I am presuming the CORRECT VSWR is the reading of the radio at the base
of the tower and each point down the line. I never adjusted the antenna
for VSWR last year as I presumed the number I was seeing was identical
on the LEFT station, mistake. Should I now see some better performance
from the loop as the VSWR is less? Why would an extra 25' of coax
matter the station POINT 3 and not POINT 1 vs POINT 2?
Thanks for the help and I appreciate any insight from my learned colleagues!
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