A few years ago I put up a 230 foot long horizontal loop fed with 600
ohm ladder line. It was roughly in the shape of a quasi
trapezoid-rectangle and was ~ 25 feet up. I used it mostly on 80 and
40 meters. I figured it was just barely high enough to avoid ground
loss on 80 m. My noise level on that band was usually around S9 being
in town on a small lot.
A few weeks ago I took it down and put up a 130 foot long center fed
dipole at 45 to 50 feet fed the same way. This has been blowing away
the loop on 75 m. by 10 to 15 dB. The ground loss with the loop must
have been much greater than I expected it to be, the lesson there
being for me, that 25 feet is too low. A second comment is that the
noise level on the dipole is about 2 S units less and more important,
the RFI I used to get from local consumer appliances has vanished. My
guess is that the dipole is a bit more isolated from the small fields
these devices generate, by both being higher, and by not being near
the homes where these devices are located (the loop, being a loop was
near 3 homes). So, if you are in a city, consider that height may
get you some distance from consumer electronics noise.
Those of you concerned with common mode RF on coaxial feedlines but
desire the advantages of balanced feedlines should consider a balanced
link coupled tuner such as the Johnson Matchbox design since its
inductive coupling isolates the unbalanced low Z line to the shack
from common mode RF on the balanced feedline, without the use of any
choke balun.
73
Rob K5UJ
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