"Owen Duffy" wrote in message
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" wrote in news:6d1a078a-e5f4-
:
...
Though the traditional approach has been to use a 4:1 voltage balun at
the rig to feed these things, there is good argument to use a 1:1
Guanella balun (current balun), and it can be located outside the shack
and inboard shield effectively grounded to deal with common mode current.
You still need to minimise the length of coax operated at high VSWR, and
it would not be necessarily absurd to think about low loss coax.
Owen
Okay, then it might make sense to do this: Plan II
instead of using the balun is in the tuner, there is no reason
why I couldn't mount another 4:1 balun outdoors, and use a short run
of low loss coax back through the conduit into the operating room.
That would be about 15 feet of LMR-400 cable. I could go to 1/2 heliax
but would there be any benefit??
So, I would have balanced open-wire feedline from the dipole to
the 4:1 balun followed by a 1:1 common-mode RF choke with
the requiste RF ground for decoupling,
followed by the short run of low loss coax going back to a
unbalanced ant. port on the tuner. I'd still have coax in the mix,
but the 4:1 balun should hopefully tame the high impedance
excursions across the antenna operating range to
reduce the coax's losses at those points?
Otherwise it is going to be hard to get balanced line into the shack,
unless I pull it through the PVC conduit with the other coax cables.
Pete