Wouldn't two 50 ohm cables in parallel result in 25 ohm impedance?
k4ia, Buck
K3# 101
Honor Roll 8B DXCC
EasyWayHamBooks.com
On 9/18/2017 10:06 PM, Wayne Burdick wrote:
On Sep 18, 2017, at 5:31 PM, Don Wilhelm <[email protected]> wrote:
Wayne,
Actually, parallel coax runs make a good choice for shielded parallel feedline. The paralleled
LMR-400 lines should produce a feedline characteristic impedance of 100 ohms. It is normal to
connect the shields together at both ends. At the antenna, the connected shields are left
floating, but at the rig end, are connected to chassis common (your BL2 ground lug) - perhaps
"floating" is what you meant by "unterminated". Are the shields connected at
the antenna end?
Yes.
As I recall, the matched impedance loss would be twice the loss of a single run
of the coax, but at reasonable distances and the low loss of LMR-400, it should
not be a problem at HF.
Agreed.
The advantages of using parallel coax for a balanced feedline is the same as
using coax over open-wire or ladderline. It can be run on or in the ground,
run next to or thorough conducting metallic surfaces, or coiled up with no ill
effects.
That’s what I was dealing with. The house was built in 1929, so in the crawl
space there’s legacy plumbing, knob-and-tube wiring, heating ducts, and spider
webs that at least look conductive.
Wayne
N6KR
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