On Jun 20, 8:04*am, "Pete Bertini" wrote:
Just curious if this has ever been done? *I'm thinking about
putting up a 90 foot dipole feed with homemade open wire
line. *I'd like to bring it into the shack using paralled runs
of LMR-400 cable, since the final 25 feet is via 3" electrical
conduit that also has rotor and other cables.

I believe the parallel cables with give me a 100 ohm impedance.
The open wire will be using #10 with homemade spreaders,
I'm going to try for 600 ohms at the feedpoint. I was wondering
if tapering the spacing on the feedline would give me a smoother
impedance where the open wire, arrestor, and twin coax arrange-
meet?

Pete k1zjh

Based on my personal experience trying to replace the inside shack
portion of 600 ohm open feed line with two parallel pieces of RG-213
about 8 ft. long. The coax sections will effectively kill the use of
your dipole on any of the higher frequencies. As I remember, the
antenna was usable up through 10 meters , but after putting in the
coax, I couldn't tune the system above 20 meters.

My antenna is a full sized 160 meter horizontal loop in the form of a
trapazoid, almost a square, up at 35 ft. Fed in one corner with 600
ohm open wire,125 ft. long. The feedline comes into the house (mfg
home with aluminum siding) using two Birnbach feed through insulators.
Then to a DPDT antenna switch to ground the system during thunder
storms, and finally about 6 ft of 600 ohm feed line to the balun in
the Dentron MT-3000 tuner.

I think the problem with using the double coax is the very large
capacitance it adds to the feed line, effectively becoming a low pass
filter. Could be mistaken about the cause, but not the symptoms. I
have actually used the system to make some local 6 meter contacts.

Try it anyway, but be prepared to go all the way to the shack with
your 600 ohm feed line.

Paul, KD7HB