On Tue,8/2/2016 9:31 AM, Jim Thomson wrote:
N7WS was the first to publish on this, at least 20 years ago. I found it
in one of the ARRL Antenna Compendiums, which have a LOT of great stuff
in them. Wes set up carefully controlled experiments in which he wetted
ladder line and compared loss wet and dry. He showed that wet line was
lossier than coax.
Yes, it is low loss when suspended in free space in a vacuum. If it is
wet or dirty or in contact with most anything the loss goes WAY up.
## can u get the 300/450 ohm line..without the windows ??
Seems to me that 300 ohm TV type line back in the 60s /70s
had no windows, I remember it well. It was also available
in a windowed variety.
Ladder line can be built from wire and suitable spacers. There's a guy
who exhibits each year at Dayton who makes what look like nice spacers
for ladder line.
## along the same subject, back in the 70s, solid twinlead
was available in 75 ohm. Came in 2 x formats, small and large.
The large stuff would easily handle high power. Back then,
the kw rated 75 ohm twinlead was fed directly to the dipole,
then the other end had a PL-259 installed on it. Dunno if its
still available or not.
At least 25 years ago, I bought a "new old stock" 250 ft spool of Belden
"75 ohm kilowatt twin lead," not having a use for it at the time, but
figuring that someday I might. 10-15 years later, I used it to feed a
dipole in Chicago. I still have it. It's a pair of stranded copperweld,
#12 or #10 (I can look it up) completely encased in a heavy dielectric
and jacket. I also have an old Belden catalog that published loss data
for it. You can see it in a graph of loss data for various coaxes on
page 2 of k9yc.com/Coax-Stubs.pdf Note that nearly all of this is mfr's
published data, not measured.
About seven years ago, I helped N6RZ's widow dispose of his stuff. In
it, I found a few lengths of Amphenol's 75 ohm twin lead.
With no windows in the line, water wont collect.
Yes, but it could certainly collect on the jacket of that 75 ohm twinlead.
## On a similar note, a buddy used paralleled 50 ohm coax,
to make 100 ohm, shield, balanced line for his quad project.
Shield tied together at each end. 100 ohm Z between the
2 x center conductors. Made from 2 x 213-U taped together
every few inchs. Can also be done with 2 x RG11 to make
150 ohm, balanced, shielded line.
Yes, except that the runs you described have the lines
"series-connected" to yield twice the impedance. They could also be
parallel-connected to yield 25 ohms for two 50 ohm lines or 37.5 ohm for
two 75 ohm lines.
And as you probably know, the loss in dB in parallel runs of coax,
whether connected in series or parallel, is the same as in a single run
of the same coax.
73, Jim K9YC
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