"Jerry" wrote
would you advise using a (4 to 1) balun with the open wire on one
side, and a short run of coax, say 20 feet or so on the other to the
antenna
tuner? Would this work well? Does one need to 'make' the open wire
feeder,
or is the commercial stuff you buy ala ham coax suppliers good enough?

=================================

To add a length of coax, balun or not, to the end of a long, beautiful,
exceedingly low-loss, open-wire transmission line should be regarded as a
criminal act worse than horse-stealing and be made a hanging matter.

The correct, most efficient arrangement is to connect the line direct to the
tuner via a 1-to-1 current (choke) balun. The length of coax between tuner
and transmitter can then be as long as is necessary to reach.

A great length of coax, a horrid lump of capacitance, on the antenna side of
the tuner will also restrict its impedance matching range and possibly
increase tuner losses.

A 1-to-1 choke balun is just a few (8 or 10) turns of twin speaker cable (18
or 20 gauge) wound on a ferrite ring, or more turns on a ferrite rod with a
length of the same order as the ring's diameter.

The actual impedance of an open-wire line is of no consequence. It so
happens when the wires are spaced apart 100 times wire diameter Zo is about
600 ohms. 18-gauge wires spaced 4 inches = 600 ohms.

14-gauge wire spaced 2 inches makes a nice line. At 30 MHz, loss = 0.15 dB
per 100 feet. With SWR = 6, loss = 0.48 dB. When used as a 1/4-wave matching
transformer, Q = 550.

The problem is flexing in the wind and metal fatigue. But amateurs don't
need a feedline to last a lifetime - projects don't last that long. Very
tedious to homebrew so most people seem to settle for 450-ohm ladder-line.
Choose the heavier wire gauges. Don't bother with flimsy 300-ohm ribbon
stuff.

Problems involved with extending lines into the shack, like Mark Twain's
death, are much exaggerated. Insulate the wires and bring them close
together through a single hole in a window frame or even a wall. A little
extra capacitance due to close spacing over a length of a few inches is
electrically entirely un-noticeable. You've only to look at it to realise
that. Ignore gobble-de-gook about impedance bumps on lines intended to
operate with high efficiency at high SWR.

If you like amusing yourself with numbers, to analyse performance of any HF
dipole with any arrangement of twin-line + coax line + balun + tuner,
download program DIPOLE3 from website below.
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Regards from Reg, G4FGQ
For Free Radio Design Software
go to http://www.g4fgq.com
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