On 10/11/2011 5:59 PM, Owen Duffy wrote:

You gave lots of info on the system, well done, but ommitted the preferred
feed line length.

It may well be that your preferred feedline length should dictate the
dipole length.

Lessee, I have standoffs holding the present window line, and can back
of the envelope this. five feet to the roofline, then 25 feet to
transition to where it heads verticaly. Then allowing for some droop,
I'd say another 40 feet given the 20 foot roof height.

So we're looking at around 90 feet total, not counting the foot or so in
the house.

- 73 de Mike N3LI -

Michael Coslo wrote in
:

So we're looking at around 90 feet total, not counting the foot or so
in the house.

One of the risks of using a centre fed dipole with arbitrary open wire
feed is that you may find the impedance at the tx end of the line to be
extreme on some bands, driving problems with volage baluns, and ATUs.

In the case of a 80m half wave, feedline lengths near 60' and 180' are
likely to be troublesome. Same dipole on 40m and feedline lengths near
60' and 120' are likely to be troublesome.

Some folk would advise feeding at a current maximum, but of course, for
this dipole, a current maximum for 80m at the tx end of the feedline is
a voltage maximum for 40m.

Your 90' option might well be effective in avoiding some of the
impedance extremes on the lower bands that damage componets, cause
excessive loss, or are just difficult to match.

Owen