DOUGLAS SNOWDEN, N4IJ, wrote:

I am planning on putting up a ground mounted vertical for
40 and 80 meters. Somewhere between 70-90 ft tall and
insulated from the ground. The antenna will be about
275 ft from the shack. My question: is it advisable to
feed a vertical with open wire feeder?

Consider using an UNBALANCED, open-wire line. It would consist
of three wires fairly close together with uniform spacing
between them. The center wire is "hot" and the outer two
are "ground". At the antenna, the two ground wires connect
to the ground radials and the center one connects to the
vertical radiator. At the shack end, your matchbox would
be configured to feed a "longwire" with the center wire
connecting to the "longwire" terminal and the two ground
wires connecting to the matchbox case (and shack ground).

No matching networks or baluns are needed at the antenna.
The line has a fairly high SWR on it, but also has low loss
and thus maintains efficiency. All matching is done in
the shack under your direct control.

The downside is that you would have to make the line yourself
out of ordinary house wire and plexiglass spacers and support
it off the ground on poles. If you used commercially available
ladder line, you would have to support it anyway, so that's
pretty much a wash.

I am thinking it would work ok either directly or through a balun
on one or each end of the feedline, but how does one keep the RF from the
radiator from unbalancing the line? Or would it just tend to hit both sides
of the line and not upset the balance?

The unbalancing issue goes away completely with this kind
of line. This scheme was widely used in broadcasting in
the 30's and 40's but fell out of favor because it required
a bit more maintenance than buried hardline.

Jim, K7JEB
Glendale, AZ