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

Sounds like too much work! The loss of 50 Ohm feedline at 80 and 40 meters
isn't worth worrying about.


"K7JEB" wrote in message
news:udpSb.13355$tP1.11645@fed1read07...
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

Dr. Daffodil Swain wrote:
Sounds like too much work! The loss of 50 Ohm feedline at 80 and 40 meters
isn't worth worrying about.

For 275 ft. of RG-58 with an SWR of 1:1 on 40m, one would lose
~half of one's power in the feedline. With an SWR of 10:1, one
would lose ~75% of one's power in the feedline.
--
73, Cecil http://www.qsl.net/w5dxp



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I made the mistake of assuming one would not be stupid enough to run 275
feet of RG58.

"Cecil Moore" wrote in message
...
Dr. Daffodil Swain wrote:
Sounds like too much work! The loss of 50 Ohm feedline at 80 and 40
meters
isn't worth worrying about.

For 275 ft. of RG-58 with an SWR of 1:1 on 40m, one would lose
~half of one's power in the feedline. With an SWR of 10:1, one
would lose ~75% of one's power in the feedline.
--
73, Cecil http://www.qsl.net/w5dxp



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Dr. Daffodil Swain wrote:
I made the mistake of assuming one would not be stupid enough to run 275
feet of RG58.

You said:

The loss of 50 Ohm feedline at 80 and 40 meters isn't worth worrying about.

RG-58 *is* 50 ohm feedline. Aren't you glad I didn't choose RG-174? :-)
--
73, Cecil http://www.qsl.net/w5dxp



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"Cecil Moore" wrote in message
...
Dr. Daffodil Swain wrote:
Sounds like too much work! The loss of 50 Ohm feedline at 80 and 40
meters
isn't worth worrying about.

For 275 ft. of RG-58 with an SWR of 1:1 on 40m, one would lose
~half of one's power in the feedline. With an SWR of 10:1, one
would lose ~75% of one's power in the feedline.
--
73, Cecil http://www.qsl.net/w5dxp

275 feet of garden variety RG8Foam would have a loss of about 1.5 db at 10
MHz. LMR400 about 1db. Do NOT use RG213.

Tam/WB2TT

"Tarmo Tammaru" wrote in message
...

....

275 feet of garden variety RG8Foam would have a loss of about 1.5 db at 10
MHz. LMR400 about 1db. Do NOT use RG213.

What's wrong with RG213?
__
Steve
KI5YG
..

K7JEB wrote:
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".

Hi Jim, what would be the range of Z0's possible with this configuration?
--
TNX & 73, Cecil http://www.qsl.net/w5dxp



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I originally wrote:
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".

Cecil, W5DXP asks:
Hi Jim, what would be the range of Z0's possible with this
configuration?

Jasik has a formula for this type of line:

Zo = (207/sqrt(epsilon))*(log(1.59*(Dist/dia)))

where Zo is in ohms, epsilon is relative dielectric constant
of surroundings (=1.0 in this case), sqrt is the square root
function, log is the base-10 logarithm function, Dist is the
distance between the center wire and one of the outside wires
and dia is the diameter of the wires used, Dist and dia being
in the same units.

Setting dia=0.116 inches (#10 AWG stranded wire) and varying
Dist gives:

Dist = 1.0 inch ............ Zo = 235 ohms
Dist = 2.0 inches .......... Zo = 297 ohms
Dist = 4 inches .......... Zo = 360 ohms
Dist = 10 inches .......... Zo = 442 ohms

The trade-off would be between the desireable high impedance
from wide spacing and leakage suppression from close spacing.
Dist=4 inches looks about right.

Although I haven't tried it, my guess is that common electric-
fence hardware would be adequate for supports and insulation,
but the conductors should be copper (and #10 gauge). Stacking
the conductors vertically should simplify the mechanical aspects
and possibly partially suppress sky-wave leakage from the line.

Jim, K7JEB
Glendale, AZ