Balanced feedline for vertical antenna?
 

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? 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?

Doug, N4IJ

DOUGLAS SNOWDEN 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? 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?

I would make the last 50 ft of transmission line to the vertical be coax and
install a good balun/matching network between the open-wire and coax.
--
73, Cecil http://www.qsl.net/w5dxp



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Doug,
I would think it would just depends on if you plan on
using some kind of matching/tuning system at the base of
the tower. If you do, then I'd use coax to the tower.
But you can do the same thing with ladder line, I'd just
find it easier to 'string' (actually, bury) the coax.
As for the RF 'messing' with the ladder line, it probably
won't make a lot of difference.
'Doc

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

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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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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Balance woun't be the problem, Doug. The problem is that over that long a
run, the feedline will radiate, and become a major part of the antenna
system. The other problem is keeping the feedline far enough away from
eveyerything else along that run, that could interact with it.

For such a long run with a feeder at ground-level, you might want to
investigate low-loss coax...

- Mike KI6PR
El Rancho R.F., CA

"DOUGLAS SNOWDEN" 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? 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?

Doug, N4IJ

Mikey wrote:
Balance woun't be the problem, Doug. The problem is that over that long a
run, the feedline will radiate, and become a major part of the antenna
system.

The reason that the feedline radiates *is* unbalanced currents.
If the currents can be balanced, the feedline will not radiate
appreciably assuming good engineering practices are followed.
--
73, Cecil, W5DXP

I saw an ariticle from a British ham that fed a vertical with open wire line,
mounted on his roof. Ground mounted might be problematic due to the fact that
the feedline could not be brought away at a preferred angle. Would be an
interesting experiment though!

73s,

Evan