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

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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Thanks for all the feedback. As for running 275 ft of RG58, I would not do
that, but would try something like 9913 or LMR400, etc. The only reason I
am considering open wire feeders is to get ever watt to the antenna, and
save the cost of good coax. As for the comment that the feedline would be
part of the antenna at that long of a run, that was part of the original
post, and my worrying about the antenna intself unbalancing the feedline.
The way I understand it, the feedline should not radiate or be part of the
antenna if it is balanced. At least I know others are doing this with
success. I don't know if I would want to go to the trouble of making a three
wire open wire feeder.
As for the interaction of other things with the feeline, there is nothing
except open field for the distance.


Doug N4IJ



"K9SQG" wrote in message
...
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

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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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

Doug, N4IJ, wrote:

... As for the comment that the feedline would be
part of the antenna at that long of a run, that
was part of the original post, and my worrying
about the antenna intself unbalancing the feedline.
The way I understand it, the feedline should not
radiate or be part of the antenna if it is balanced.

I think that given the length of your run (275 ft) and
the use of close-spaced commercial "window line", any
common-mode problems on the line would sort themselves
out before they got back to your shack. Giving the
line a relatively tight twist (1 twist/6 inches) might
help too.

Given that you intend to drive a relatively non-directional
antenna, I don't think feedline radiation will be a big
problem system-wise if it is 1/10 the total radiated power.
(ie: suppressed 10 dB).

Nobody wants to take me up on the unbalanced ladder-line.
Oh, well!

Jim, K7JEB
Glendale, AZ

K7JEB wrote:
Nobody wants to take me up on the unbalanced ladder-line.
Oh, well!

Hi Jim,
I'm thinking it has a distinct advantage over balanced ladder-
line. It appears to me that it can be formed into a helix
where the outside insulated wires are touching without suffering
the ill effects of balanced ladder-line. This is interesting to
me because I vary the length of the ladder-line to achieve
a match. Now if it could only be coiled up in a box like
coax.
--
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
..

"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?

It has twice the loss.

Tam/WB2TT

I show it or regular rg-8 to have only about .2 db more loss per 100
ft than foam rg-8. "10 mhz" So 275 ft would be appx 2.1-2.2 or so db
vs the 1.5 db. I would consider twice the loss to be 3 db loss.
..6 db should be hardly noticable. MK

"Mark Keith" wrote in message
om...
"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?

It has twice the loss.

Tam/WB2TT

I show it or regular rg-8 to have only about .2 db more loss per 100
ft than foam rg-8. "10 mhz" So 275 ft would be appx 2.1-2.2 or so db
vs the 1.5 db. I would consider twice the loss to be 3 db loss.
.6 db should be hardly noticable. MK

My chart shows the following loss at 10 MHz:, per 100 feet

RG213 0.8db
RG8 Foam 0.55 db
9913 0.4 db

LMR400 will be marginally better than 9913. By definitin of db, 1 db is the
smallest change that is detected by the human ear. 6db is a factor of 4 in
power. By twice the loss I meant twice the number of db.

This may all be moot, because he is going to have a horrendous SWR on at
least one of the bands. I would install two resonant radiators, or some kind
of decoupling stubs like the Hygain HT.

Tam/WB2TT

Tarmo Tammaru wrote:
This may all be moot, because he is going to have a horrendous SWR on at
least one of the bands. I would install two resonant radiators, or some kind
of decoupling stubs like the Hygain HT.

I would use a loading coil on 75m and short it out for 40m.
--
73, Cecil, W5DXP

"Cecil Moore" wrote in message
...
Tarmo Tammaru wrote:
This may all be moot, because he is going to have a horrendous SWR on at
least one of the bands. I would install two resonant radiators, or some
kind
of decoupling stubs like the Hygain HT.

I would use a loading coil on 75m and short it out for 40m.
--
73, Cecil, W5DXP

That works, or how about a 40m trap to keep it automatic.

Tam/WB2TT

Tarmo Tammaru wrote:
That works, or how about a 40m trap to keep it automatic.

66 ft tall vertical broken in the middle? OK, I guess ...
--
73, Cecil http://www.qsl.net/w5dxp



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