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OT: Balanced Feedlines

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Don Rasmussen

OT: Balanced Feedlines

Can anyone suggest a compact balanced line that can handle 1000 watts? I like the size of that Radio Shack 300 ohm TV line, but 100 watts is likely the maximum. I'd like to build a stealthy KW antenna. The 20m dipole radiating elements are so low to the ground that 3:1 SWR is the best I can get. If I tune this out with a tuner, there will be too many db's of loss over the 100 feet of feed required. I assume a KW would melt the TV line. Any suggestions? Don...
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Vic K2VCO

Re: OT: Balanced Feedlines

Don Rasmussen wrote:
> Can anyone suggest a compact balanced line that can handle 1000 watts? I like the size
> of that Radio Shack 300 ohm TV line, but 100 watts is likely the maximum. I'd like to
> build a stealthy KW antenna. The 20m dipole radiating elements are so low to the ground
> that 3:1 SWR is the best I can get. If I tune this out with a tuner, there will be too
> many db's of loss over the 100 feet of feed required. I assume a KW would melt the TV
> line. Any suggestions? Don...

DX Engineering has a 300-ohm line that might fill the bill.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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Augie "Gus" Hansen

Re: OT: Balanced Feedlines

In reply to this post by Don Rasmussen

Don Rasmussen wrote:
> Can anyone suggest a compact balanced line that can handle 1000 watts? I like the size of that Radio Shack 300 ohm TV line, but 100 watts is likely the maximum. I'd like to build a stealthy KW antenna. The 20m dipole radiating elements are so low to the ground that 3:1 SWR is the best I can get. If I tune this out with a tuner, there will be too many db's of loss over the 100 feet of feed required. I assume a KW would melt the TV line. Any suggestions?

DX Engineering (and other sources) sell 300-ohm window line, which
easily handles 1KW. It is better for TX use than the RS stuff that is
primarily used for receiving applications. I have used the window line
for years for an 80-10 meter doublet without problems. When the line
gets wet minor retuning may be required, and loss is greater than that
of true open-wire feedline.

Gus Hansen
KB0YH

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list1

Re: OT: Balanced Feedlines

In reply to this post by Don Rasmussen

Hi Don and All,

I don't know if 300 Ohm ladder line is small enough for you, but at 20:1 SWR
100 feet of it loses about 1.1 dB total. See the chart for 450 Ohm line at
the center of this page:
http://tinyurl.com/m5rjww

The loss for 100 feet of 450 Ohm line at 20:1 SWR is about .65 dB total. I
had calculated that the loss of 300 Ohm line in a similar situation is about
.5 dB worse. The 300 Ohm is really hard to see when put up. I used it for
Field Day, see:
http://tinyurl.com/luwagy

At the Wireman web site it describes its "562" 300 Ohm ladder line as being
able to take full power.
"300 ohm, 18 AWG, 19 strand copper-clad steel conductors, poly-clad 'window'
for full power VF .91"

The Wireman is at:
http://tinyurl.com/mdkvtm

73,
Steve, W2MY, AAR6CX

-----Original Message-----
Behalf Of Don Rasmussen
Subject: [Elecraft] OT: Balanced Feedlines

Can anyone suggest a compact balanced line that can handle 1000 watts? I
like the size of that Radio Shack 300 ohm TV line, but 100 watts is likely
the maximum. I'd like to build a stealthy KW antenna. The 20m dipole
radiating elements are so low to the ground that 3:1 SWR is the best I can
get. If I tune this out with a tuner, there will be too many db's of loss
over the 100 feet of feed required. I assume a KW would melt the TV line.
Any suggestions? Don...

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Joe Planisky

Re: OT: Balanced Feedlines

In reply to this post by Don Rasmussen

I know it doesn't answer the question you asked, but RG-8/RG-213 has a
loss of about 0.85 dB/100 ft at 20m. Your 3:1 SWR will add a little
less than 0.4 dB additional loss for a total loss of 1.25 dB. Is the
added hassle of running balanced line worth the extra 1.1 dB? Are
there other reasons you want to use balanced line?

73
--
Joe KB8AP

On Jul 16, 2009, at 5:39 PM, Don Rasmussen wrote:

>
> Can anyone suggest a compact balanced line that can handle 1000
> watts? I like the size of that Radio Shack 300 ohm TV line, but 100
> watts is likely the maximum. I'd like to build a stealthy KW
> antenna. The 20m dipole radiating elements are so low to the ground
> that 3:1 SWR is the best I can get. If I tune this out with a tuner,
> there will be too many db's of loss over the 100 feet of feed
> required. I assume a KW would melt the TV line. Any suggestions?
> Don...
> ______________________________________________________________
> Elecraft mailing list
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w7aqk

Re: OT: Balanced Feedlines

In reply to this post by list1

I've been using 300 ohm stuff from the Wireman for several years now. I
bought a 500 ft. roll of it, and have never regretted it. It has small
"windows", like 450 ohm line does, so it doesn't act like a sail when it's
in the air. I believe the difference in loss is negligible compared to 450
ohm line, and it is so much easier to work with. FWIW, I recommend it.

Dave W7AQK

----- Original Message -----
From: "list1" <[hidden email]>
To: <[hidden email]>
Sent: Thursday, July 16, 2009 6:09 PM
Subject: Re: [Elecraft] OT: Balanced Feedlines

> Hi Don and All,
>
> I don't know if 300 Ohm ladder line is small enough for you, but at 20:1
> SWR
> 100 feet of it loses about 1.1 dB total. See the chart for 450 Ohm line
> at
> the center of this page:
> http://tinyurl.com/m5rjww
>
> The loss for 100 feet of 450 Ohm line at 20:1 SWR is about .65 dB total.
> I
> had calculated that the loss of 300 Ohm line in a similar situation is
> about
> .5 dB worse. The 300 Ohm is really hard to see when put up. I used it
> for
> Field Day, see:
> http://tinyurl.com/luwagy
>
> At the Wireman web site it describes its "562" 300 Ohm ladder line as
> being
> able to take full power.
> "300 ohm, 18 AWG, 19 strand copper-clad steel conductors, poly-clad
> 'window'
> for full power VF .91"
>
> The Wireman is at:
> http://tinyurl.com/mdkvtm
>
>
> 73,
> Steve, W2MY, AAR6CX
>
>
> -----Original Message-----
> Behalf Of Don Rasmussen
> Subject: [Elecraft] OT: Balanced Feedlines
>
> Can anyone suggest a compact balanced line that can handle 1000 watts? I
> like the size of that Radio Shack 300 ohm TV line, but 100 watts is likely
> the maximum. I'd like to build a stealthy KW antenna. The 20m dipole
> radiating elements are so low to the ground that 3:1 SWR is the best I can
> get. If I tune this out with a tuner, there will be too many db's of loss
> over the 100 feet of feed required. I assume a KW would melt the TV line.
> Any suggestions? Don...
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

Geoffrey Mackenzie-Kennedy

Re: OT: Balanced Feedlines

In reply to this post by Joe Planisky

Joe,

Forgetting about RF performance for a moment, wouldn't the weight of RG-8/
RG-213 create a problem unless the antenna is supported at its feedpoint ?
If it is not supported, Don could end up with an inverted inverted V, aka a
"Droopy Dipole".

BTW I do not use the plastic window/ ladder line stuff here because we get a
lot of rain and use 4 wire open wire line for long runs, which is a hassle
to build but which has very low loss at HF and VHF wet or dry.

73,
Geoff
GM4ESD

Joe Planisky wrote on Friday, July 17, 2009 2:20 AM

>I know it doesn't answer the question you asked, but RG-8/RG-213 has a
> loss of about 0.85 dB/100 ft at 20m. Your 3:1 SWR will add a little
> less than 0.4 dB additional loss for a total loss of 1.25 dB. Is the
> added hassle of running balanced line worth the extra 1.1 dB? Are
> there other reasons you want to use balanced line?
>
> 73
> --
> Joe KB8AP

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Jim Brown-10

Big Coax on Dipoles

On Fri, 17 Jul 2009 09:19:03 +0100, Geoffrey Mackenzie-Kennedy wrote:

>orgetting about RF performance for a moment, wouldn't the weight of RG-8/
>RG-213 create a problem unless the antenna is supported at its feedpoint ?

I have four fan dipoles suspended at 100-120 ft between tall trees
(redwoods), all fed with RG8 or RG11. There is no problem supporting the big
coax. The keys to success are robust mechanical construction so that you can
establish high lateral tension. If one of the objects you're suspending from
is a tree, one end needs a weight and pulley to adjust to wind conditions. I
use 6.5 gallon water jugs filled with dry sand (roughly 95 pounds), and the
trees are typically 140-220 ft apart. I use 5/16-inch dual woven poly rope,
#10 solid copper, and robust insulators. Do they sag? Sure -- at least 10 ft
on the long dipoles. Does it matter? No.

One of the side benefits of the big coax is that my 80/40 fans (at right
angles) work quite well on 30M, 17M, 12M, and 6M, thanks to the lower loss
with moderate degrees of mismatch. With relatively litte time on 6M, I've
made nearly two dozen QSOs of more than 2,500 miles with my K3 and one of
those dipoles.

73,

Jim Brown K9YC

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Geoffrey Mackenzie-Kennedy

Re: Big Coax on Dipoles

Good morning Jim,

Thanks for your e-mail. I also use tall trees to support antenna catenarys,
which are made from 6mm dia woven marine rope, along with marine pulleys,
and a counterweight at one end of each catenary. The counterweight for each
catenarys is "fused", so if another tall tree falls across a catenary or
antenna during a storm, the catenary/ antenna will come down under the tree
without serious damage, and the rope will still be running through the
support pulley which makes it easy to hoist again after the fallen tree is
removed.

At one time I used airborne coax feeders here but replaced them with open
wire feeders, after somebody shooting pheasant on the farm filled a coax
feeder with lead shot.

73,
Geoff
GM4ESD

On Wednesday, July 22, 2009 at 6:03 AM, Jim Brown wrote:

> I have four fan dipoles suspended at 100-120 ft between tall trees
> (redwoods), all fed with RG8 or RG11. There is no problem supporting the
> big
> coax. The keys to success are robust mechanical construction so that you
> can
> establish high lateral tension. If one of the objects you're suspending
> from
> is a tree, one end needs a weight and pulley to adjust to wind conditions.
> I
> use 6.5 gallon water jugs filled with dry sand (roughly 95 pounds), and
> the
> trees are typically 140-220 ft apart. I use 5/16-inch dual woven poly
> rope,
> #10 solid copper, and robust insulators. Do they sag? Sure -- at least 10
> ft
> on the long dipoles. Does it matter? No.
>
> One of the side benefits of the big coax is that my 80/40 fans (at right
> angles) work quite well on 30M, 17M, 12M, and 6M, thanks to the lower loss
> with moderate degrees of mismatch. With relatively litte time on 6M, I've
> made nearly two dozen QSOs of more than 2,500 miles with my K3 and one of
> those dipoles.
>
> 73,
>
> Jim Brown K9YC

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Steve Ellington

Re: Big Coax on Dipoles

In reply to this post by Jim Brown-10

The feed point on some of those bands would see a 150:1 swr (no kidding)!
Your efficiency would be about 5%. Your tuner would still see a low swr and
it will be an easy match because of the tremendous loss in that 100 pounds
of coax. Sure you can work stations, with that height you could QSO with a
light bulb, but you would be 100 times stronger using ladder line plus you
wouldn't need 95 pounds of sand to hold up that lossy dummy load coax.
I'm feeding a 200' doublet with ladder line then to a 4:1 current balun next
to the K3. The K3's internal tuner finds a match on 160-6 meters and I have
very little power loss on any band. Now if I could just find a fertilizer to
make my tree grow another 50'!

Steve
N4LQ
[hidden email]
----- Original Message -----
From: "Jim Brown" <[hidden email]>
To: "Elecraft List" <[hidden email]>
Sent: Wednesday, July 22, 2009 1:03 AM
Subject: [Elecraft] Big Coax on Dipoles

> On Fri, 17 Jul 2009 09:19:03 +0100, Geoffrey Mackenzie-Kennedy wrote:
>
>>orgetting about RF performance for a moment, wouldn't the weight of RG-8/
>>RG-213 create a problem unless the antenna is supported at its feedpoint ?
>
> I have four fan dipoles suspended at 100-120 ft between tall trees
> (redwoods), all fed with RG8 or RG11. There is no problem supporting the
> big
> coax. The keys to success are robust mechanical construction so that you
> can
> establish high lateral tension. If one of the objects you're suspending
> from
> is a tree, one end needs a weight and pulley to adjust to wind conditions.
> I
> use 6.5 gallon water jugs filled with dry sand (roughly 95 pounds), and
> the
> trees are typically 140-220 ft apart. I use 5/16-inch dual woven poly
> rope,
> #10 solid copper, and robust insulators. Do they sag? Sure -- at least 10
> ft
> on the long dipoles. Does it matter? No.
>
> One of the side benefits of the big coax is that my 80/40 fans (at right
> angles) work quite well on 30M, 17M, 12M, and 6M, thanks to the lower loss
> with moderate degrees of mismatch. With relatively litte time on 6M, I've
> made nearly two dozen QSOs of more than 2,500 miles with my K3 and one of
> those dipoles.
>
> 73,
>
> Jim Brown K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

n7ws

Re: Big Coax on Dipoles

In reply to this post by Jim Brown-10

Re: 150:1 SWR.

I have an inverted vee style dipole consisting of two wires fed in parallel at the feed-point, one cut for 80/75 (depending on some jumpers at the ends) and the other for 40-meters. The feed is at about 45 feet above ground and the low-freq dipole ends are at about 25' above ground. The wires are displaced horizontally (fanned) about 25 degrees from each other.

I have a pretty accurate model of this antenna, that has be confirmed against actual measurements on the two bands using my N2PK vector network analyzer that was calibrated at the end of a 50' run of cable necessary to get from the antenna to ground.

The tower is about 125' from the shack so the total run of RG-213 is about 200'.

The modeled worst case SWR occurs on 20-meters where it is about 32:1. Including the transmission line loss decreases the SWR to under 5:1 over all of the ham bands from 80 thru 6 meters, with the worst case still being 20-meters. The worst case line loss is a bit over 8 dB, with 20 and 10-meters being the culprits.

Since I have a HB three-element Yagi for 20, that band is not an issue and I can work all of the other HF bands using only my L4-B "active tuner". I've also worked about 120 Q's on 6-meters using the K3 (no tuner) and have about 20 states worked and 5 DXCC countries, including a couple of JAs on that band using the same antenna.

(Editorial mode on: The JAs were worked on Field Day and I worked them about an hour apart. The first one was still calling CQ without success when I worked the second. So the band was open for DX but no one (except me) was listening.)

However, this is in no way an endorsement of using such a system as an all-band antenna, even one fed with ladder line. These antennas are at best compromises, with generally unknown performance characteristcs, and at worst not much better than dumy loads.

Wes Stewart N7WS

--- On Wed, 7/22/09, Steve Ellington <[hidden email]> wrote:

From: Steve Ellington <[hidden email]>
Subject: Re: [Elecraft] Big Coax on Dipoles
To: "Jim Brown" <[hidden email]>, "Elecraft List" <[hidden email]>
Date: Wednesday, July 22, 2009, 7:57 AM

The feed point on some of those bands would see a 150:1 swr (no kidding)!
Your efficiency would be about 5%. Your tuner would still see a low swr and
it will be an easy match because of the tremendous loss in that 100 pounds
of coax. Sure you can work stations, with that height you could QSO with a
light bulb, but you would be 100 times stronger using ladder line plus you
wouldn't need 95 pounds of sand to hold up that lossy dummy load coax.
I'm feeding a 200' doublet with ladder line then to a 4:1 current balun next
to the K3. The K3's internal tuner finds a match on 160-6 meters and I have
very little power loss on any band. Now if I could just find a fertilizer to
make my tree grow another 50'!

Steve
N4LQ
[hidden email]
----- Original Message -----
From: "Jim Brown" <[hidden email]>
To: "Elecraft List" <[hidden email]>
Sent: Wednesday, July 22, 2009 1:03 AM
Subject: [Elecraft] Big Coax on Dipoles

______________________________________________________________

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