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Author Topic: Ladder line  (Read 3534 times)
KJ6TSX
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Posts: 116




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« on: February 18, 2012, 09:19:10 PM »

Hi All
I am putting up a dipole with ladder line going from the antenna to my rig, what should I look out for?
is it OK to pass though metal air vents to get inside the building? and do I need clearance when going through sheetrock? how should I secure the ladder line to the building? or should I....
Thanks
George
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WB6BYU
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Posts: 13238




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« Reply #1 on: February 18, 2012, 10:05:41 PM »

Clearance depends on your power level and the impedance at that point on the feedline.

If the SWR on a 600 ohm feedline is 20 : 1, you can have 1500V peak across it at some
point(s) with just 100 watts output.  At other points along the line, or with a different load
impedance, it will be much lower.  If the SWR is reasonably low the peak voltage might
not exceed 500V.  That's what makes it difficult to make general recommendations - a lot
of hams can get by with cutting corners in their specific installation, but that might not
work in other cases.

Any insulators designed for electric fences are probably adequate for ham feedlines, certainly
at the 100W level.  Ordinary AC wiring usually is rated for 600V, so may be adequate in some
installations but not in others.  I've run feedline in through the holes in the screen over a
vent with no arcing, though the antenna was a full wave loop so the impedance was pretty
tame on all bands.  In most cases running an insulated wire through a piece of PEX pipe as
an insulator will be adequate at 100W, or using some of the insulated tubing sold to run
electric fence wires along the ground around a gate.  (You may have to cut out a couple
wires in the screen to make the holes large enough to fit the insulator.)  Teflon is also a good
insulator - either a length of tubing or some wraps of pipe tape in strategic places.

You can use the same approach with sheetrock.  I'm the sort who would just drill two holes
and pass the wires through, though it is always good idea to test for arcing and check the line
periodically for any signs of problems. 


Running ladder line near metal objects introduces impedance bumps in the line, but that
usually isn't a problem in typical ham use because the lines are usually operated as tuned
lines rather than being carefully matched at the load.  If one of the wires runs closer to
some metal than the other, especially over a significant distance, then the line can become
unbalanced, but crossing a vent or a metal downspout at a right angle doesn't affect the
line very much.
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KI8BL
Member

Posts: 22




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« Reply #2 on: February 19, 2012, 04:39:38 PM »

Clearance depends on your power level and the impedance at that point on the feedline.

If the SWR on a 600 ohm feedline is 20 : 1, you can have 1500V peak across it at some
point(s) with just 100 watts output.  At other points along the line, or with a different load
impedance, it will be much lower.  If the SWR is reasonably low the peak voltage might
not exceed 500V.  That's what makes it difficult to make general recommendations - a lot
of hams can get by with cutting corners in their specific installation, but that might not
work in other cases.

Any insulators designed for electric fences are probably adequate for ham feedlines, certainly
at the 100W level.  Ordinary AC wiring usually is rated for 600V, so may be adequate in some
installations but not in others.  I've run feedline in through the holes in the screen over a
vent with no arcing, though the antenna was a full wave loop so the impedance was pretty
tame on all bands.  In most cases running an insulated wire through a piece of PEX pipe as
an insulator will be adequate at 100W, or using some of the insulated tubing sold to run
electric fence wires along the ground around a gate.  (You may have to cut out a couple
wires in the screen to make the holes large enough to fit the insulator.)  Teflon is also a good
insulator - either a length of tubing or some wraps of pipe tape in strategic places.

You can use the same approach with sheetrock.  I'm the sort who would just drill two holes
and pass the wires through, though it is always good idea to test for arcing and check the line
periodically for any signs of problems. 


Running ladder line near metal objects introduces impedance bumps in the line, but that
usually isn't a problem in typical ham use because the lines are usually operated as tuned
lines rather than being carefully matched at the load.  If one of the wires runs closer to
some metal than the other, especially over a significant distance, then the line can become
unbalanced, but crossing a vent or a metal downspout at a right angle doesn't affect the
line very much.

True all he said,now also make sure you have a antenna tuner,for balanced lines!!!! you should be good. ladder line is better on feeding antennas.. most of your power out gets to the antenna
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W8AAZ
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Posts: 341




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« Reply #3 on: February 19, 2012, 07:45:40 PM »

Every ham should own one ARRL Radio Amateurs handbook. A cheap used copy, even. Even if it is not the most current, that is OK, ladder line has not really changed, in say, 90 years?  They give lots of feedline advice in there.  I am just thinkin', try to keep it away from metal as much as possible. Use insulated standoffs of some sort, if need be, to keep it away from metal and structures.  It is super low loss and excellent feedline if implemented correctly.  If the requirements for it's use are impractical, you might end up with using coax, or coax and a remote autotuner or such with it.
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KJ6TSX
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Posts: 116




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« Reply #4 on: February 19, 2012, 09:36:22 PM »

Thanks For all the help
The antenna went up without a hitch, used some heavy vinyl tubing to act as a chase were it went through the metal vent. when I switch between my old antenna and my new antenna the signal strength meter jumps from 3 to 5.
Haven't got to talk to anyone yet
Thanks again for the help
George
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K0ZN
Member

Posts: 1547




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« Reply #5 on: February 19, 2012, 09:57:59 PM »

Hi.

It is not real clear how you are going "through the metal vent".   Bottomline: ladderline should be kept a fair distance away from metal objects. If you are just penetrating
a single layer of sheet metal, the best situation would be to have the ladderline in a hole that is at least a couple of inches BIGGER than the ladderline. But, this is a hobby
and you do what you are sometimes forced to do, even if it is not the best practice. Again, it was not clear from your post...... I hope you are NOT running the ladderline
in a sheetmetal pipe or HVAC vent. It may "work", but that is a worst case....running ladderline inside a conductor.  You absolutely do NOT want the ladderline to
lay on something like sheetmetal or run parallel to it for significant distance unless it is held several inches away from it. I would say 6" is a minimum and 12" is better.
When you put some large piece of metal next to ladderline, it is like connecting capacitors across the line to short it !  That is why you want to keep it a fair distance from metal objects that are parallel to it; they capacitively couple to the line. "Not good."

Keep in mind, that ladderline (and all other parallel transmission lines) do not operate like coax. With coax, the energy is INSIDE the line. With ladderline, the energy
is AROUND the line. BIG difference. This is also why you absolutely do not want to coil up or leave any "extra" ladderline in a rats nest on the floor. It throws the
line out of balance and may couple to other cables and wires in the area. Keep a run of ladderline "clean" and cut to length.

There are some other posts on here recently about this same general subject. Check those out too.

 FYI:  I use that same antenna at my QTH. An 80 M dipole, fed in the center with ladderline. I built a small 6" X 6" plexiglass "window" in the side of the house for the ladderline entrance. I just cut a slot the size of the line in the plexiglass and bring the line in through that. This avoids ALL contact or proximity to any metal. The line
comes through that window, is suspended from the basement ceiling and comes to the Tuner. Works like a champ on all bands from 80 M up.

73,  K0ZN
« Last Edit: February 19, 2012, 10:02:36 PM by K0ZN » Logged
KJ6TSX
Member

Posts: 116




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« Reply #6 on: February 20, 2012, 08:31:35 PM »

I installed the ladder line though the vent screen that vents under the stairs that leads to my shack, just a 6 x 12 piece of 1/4 inch chicken wire, I sleeved the ladder wire with 1-1/4 plastic tubing about 12 inches long.
 My SWR seems high I can't seem to bring it down, I am using a MFG 949e tuner and no matter which inductor I use it stays at 1:1.75. The tuner is connected to a Kenwood ts-130s. I have found that when I get the SWR down my power output from the transmitter increases.
Kenwood on this model is supposed to have a safety device that lowers the power when there is high SWR to prevent damage to the output transistors. So getting the SWR down means more output two ways.
Any suggestions would be appreciated
Thanks
George
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WB6BYU
Member

Posts: 13238




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« Reply #7 on: February 20, 2012, 09:04:51 PM »

Quote from: KJ6TSX
... My SWR seems high I can't seem to bring it down, I am using a MFG 949e tuner and no matter which inductor I use it stays at 1:1.75...


Does your SWR change when you rotate the capacitors?

I presume you have the ladder line connected to the balun terminals on the rear panel with the
jumper connected to the single wire output terminal
.

What band are you trying to match the antenna on?

There can be a fair bit of fussing with the controls for minimum SWR - back and forth
between the capacitors.  Usually I look for a match with one or the other capacitor at
full capacitance (plates fully meshed) if possible - it often is.  That should give the
best efficiency. 

I have the older 949C tuner and the balun should match most impedances you are likely
to encounter with a reasonable antenna and feedline (though not all).  What antenna are
you using and how long is the feedline?  We can estimate the impedance seen by the
tuner.

Also, make sure that the antenna switch knob hasn't shifted on the shaft - you're switch
may be in the dummy load position when you think it is connected to the antenna.

Oh, and one more thing.  SWR is always given as the ratio of a larger number to one.  So
you would write it as 1.75 : 1.
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KJ6TSX
Member

Posts: 116




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« Reply #8 on: February 20, 2012, 09:51:45 PM »

Yep
I have the feedline connected to the two balanced line terminals and the wire between the line and one of the feedline pins.
The antenna is a Cobra Ultralite Kid with a total length of 41 feet with 40 feet of 1" ladder line. the antenna is mounted on the roof horizontally about 20 feet above the ground.
Thanks
George
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WX7G
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Posts: 6035




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« Reply #9 on: February 21, 2012, 05:28:46 AM »

Alternating between the two capacitor settings on a tuner will often not result in a 1:1 VSWR. When you get the VSWR as low as it will go, offset one cap 5 or 10 degrees to the right or the left. Now tune the other cap.

As you said your TS-130 increases power as the VSWR decreases. Once you get the VSWR down to as low as it will go continue to adjust the the capacitors for maximum PA current on the TS-130. Now the tuning is in reference to the TS-130 metering and not the tuner metering.
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K0ZN
Member

Posts: 1547




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« Reply #10 on: February 21, 2012, 06:58:07 PM »


Agree with WX7G.  You probably can get a 1:1 match, but it takes some patience and trying.  Also, note that the control settings at which create 1:1 will vary
DRASTICALLY between bands, and may change fairly significantly even from one end of 40M from the other.

I would take WX7G's good suggestion farther; if you need to turn ONE cap 50% away from the setting (either way) and "tweak" the Inductor and other cap
until you find a match. Just from past experience, it seems that more times than not, the "transmitter" control should be set to or near maximum CAPACITANCE.....
then "mess with" the Inductor and other cap.

As a completely Wild Guess, I would say you probably want the inductor set between about 30 to 50% of the available inductance on 40 M....and the required
inductance will decrease to nearly the smallest amount on 10 M. On 15, 12 and 10 M it is likely that the tuning controls will be very "sharp".

With a tuner like that you have 3 controls that you need to adjust to get a match....it can be a little frustrating. PATIENCE.  In finding the initial settings, the only thing you are really concerned with is Minimum REFLECTED power, regardless of the transmitter output....you are trying to get the match to a 1:1 RATIO. Power from the transmitter can be increased after you get the best SWR.  Be sure to WRITE the settings down when you find them !!

Often, you can get "into the ball park" just by listening to the noise in the receiver. Turn the RF gain down some and "play" with the tuner controls, tuning for
maximum background noise out of the receiver. The position of the capacitor controls may go from one extreme to another....i.e. the settings that give a match
and 1:1 SWR could be anywhere, so to speak. I have never used that Tuner, but as a guess, typically, I would start out with the capacitors about 1/2 meshed....
or at "50%" setting....then vary the inductor for lowest SWR or LOUDEST noise....then turn the capacitors EITHER direction to see what happens. The point of
match may be very sharp and you can pass over it fairly easily. There should be some basic guidelines in the Owner's Manual. If you fail to get a match on
40M, try 20M...often the tuners will have more range on 20 M. Since that tuner does not have a roller inductor, it is not impossible that you find a situation where
you cannot get 1:1 because you cannot infinitely vary the inductance, but with some patience, the odds favor finding a match of 1:1 in most cases.

If you find you absolutely cannot get a match on one band, you probably will need to add about 1/8 to 1/4 wavelength of ladderline. DO NOT coil up or leave any
extra line in a rats nest. Keep it neat and spaced from itself.

Respectfully:  The absolute best investment you can make in your station at this point is to pick up a copy of the ARRL Antenna Book and do some studying on
antenna fundamentals. Antennas are not complex, but they are not forgiving of errors either. The time and effort you put in picking up knowledge on antenna
basics and transmission line basics will pay itself back many times over with reduced frustration, more fun and a stronger signal. The cold reality is that this is a technical hobby; there is no way around it. "Knowledge is Power" !

73
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WA9YSD
Member

Posts: 138




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« Reply #11 on: February 22, 2012, 10:15:15 AM »

If you have to run open line through or around metal objects, take 2 pieces of coax like RG-213 run them parallel. Connect shields together on both ends ground the shields on one end. Connect feed line to the center conductors.

Jim, K9TF
« Last Edit: February 22, 2012, 10:50:22 AM by WA9YSD » Logged
WB6BYU
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Posts: 13238




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« Reply #12 on: February 22, 2012, 10:34:29 AM »

Quote from: KJ6TSX

The antenna is a Cobra Ultralite Kid with a total length of 41 feet with 40 feet of 1" ladder line...



What bands are you trying to match it on?  Shouldn't be too bad on 10 - 20m, and perhaps 30m.
It may be inefficient on 40m, but the losses might put the impedance in a range that the tuner
can handle (depending on the line length.)  Even the high losses on 80m might not be enough
to help on that band.
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WA9YSD
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Posts: 138




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« Reply #13 on: February 22, 2012, 10:42:12 AM »

Not the Cobra! Wave cancelations remember?

Jim K9TF
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KJ6TSX
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Posts: 116




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« Reply #14 on: February 22, 2012, 07:55:01 PM »

Well I finally got it to tune in, All the advise paid off!!!
Jim K9TF wrote
Quote
Not the Cobra! Wave cancelations remember?
What do you mean??
Thanks
George
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