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Coax or Ladderline for your antenna system??




 
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Author Topic: Coax or Ladderline for your antenna system??  (Read 20310 times)
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ka2zni
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« on: October 24, 2007, 08:03:41 PM »

Here's a recent disussion I ran into and thought I would pass it on as a question:

What type of feedline do you use and why?? Coax? Ladderline? Homemade?

I found the subject rather interesting and have found a ton of topics on the internet, Everyone has their reasons, what works for you and why??

I have tried both this week.... Some interesting results to follow...........


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WA1GFZ
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« Reply #1 on: October 24, 2007, 09:40:03 PM »

#10 spaced 4 inches with Johnson spreaders. 250 foot dipole.
I prefer coax on the LPDA  gfz
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Ed-VA3ES
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« Reply #2 on: October 24, 2007, 11:03:40 PM »

I use balanced line (450 ohm Ladder-line) on my multi-band doublets.  I use coax on my yagis and  verticals.
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« Reply #3 on: October 25, 2007, 12:11:57 AM »

I use 14 ga stranded 450 ohm ladderline with my 260' flat top dipole, but would like to switch to homebrew 600 ohm open wire feeders with about a 6" spacing. To me, the open wire feeders are the optimum feedline.

Whatever you do, try to keep everything "balanced", including a double balanced antenna tuner.

My tuner: http://members.aol.com/yardleyite/tuner.html

Just my two cents worth.........

Regards,
           Joe Cro N3IBX
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Joe Cro N3IBX

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« Reply #4 on: October 25, 2007, 01:09:01 AM »

I swear by 600 ohm open-wire transmission line. On a gamble a few years back, I bought the stuff that W7FG offers, and I have found it to be reliable, inexpensive, easy to work with, and it holds up well. Other users report similar positive experiences. Regardless of rain or snow, the impedance of this line remains essentially constant, unlike the 450 ohm glorified TV twin-lead. The only time I have to tweak the antenna matching network (other than when I QSY), is when there is appreciable ice build-up on the antenna and/or feedline. I would recommend the W7FG product to anyone, and it beats the hassle of having to fabricate 600 ohm open wire feeders yourself. It is also very lightweight, so it reduces the sag and loading on the span of a fairly long wire antenna.

I feed my 126' flat-top antenna/open-wire transmission line combination with a homebrew balanced-L network. Works great, and I can maintain a unity VSWR anywhere from 3.5 Mhz to the high end of the 10 meter band with no problem.

The only drawback to open-wire feeders is the need to achieve electrical balance in the line and antenna; this is  accomplished by maintaining the best possible physical symmetry in the installation, and by feeding the line with a source that provides nearly perfect balance between the two phases. I think that a balanced L-network can achieve this best. The routing of the feedline is critical in that it must be kept away (by at least 18 inches) from metallic structures, and like any type of feedline, should be run ideally at a right angle from the antenna proper.

As Mikey says, "Try it, you'll like it!".

73,

Bruce
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« Reply #5 on: October 25, 2007, 08:32:01 AM »

^^  Second what Bruce sez.  The W7FG stuff is absolutely outstanding, is dirt cheap for what it is, converting to that from coass was the single biggest improvement I ever made to my station.

I have two 75 M flat tops fed with this stuff (one a fan dipole) and although the end ropes have broken, the W7FG has NEVER failed and handles high power with no problem at all.

To feed it into the shack I cut a piece of plexiglas to fit in the window, installed a could of banana jacks for "feedthrus", and just closed the window on the plexiglas.

Considering the time and materials you could never begin to make that feedline for what W7FG charges for the stuff.
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The Slab Bacon
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« Reply #6 on: October 25, 2007, 08:45:04 AM »

Coax is fine for beams and verticals, but I would never consider anything but ladder line for feeding a balanced antenna (Dipole, inverted V, etc.) It just works so much better and enables easy multi band operation with a good tuna. Just be sure to pick stuff with heavy enough conductors to keep the I/R losses to a minimum.

                                                The Slab Bacon
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Jim KF2SY
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« Reply #7 on: October 25, 2007, 09:06:00 AM »


I use 14ga. 450 ohm ladderline (from Davis RF)
on my ocf dipole for multi-band oper.
Virtually no wx related swr effects, as the ant. is insulated wire ;-)

Your mileage may vary...
tag, title tax, extra.
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Steve - WB3HUZ
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« Reply #8 on: October 25, 2007, 09:17:16 AM »

I've used both - coax and balanced open-wire. Both work the same, when used properly. The key thing is to make the length of your line, be it coax or open-wire, long enough to reach from your transmitter to your antenna. Wink

All kidding aside, it's all about tradeoffs. Coax is much simpler. There is no need to worry about nearby conductors, it is more easily passed through walls and such, rain and snow have no effect, and generally no tuner is needed. For this simplicity, you give up bandwidth (unless you use a tuner on a single band), there is no multiband capability (with exceptions like using a 40 meter dipole on 15 meters, etc), there is more loss in the line (only an issue on long runs), heavier line (may put more stress on the center of the dipole), and it is probably more expensive (generally coax is more expensive than ladder-line).

Open-wire feedline is a little more complex, mainly in that your need to use a tuner. I've never understood many people's seeming aversion to using a tuner since it is not much different than tuning a transmitter. Once you find the proper settings for each band, moving frequency/bands is pretty simple. But the added complexity gives you almost complete frequency independence/capability (given a proper tuner). This feature alone can be the best selling point for those who don't have space for multiple antennas.

Another thing to consider is a multiband coax-fed system of several dipoles. Here you have several dipoles, cut for various bands, on a common feedpoint. In this manner, you sort of get the best of both worlds, the simplicity of coax and multiband capability.

One final item in favor of open-wire feed is that you can use your 75 meter dipole on 160 meters. If you have space for a full-sized dipole on 160, this is not a big deal. But if you don't (and many don't, considering the amount of space needed), this is a BIG deal (no pun intended). The caveats are that you will need a good tuner - no parts can get hot when transmitting, so you will need a coil made of large conductor (copper tubing or similar) and preferably a higher-quality feedline. Ladder-line will work, but losses can be higher than desirable, especially on longer runs. So, something like open-wire line with larger conductor size (12 ga or larger) is preferred.

Good luck with your antenna project(s).
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W1UJR
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« Reply #9 on: October 25, 2007, 09:19:59 AM »

Hi Kevin,

There is not much more than I can add that the other illustrious folks before me have not shared, but I can relate a few of my experiences here at W1UJR.

First, W7FG line and antennas work great, they are inexpensive, and overall quite robust.
You'll see in the photo below that my location lacks any center support, and being fresh out of "skyhooks", I just let it dangle at the feedpoint.

The only problem I had with the stuff was a break near the lower feedpoint on the building.
This was caused by the antenna flexing in the wind, I mentioned the lack a center support, the wire "work hardened" and broke from fatigue. I simply cut and soldered it back together, liberally coated with self fusing tape for the repair. To prevent future problems I used the old loop and spring trick that is mentioned in the early ARRL handbooks. I can email a photo if that helps.

My feeling is that if you are not going to have multiple resonant antennas for each band, then balanced line is really the way to go. Yes its an old technology and a bit more of a challenge to run than coax, but it has low loss, works over a wide SWR, is inexpensive, and the coolest thing is that you can attach little neon bulbs to indicate your power level and balance. I use two of these at the feedpoint in the shack, and adjust for equal brilliance. The bulbs also flicker during keying, or modulation, serving as as very rough mod monitor.

I run my feedline through the barn siding using porcelain insulators and threaded rod, then down the inside wall, and connect to the Johnson Matchbox. I then use coax in the shack between the various RX and TX units.


W7FG Antenna and Feedline at W1UJR



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ve6pg
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« Reply #10 on: October 25, 2007, 10:45:26 AM »

...homebrew ladder line...spaced 5 inches...werks fb...i used 1/2 inch pvc pipe, cut at 6 inches...12 ga wire...never a problem....sk..
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« Reply #11 on: October 25, 2007, 11:24:23 AM »

Hey Joe,
How much L do you end up using on 160 with that tuner. I only have 22 uh inductors and could use a little more L. Todd KAQ will tell you my tuner is too ugly for pictures.  gfz
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« Reply #12 on: October 25, 2007, 11:39:21 AM »

I think that you should build a treehouse hamshack and bring the two ends right into the shack and attach them directly to the tuner

WU2D Mike  Cool
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flintstone mop
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« Reply #13 on: October 25, 2007, 11:52:10 AM »

Any of the ladder lines are so easy to get along with. No problems ever with the 450 ohm window line. Open ladder line can handle very high SWR without a tremendous amount of loss. Great for the untuned dipole and multiband use with a heavy duty low loss balanced tuner.
I cut a 2 inch hole through some 2X6 or 4X6 and used a PVC pipe to get the ladder line into the basement where the K1JJ tuner is mounted on the cinder block wall, about 5 feet from the hole.
Running open ladder line in through the basement across house wires and Flourescent fixtures, about 50 feet, caused major problems and a lot more noise pickup.
Fred
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« Reply #14 on: October 25, 2007, 12:23:32 PM »

I have never used coax to directly feed a dipole.  When I first started with my novice rig, I used 72-ohm TV twinlead.  It was about half the size of the smallest size zip cord, but it worked well - until I tried to run more than about 100 watts input.

Then I went to open wire line.  I have used a number of varieties, from the 450-ohm open wire TV  stuff (#18 copperweld with 1" plastic spreaders spaced every 6 inches or so), to homebrew using plexiglas rods, polystyrene rods and  ceramic spacers, with everything from 1" to 6" spacing. It all worked about the same for me, but the UV quickly disintegrated the polystyrene rods.

I prefer to put all my effort into one good solid dipole that will work multiple bands and work across any band with uniform efficiency, than to have a rat's nest of self-resonant dipoles strung all over the place, plus the separate dipoles can be expected to all interact to a certain extent. With the open wire line, I never worried about SWR - just tuned for maximum coupling to the transmitter and highest reading on the thermocouple rf ammeter.

My present dipole and open wire feeders are made of #10 copperweld, salvaged from abandoned telegraph lines that ran along the train tracks.  Part of it uses 2" Johnson ceramic spacers, and the part that goes up the tower uses a spacer made from a plexiglas strip, every 10 feet, running up inside the tower, with the spacers attached to tower rungs, and tension on the wires maintained with turnbuckles.  I use buried coax for the 140' run from the transmitter to the tuners at the  base of the tower, but have contemplated relocating the tuners in the shack and running open wire line all the way to the tower so I don't have to go out to the tower to change bands or make large excursions within a band.

I also use the same coax line to directly feed the 160m vertical through an L-network at the base of the tower.  Many older broadcast installations used 5-wire open wire feeders to simulate a coax line, which probably has lower loss than RG-213.

Even when feeding with coax, I don't worry too much about SWR if it is less than about 2.5:1.
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KA1ZGC
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« Reply #15 on: October 25, 2007, 01:02:26 PM »

The simple answer is: yes!  Wink

Using a balanced feed to a balanced ant gives you much more flexibility, as others have stated already. An open line can become part of the antenna in a way that coax can't.

That's not all there is to it, though; there's the question of how you arrive at a balanced feed, how your balanced line is run, and what kind of antenna you're feeding. Different scenarios call for different solutions.

Personally, I prefer to run coax from the shack to a link-coupled tuner at the feedpoint of a balanced line dropping straight down from the ant. This gives you several advantages: you can mitigate in-house RF issues like what Fred was describing, your balanced feedline can be one straight-down drop (so there are no parallel runs to cause imbalance), and you can dial in the perfect impedance transformation with the tuner (unlike a balun). The use of a link-coupled tuner also leaves your antenna floating for DC, which can be handy if your ant likes to take a charge from nearby lightning strikes.

On the downside, you need to take a walk to the ant to change bands, and are better off taking that same walk if you want to make a large band excursion.

My 200' flat-top is fed this way, with 35' of 420 ohm black window crap dropping straight down from the ant to the tuner. The tuner is fed by 120' of RG-11 (yes, I know that's 72 ohm line) straight from the transmitter.

With the tuner set for a flat match at 3885, I can still tune the transmitter for 3710 quite happily. The only caveat there is that if I don't retune the ant, impedance shifts caused by weather changes will manifest themselves at the transmitter much more readily than if I retune. I was on 3710 with the ant tuned for 3885 the other night when a quick passing shower caused my plate current to jump up 50 mA in 20 seconds. On that same frequency, with the ant properly tuned, there's hardly any weather-induced change at all.

In short, you're far better off with coax in your shack, and far better off with a balanced line feeding your ant (in most cases, depending on the ant). How you get from one to the other is up to you.

My $0.02.

--Thom
Keep Away One Zorched Ground Conductor
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Vortex Joe - N3IBX
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« Reply #16 on: October 25, 2007, 02:03:41 PM »

I think that you should build a treehouse hamshack and bring the two ends right into the shack and attach them directly to the tuner

WU2D Mike  Cool

Mike,
      Good thinking OM! The real trick is to figger out the right amount of open wire line, nix on the tuna, and toon out the reactance with your link coupled tank circut in your transmitter!

I can (fortunately) do that with some of my more oldbuzzardly rigs for 75M.

Best Regards and hope your treehouse/hamshack is a double balanced treehouse/hamshack!

Joe Cro N3IBX
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Joe Cro N3IBX

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« Reply #17 on: October 25, 2007, 02:17:19 PM »

I look forward to using open wire feeders someday, been amassing the insulators, feed thrus, and other hardware for years. The current location doesn't lend itself to it, between the radio room location, twists and turns to reach the antenna out back, metal standing seam roofing on a portion of the back roof and so on.

The good points have been made by others. Coax is easier and more practical in cases like mine, but if you have a clean shot from your radio room, go for the open wire. Along with enhanced utility, the coolness factor is very high.  Wink
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Vortex Joe - N3IBX
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« Reply #18 on: October 25, 2007, 02:21:48 PM »

Hey Joe,
How much L do you end up using on 160 with that tuner. I only have 22 uh inductors and could use a little more L. Todd KAQ will tell you my tuner is too ugly for pictures.  gfz

What does Todd, KAQ know about tunerasthetics anyway? Come on Todd, 'fess up OM! I personally think my tuna is about as fugly as a tuna gets, but it works well. It's what's inside that counts (That's what I keep telling the yl anyway).

On a more serios note, I use a pair of 40Mh rollers inductors in tandem. I calculated that I could probably get away with something like 26Mh on 160M, but occasionally I like to go to the bottom of the band to work CW. I use approx 5/8 to 3/4 of my L on 1885KC. My antenna is a 260' flat top dipole that has seen better days. I feed it with about 100' of 14 ga 450 ohm ladderline. The large breadslicer type variable cap I use in my tuner is 400pf. I've padded it with about 100pf of C in the beginning, and then realized I really didn't need the additional capacitance, and just wound up using the standard breadslicer without any padder caps.

It seems that lower my antenna hangs, the more L I need to get it to resonate on 160M. Right now it's only up at about 35-40 Ft. or so, but it was up at 75' a few years ago. Countless storms causing it to blow down, and a deteriorating physical condition have prevented me from hanging it up at it's original height. This will however change since my knee operation!

I hope this info helps. If you have any more questions, please ask.

It seems the lower the antenna height, the more dependent it is on L, regardless of the band in question.

Very best Regards,
                        Joe Cro N3IBX    
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Joe Cro N3IBX

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« Reply #19 on: October 25, 2007, 02:31:02 PM »


What does Todd, KAQ know about tunerasthetics anyway? Come on Todd, 'fess up OM!

I know that Frank's tuna looks like something out of a Frankenstein movie. In fact, much of his radio room does! Some of the knobs are bigger than your average steering wheel. Cap'n Nemo would be proud. Wink

I also know that my Johnson Flashbox really does flash, a purty blue color!

Quote
It seems that lower my antenna hangs, the more L I need to get it to resonate

They have pills available now to help that, Joe! Instead of L, add some V or C.  Grin
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« Reply #20 on: October 25, 2007, 04:34:31 PM »

Joe,
That sounds really accurate. At 22 UH I run a bit more than 400 pf but feed line a bit longer. I use 2 300 pf cardwells in parallel with 1/4 inch spacing. TNX om.

Todd,
there is flash box on top of the tuner just in case I blow it up. Maybe I should send Joe a picture of a ugly tuna.
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« Reply #21 on: October 25, 2007, 06:58:49 PM »

Joe,
That sounds really accurate. At 22 UH I run a bit more than 400 pf but feed line a bit longer. I use 2 300 pf cardwells in parallel with 1/4 inch spacing. TNX om.

Todd,
 Maybe I should send Joe a picture of a ugly tuna.


Frank,
        I'd love to see it, and can speak for many others as well. Is there any way you could post a pic or two of it to the BBS?

The uglier they are, the better they work!

Best Regards,
                  Joe N3IBX
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Joe Cro N3IBX

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« Reply #22 on: October 25, 2007, 09:19:43 PM »

OK Joe,
I just sent you 3 pictures for a laugh. You can post them here if you want.
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« Reply #23 on: October 25, 2007, 09:48:26 PM »

Anyone using any sort of lighning arrestors on their system?  Polyphasers or I.C.E. on coax?  Spark plugs or grounding knife switches on ladder line? High impedance choke loops? Static drain chokes or resistors on coax? ARRL equipment insurance in lieu of lighning protection?

I try to bring everything down to coax before it enters the house at a grounded metal input panel with polyphasers.  Have ceramic feed-thru on the panel for an inside tuner for the inverted -L with outside disconnect/grounding switch.
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« Reply #24 on: October 25, 2007, 11:38:46 PM »

A wonderfull topic!!

I like both and have found that ladder line to be the most frequency agile when used with a good link-coupled antenna tuner and a 160 meter center fed dipole. Best part if used with a 160 meter dipole you will find substantial gain lobes at the higher frequencies.

If you use ladder line beware of the feed-line lengths to avoid high voltage points at the tuner. For example, on 160 I would avoid even multiple of a quarter-wave.

Coax provides the simplest approach for most hams. Ease of installation, no sensitivity to placement near metal object; allows for simple chokes to be constructed by wrapping multiple turns at the feedpoint etc. Any length can generally be used without high voltage points at the tuner.

My ugly Tina Tuner:

http://home.comcast.net/~w1ia/

Brent W1IA

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