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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 20633 times)
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W2XR
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« Reply #25 on: October 26, 2007, 12:38:14 AM »

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.

I use a big-ass military surplus knife switch here at W2XR where the 600 ohm open-wire feeder immediately enters the basement. This switch is connected thru a heavy gauge copper grounding strap that goes directly to a ground rod located just outside of the house. When the station is not in use, the switch is of course thrown to the "grounded" position. Unrelated to this thread, I also open the 120 and 220 VAC circuit breakers that supply prime power to the shack, when it is not in use.

I used a piece of 1/4-inch thk Plexiglas to replace one of the basement windows where the 600 ohm feeder enters the basement; this Plexiglas was drilled to accomodate a pair of porcelain bowl-type feed-thrus, and this makes for a very neat and clean entry point. I also fitted weatherstripping around the perimeter of the Plexiglas window to provide for a tight weatherproof seal. The homebrew balanced-L tuning network that makes the transition from 50 ohm coax to the balanced 600 ohm open-wire transmission line is located about 5 feet from the entry point into the basement. This provides for a minor nuisance, as the shack is about 20 feet from the tuning network; you have to get up, and walk across the basement and tune it anytime you QSY. But it does beat those installations where the locally-tuned ATU is located out-of-doors and an appreciable distance from the operating position.

I don't believe that Polyphaser, et al, make a lightning arrester designed for use with open-wire transmission line. I have seen the website of one enterprising ham who did use a pair of conventional automotive spark plugs as lightning arrestors for use with his open-wire feeders.

Just my 2 cents worth.

To quote the title of a very old QST (or maybe it was CQ Magazine) article; Open Wire Feeders Forever!!

73,

Bruce
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W1UJR
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« Reply #26 on: October 26, 2007, 07:22:31 AM »

Anyone using any sort of lightning 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 lightning protection?

Good question, a real issue if you've got balanced line feeding right into the housing. Some hams just disconnect this from the outside when a storm threatens, and throw the feedline away from the house. Simple and it works, if you are home to do it. I had a nasty experience with a lighting strike last year, so did some research. My take on the Polyphaser or spark plug/arc systems is that  it only makes a difference on static discharge for storms, or nearby local strikes. A direct hit is almost sure to get you, no matter what system you have in place. The tremendous amount of energy that is required to jump 5,000 feet to the ground is going to ignore the 1/8" gap on the spark plug, and likely vaporize any of the lighter Polyphaser gear.

With that said, its a very good idea to protect against static buildup during a storm. A few years back I was at my office hamshack during a nearby storm, and kept hearing a snapping noise. I looked up, and saw an arc between the two metal antenna feed-through bolts, snap, snap a few moment before I heard the thunder! Shocked me, the metal rods were at least 4-6" apart, imagine what that would do with a ricebox connected to the antenna. Even a tube rig would likely sustain damage to its RF coils.

In my experience, for nearby strikes, yes, do what you can to mitigate them, as for direct hits, your pretty much done.
See the photos below of a strike sustained at W1UJR last July.
Spilt a 100 foot tall pine tree from top to bottom, and blew out a number of electrical items in the station and house.
http://www.w1ujr.net/lighting_strike.htm



That's just my 2 cents Sonny.  Grin



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WD8BIL
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« Reply #27 on: October 26, 2007, 08:10:30 AM »

Quote
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.

Hmmmm..... I'm cornfuze Tina.

A dipole, let's use ur 160 story see'ins that's where I'm headed, at optimum hieight feeds at about 72 ohms. Low voltage high current point. At lower heights it's lower. For instance, EZNEC says my future dipole at 80 feet hi dipolio will be 30.5+8j Z. Pretty Low.

 Now, wouldn't a 1/2 wave feeder (even multiple of 1/4 wave,180 degrees) show the same -Z at the tuner ?? (-Z indicates the phase shift.) And wouldn't this appear at EVERY half wavelenth along the line whether even our odd ?? (I know there are other effects of the even 1/2 wave but we'll ignore them for the sake of this discussion).

And if so, a half wave feeder would be what you want to keep the voltage off the tuna.
Am I thinking wrong here ? Remember, I'm just a buddly  Cheesy
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W1QWT
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« Reply #28 on: October 26, 2007, 08:35:56 AM »

Here is my grounding knife switch on my balance feedline.
I have replaced the connecting wire shown in this picture with a larger gauge.



The balanced tuner, 450 ohm feedline, and 75 meter dipole allow me to operate on
160 - 6 meters. The 3/8 inch pipe goes down 5 feet to a 6 foot diameter copper ring of pipe in the
ground. It is like a spoke assembly on a wheel the center of which is a 6 foot ground rod.

On my coax fed antennas I use polyphasers for lightning protection.

Regards
Q, W1QWT
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Steve - WB3HUZ
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« Reply #29 on: October 26, 2007, 09:51:59 AM »

The nice thing about using a link tuner is you can ground the center of the antenna side coil for static drainage. This won't provide lightning protection on the order of physically disconnecting the feeders, but it's better than having the antenna floating.
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Todd, KA1KAQ
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« Reply #30 on: October 26, 2007, 02:08:14 PM »


I use a big-ass military surplus knife switch here at W2XR where the 600 ohm open-wire feeder immediately enters the basement.

IIRC TrueBruce, it's one of the ART-13 switches? They come in single, double, or triple pole configurations. Those are excellent for that purpose, along with the old copper electrical types you saw at my place on the 'Wall of Knives' and in the garage. Not only do they work well, allowing you to switch the ant to ground when not in use, they add to the Frankenstein look of the station.  If you gap it ever so slightly from ground as a storm approaches, you can see little zorches occur. Cheesy

Quote
I don't believe that Polyphaser, et al, make a lightning arrester designed for use with open-wire transmission line. I have seen the website of one enterprising ham who did use a pair of conventional automotive spark plugs as lightning arrestors for use with his open-wire feeders.

To quote the title of a very old QST (or maybe it was CQ Magazine) article; Open Wire Feeders Forever!!

Glad to see I'm not completely out of touch for using the 'feeders' term. Still recall several SKs telling me to use  'Balanced Feeders' or Open wire feeders with one ant for all HF bands. Never did it, but I still remember.

Along the lines of the spark plug approach is the old 'horn' approach, using pieces of formed aluminum tubing bent just so, and adjusted to a small gap from the feed thru bowls to ground. Collins has a diagram in some of their transmitter manuals complete with measurements, I've also seen them at BC stations and elsewhere. 

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W2XR
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« Reply #31 on: October 26, 2007, 06:40:06 PM »


I use a big-ass military surplus knife switch here at W2XR where the 600 ohm open-wire feeder immediately enters the basement.

IIRC TrueBruce, it's one of the ART-13 switches? They come in single, double, or triple pole configurations. Those are excellent for that purpose, along with the old copper electrical types you saw at my place on the 'Wall of Knives' and in the garage. Not only do they work well, allowing you to switch the ant to ground when not in use, they add to the Frankenstein look of the station.  If you gap it ever so slightly from ground as a storm approaches, you can see little zorches occur. Cheesy

Quote

Hi Todd,

Great memory! Yup, it's a double-pole configuration. Actually, I obtained all three (the single, double, and triple-pole variants) of these knife switches from the estate of a local SK who passed on a number of years ago. They were all in the dumpster awaiting their potentially sad fate, when master dumpster diver W2XR rescued them. The double-pole knife switch you saw here at the station is nomenclatured "AS-13/U". And yes, these switches definately do add a 1930s Frankensteinian motif or aura to any shack.

One time, I deliberately opened the switch up just a hair while I was transmitting unmodulated carrier at the full legal limit. Talk about pulling an RF arc! Not recommended practice on a frequent basis.

BTW, had a great day with Joe/PJP today; he just left the QTH a little while ago. We are preparing to get our CY-979As refinished.

Talk with you soon below 3800 Khz, & hope that all is well at your end.

Best 73,

Bruce
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WA1GFZ
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« Reply #32 on: October 26, 2007, 07:57:59 PM »

When I go away I lay a couple pipes over the feed line pulling it to the ground.
Bruce I have pretty much the same set up with the basement window but just drilled a couple holes for the feeders to pass through. A spark plug will flash over at a low voltage. Remember the old handbook articles with a spark gap made from copper cut to a point. I have an old telegraph spark gap. that I modified.
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Vortex Joe - N3IBX
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« Reply #33 on: October 27, 2007, 09:34:24 AM »

Enclosed are a few pics of Frank, WA1GFZ's "fugly but beautiful" tuner. I think everyone would agree that it's what's inside that counts!

Mod-U-Later,
                 Joe Cro N3IBX




http://s50.photobucket.com/albums/f338/n3ibx/?action=view&current=gfztuna.jpg

http://s50.photobucket.com/albums/f338/n3ibx/?action-view&current=gfztuna2.jpg


http://s50.photobucket.com/albums/f338/n3ibx/?action=view&current=gfztuna3.jpg
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Joe Cro N3IBX

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« Reply #34 on: October 27, 2007, 10:56:48 AM »

Quote
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.

Hmmmm..... I'm cornfuze Tina.

A dipole, let's use ur 160 story see'ins that's where I'm headed, at optimum hieight feeds at about 72 ohms. Low voltage high current point. At lower heights it's lower. For instance, EZNEC says my future dipole at 80 feet hi dipolio will be 30.5+8j Z. Pretty Low.

 Now, wouldn't a 1/2 wave feeder (even multiple of 1/4 wave,180 degrees) show the same -Z at the tuner ?? (-Z indicates the phase shift.) And wouldn't this appear at EVERY half wavelenth along the line whether even our odd ?? (I know there are other effects of the even 1/2 wave but we'll ignore them for the sake of this discussion).

And if so, a half wave feeder would be what you want to keep the voltage off the tuna.
Am I thinking wrong here ? Remember, I'm just a buddly  Cheesy
Dislexia gets me again BUddly...ArrgH!
ass-backwards...sorry

Brent
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« Reply #35 on: October 27, 2007, 11:48:34 AM »

Single line feed, " the other white feed, not often seen in better amateur circles."

My arguably 'best' or should I say most used antenna is a somewhat random length windom 138 ft. (total) fed 30 ft. off center with an approximately 50 ft. length of single line feeder from a rotary coil/cap "L" network.  The dimensions were defined by tree distances and in no way represent much of a decent plan.

 So I guess, not counting the 6' or so coax feeding the "L" net tuner up on the basement windowsill, that it's not a balanced feed or coax fed antenna.  It's a single line radiator right out of the shack.

You don't want to look too closely at the MMANA (JE3HTT's) plots for this antenna too closely. - All over the place, but that's what makes it interesting.  Seems to work fine most of the time.

A/C MMANA, on 160 & 80 I'm loading up the vertical feeder and using the whole top as a capacity hat and on higher freqs, the horizontal element seems to be the radiator.  Ground? Outside the window to a couple of ground rods. Also my E service is buried for a distance of of 200' or so.  I think that's my 160 ground : )

Yeah, there're also 40 and 20 meter dipoles here but rarely used.  Come to think of it, much of my stuff is rarely used.  Gotta get on the air more.
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ka2zni
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« Reply #36 on: October 28, 2007, 04:54:36 PM »

Gonna try some stuff from w7fg , with a Palstar Balanced tuner, The Coax Fed 75 Meter antenna at 90' seems to be beating out the 450 Ohm ladderline antenna ... It's a pain to swap antennas out, BUT , I wanted to know the difference from this particular QTH...

I was surprised to see the coax stuff beat out the other... I am going to try one of w7fg's set-ups probably and see what the difference is.

The Coax fed antenna is done with LMR-400 , DX-Engineering Current Balun, The 450 Ohm Ladderline antenna is done with the obvious and a Palstar Balanced Line Tuner with L/Network ...

Both Antenna's cut same length and hung in the same configuration, I did not expect too see what I have for results, Now we will see what will happen with true Open wire feedline.

The 450 Ohm stuff SUCKS in the rain too by the way...


'73's, More results later on!
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« Reply #37 on: October 28, 2007, 06:01:29 PM »

Quote
The 450 Ohm stuff SUCKS in the rain too by the way...

I have been using the 450 ohm feedline for a number of years now and I don't
notice any problem when it rains other than the tuning points may be slightly
different. Currents are still balanced and signal reports are fine.

Regards
Q, W1QWT
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ka2zni
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« Reply #38 on: October 28, 2007, 06:14:20 PM »

I'll have to get your version of 450 ohm, this stuff I am using is terrible in the rain. Probably some cheap junk I picked up I am sure, Knowing my luck.
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W1QWT
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« Reply #39 on: October 28, 2007, 06:35:50 PM »

I think I bought it from wireman.
Maybe in some installations it is more susceptible to moisture?
I remember that when I was in the Navy when we were at sea in a bad storm
some of the antennas would tune up differently than when they were dry and
other antennas didn't seem to be affected. We had both wire antennas and vertical pole types. Unless the atmospherics were bad we could still contact land however.

Reminds me of a funny story. There was one antenna that suddenly became very hard to load into. I took a stroll back to the fantail to see if that vertical was still there.
Sometimes in a bad storm they would snap.
Seems somebody decided to run a wire clothes line from it to the life rail and used metal wire. Flapping from the clothes line were sailors skivies!
I have heard people say you can load up a bedspring but underwear?

This was a submarine tender so the fantail could not be seen from the bridge
so the officers never saw it.







Regards
Q,
W1QWT

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The Slab Bacon
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« Reply #40 on: October 29, 2007, 08:35:51 AM »

The 450 Ohm stuff SUCKS in the rain too by the way...

You must have some really crappy stuff. I have been using the 14Ga crappy brown stuff for years with no problems in the rain.

It may take a slight retweak of the tuna, but thats about it. I do have to retune slightly when its coverd with ice, but thats about it.

If you are experiencing a lesser performance with your balenced feedline, you may want to take a closer look at your tuna. Also make sure you are using the heavier stuff and not the wimpy 16 or 18Ga stuff.
the thinner guage stuff can exhibit some I/R losses when ran at a low impedance for a long run.

                                              The Slab Bacon
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k7yoo
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« Reply #41 on: October 29, 2007, 09:58:31 AM »

Try not to use the floppy solid conductor ladder line for long term installations. This usually has 18 ga copperweld that fractures inside the insulation after a short period of flapping in the breeze. The rectification that usually occurs at the breaks will make you think your receivers have all developed image problems and will make you go nuts trying to track it down. It also tunes strangely and can create spurious emissions galore. I used the stranded 14 ga stuff for years with no problems but currently use 10 ga flexweave homebrew line.
Skip
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ka2zni
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« Reply #42 on: October 29, 2007, 10:29:47 AM »

This stuff was stranded 14Ga... And the tuner is a Palstar BT1500A ... I really don't think it's the tuner. It only did it in the rain storms we had this week.

I run on a small bandwidth, I am not concerned about bouncing all around the bands, Just putting a good signal out on 2 of them as efficiently as I can.

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The Slab Bacon
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« Reply #43 on: October 29, 2007, 11:16:41 AM »

Kevin,
        I have never heard of or seen a "Palstar" tuna. If it was created for the ssb / ricebox groups, it may well not handle the duty cycle of high powered AM. My tuna is homebrew, it will handle anything that you can throw at it.

For the hell of it, make a long "old buzzard" transmission at your highest power level. After you unkey, lay your hand on the top of it and see if it is getting warm. If it is, you know where your power is going. If it is getting hot, it is dissapating some of your power. (that which is heating the tuna is not going to the antenner). I have seen many tunas rated for "legal limit" power melt down with well less than "legal limit" AM power levels. Here is a good opportunity for a little home brewing!!

                                                   The Slab Bacon
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The Slab Bacon
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« Reply #44 on: October 29, 2007, 11:24:26 AM »

Also, what I forgot to mention is that you will really see the advantages of the ladda line vs coass is when you try to use the antenner on a band / frequency OTHER than what it was cut for.

Losses should be pretty close when the antenna is a 50 ohm match. But as the antenna's impedance goes up (longer antenna @ higher frequency) is really where you will start to see the ladder line out perform the coass.

                                                         The Slab Bacon
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N3DRB The Derb
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« Reply #45 on: October 29, 2007, 11:50:24 AM »

I gotz the w7fart gas stuff comin soon.
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w3jn
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« Reply #46 on: October 29, 2007, 01:53:21 PM »

An I got a bigassed ol Gonset leenyar in my garage waitin for the right time  Grin
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Steve - WB3HUZ
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« Reply #47 on: October 29, 2007, 02:07:06 PM »

Some good info on wet ladder line losses below.

http://www.vk1od.net/G5RV/
http://www.ocarc.ca/coax.htm
http://users.triconet.org/wesandlinda/ladder_line.pdf



And the spark plug based arc gap design some one asked about previously is at

http://www.athensarc.org/ladder.asp
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w5omr
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« Reply #48 on: October 30, 2007, 01:09:37 PM »

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

Probably not as prevalent a change on say 40m and up, where 1 1/4 wave is only 30~35 feet (depending on soil conditions).

But, lower in frequency, it makes sense that you'd probably need more critical L tuning, as you'll have more C between the antenna and earth.  The more C you have, the less L you need.  This might be why the NVIS antennas seem to work... inductive reactance (XL) is nearly 0 and you'll need more capacitance to tune say, a 160m antenna, that's only 30' off of the ground.

To answer the poll, I noticed the most -marked- dramatic difference when I changed my Inverted Vee feed-line from 50Ω coax to 450Ω ladder line.  Then, I closed up the bottom of the inverted vee with another 120' of wire (since I was now using an impedance matching device anyway) and created a full-wave delta loop.

I'm constantly told that the mere 100w I run (according to the meters and gauges) sounds like other stations that are running 300w or better, with better-than-average audio.

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« Reply #49 on: October 30, 2007, 02:18:42 PM »

I'm constantly told that the mere 100w I run (according to the meters and gauges) sounds like other stations that are running 300w or better, with better-than-average audio.

Well, of course they say that, because you're big and scary Geoff. They don't want you dropping a 610 on them.   Grin

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