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Author Topic: Did I mess up my antenna? - cut the ladder line..  (Read 40049 times)
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AB2EZ
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"Season's Greetings" looks okay to me...


« Reply #50 on: April 21, 2014, 04:22:43 PM »

I just noticed that, in one of his above posts, Opcom provided a reference to a product description / specification sheet from the manufacturer of this antenna:

Tekrad_Mark_V_antenna_system_small.pdf
 

Reading the information there, I deduced the following:

1. The four legs of the fan are, in fact, each made of ladder line

2. The write up says: "The feedpoint impedance of the antenna is a nominal 450 ohms balanced, and is fed by a 450ohm balanced transmission line"

This makes me suspect (there is not enough information the manufacturer's write-up to be sure) that the intended antenna consists of two folded dipoles, connected together at the feed point location in some manner (probably in series at the feed point location; but maybe not).

This would imply that the integrity of the connections (far ends of each leg shorted, center ends of all four legs properly connected in a folded dipole configuration of some sort) is critical, and suggests (to me) that the center connection arrangement in this particular antenna (as installed, maybe after shaking the antenna to clear a short*) is not correct.

*You wrote:

"Months ago, the wind blew the center insulator around and made a short but some jiggling on the rope, which has become slack, fixed that. I can see up there with binoculars."


Stu
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Stewart ("Stu") Personick. Pictured: (from The New Yorker) "Season's Greetings" looks OK to me. Let's run it by the legal department
flintstone mop
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« Reply #51 on: April 21, 2014, 08:19:26 PM »

Stu
I will have to say that you are a very thorough investigator/troubleshooter.
OPCOM didn't say that the fan dipole was a ladder line of sorts.

I think an old problem came back to his antenna in the last quote.
hmmmm
Fred
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Fred KC4MOP
AB2EZ
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« Reply #52 on: April 21, 2014, 10:50:27 PM »

Fred

Thank you!

Stu
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Opcom
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« Reply #53 on: April 22, 2014, 04:36:05 AM »

Stu, that is very good analysis. It is totally made of ladder line, all the same kind.

IIRC the far ends of each leg are not shorted.
I don't think it is a folded dipole but I will look with the binoculars just to check.
The connections on the center section are very rugged, all wrapped several times around and soldered extremely well. They should not be easily damaged, but there was that previous incident.

I never used 80M much, and the issue of heating up the balun only showed up during long winded turns at the RT. Now I want to use it more.

It is like this old post, save the width being 1" not an erroneous 2".
http://amfone.net/Amforum/index.php?topic=26545.msg255887#msg255887
Worked fine with a tuner+balun  then but it was 100W SSB only, so not a good comparison as there is not measurement info from then.

This is the post where the antenna was discovered twisted around and shorted:
http://amfone.net/Amforum/index.php?topic=35465.msg273168#msg273168

and in about my second post I noted:
"R was 100 Ohms at 7160KC was what it was when working."
That is how it had been, before. Now on 7160, it's not tuned at all and R= about 0. No feedlines or anything was changed in between.

===

Stu's remarks helped me recall that there was resonance before at about 7160, and the R coming out the coaxial connector was 100 Ohms (I forget which balun was in use, maybe the 1:1). Anyway a decent R at 7160, which is not being had now. So there is an antenna problem. I have to go try to see it. I hope that during the time when it was shorted and I was pushing a lot of power into it, there was not some kind of arcing between wires maybe burning one of them. I also remember there are alligator clips just at the inside wall of the shack and they ought be checked. Tomorrow with the binoculars will tell. BTW holding them still enough while zoomed into that thing 55FT away is not simple. Wish me luck in finding the trouble!

---
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flintstone mop
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« Reply #54 on: April 22, 2014, 06:48:27 AM »

I have grown suspicious of any solder joints that live outside. If your center feed for that antenna was with common everyday solder; then I would guess that might be where your trouble is lurking.
I think Silver Solder is a better approach for a longer lasting connection.
It might look good, and it might be worthwhile to lower that center point down and re-do it.
I hope you designed a maintenance feature into your antenna so, you can inspect and repair when trouble comes around.
Fred
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Fred KC4MOP
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« Reply #55 on: April 22, 2014, 07:53:16 AM »

If the entire thing was made from ladder line and was supposed to play on multiple bands it may have multiple doublet lengths hidden within the insulation.

One or more ends may have welded itself to something at QRO.
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aa5wg
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« Reply #56 on: April 23, 2014, 12:29:07 AM »

Opcom,

Some of the guys have mentioned the good value of feeding a dipole with coax.  This works very well as a single band tool (excluding the 40 meter dipole that can work on 15 meters).

Multi-band operations should use open wire feeders with the correct antenna coupler design.  The link antenna coupler is the tuner of choice for open wire feeders.

Link provides mechanical and electrical balance, tuning convenience in the shack, eliminates components that can break down under low and high power applications plus it affords one to add shunt reactance (an extra capacitor or inductor between the left and right sides of the ladder line) in the shack to add or subtract electrical antenna system length if needed.

Link also allows one to current feed and voltage feed their antenna system.

Link is simple to operate and once all the bands have been tuned and the tuner settings written down it is fairly fast to tune.

Coax = single band and works very well.
Open wire feeders = multi-band = link antenna coupler.

73,
Chuck
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Opcom
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« Reply #57 on: April 23, 2014, 02:06:56 AM »

I have to get the tower guy over. He might take a look for a trade of something.

It can't be lowered without undoing all 4 ends because the tower guys are in the way.

There is also 30FT up, a stand off and I can't tell if a wire is touching the metal post or not.
Whatever happened in the storm the pulley rope is in a wrong position and 6-9" of one side of the fan looks barely crooked or odd way up top.

I did try the MFJ without a 1:1 balun. Got good "R" in various places and the same resonances, so the 'zero' is probably an artifact of the balun. note the 1:1 balun has never been overheated, and I have tested the MFJ with a resistor, and the balun also with the same resistor.

I better forget about this until I can get someone to go up, and Jacob over to help us.

Regardless of what is a right or wrong way, coax, matchers, etc, the thing worked before, and someone has to go up and check it first.
Otherwise changing any of those other things makes no sense.
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« Reply #58 on: April 23, 2014, 10:47:40 AM »

OK OPCOM
we were thinking that you were able to do some hands-on troubleshooting to your system and get you back on the air
Fred
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« Reply #59 on: April 24, 2014, 01:02:13 AM »

All of that I could do, was done and I appreciate all of the advice.

It's a tower climb now. The man that has done the tower work before, and might do it for a swap, is recuperating from a broken rib. Oddly after the miles and miles of towers all over the world he has climbed without being harmed, it was a freak accident that he fell out of bed and cracked a rib. I pray for his recovery, and not just because I need this fixed. The guy is some 75 years old and in better health than I. He deserves to get well soon!
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« Reply #60 on: April 24, 2014, 09:30:45 AM »

That gives you time to fabricate a new doublet and feedline to replace the existing unknown Smiley
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Pete, WA2CWA
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« Reply #61 on: April 24, 2014, 02:48:14 PM »

Put the antenna on a pulley system so that you can raise and lower it to inspect, repair, etc.
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« Reply #62 on: April 24, 2014, 07:24:54 PM »

I went through my old antenna book, and couldn't think of any reasons that you'd be heating up a balun with an antenna of this sort. It's a "plain vanilla" 80 meter dipole from what we know, so there should not be enough reactance to heat a balun like that.

After wracking my brain for a couple of hours, I took the liberty of asking Mike Gruber, W1MG, to run some numbers on the computer at the ARRL lab. Mike was very helpful, and provided these results:

Frequency3.885 MHz
---------------     ------------------------------
Zl70 Ohms
Feedline length89 feet
Feedline Z450 ohms
Zc (Complex)122.4 -j332
Zc (Polar)354 ohms @ -69.8 degrees

... which show, as we've all figured already, that there's nothing remarkable about the system in theory. Mike agreed with everyone on the board: something's wrong, and it's time to look further. He suggested lengthening the feedline (the 1/2 wavelength point is at about 115 feet for 450-ohm ladder line on 3.885), and I agree that would be a good first step.

I also suggest some other tests:

  • Check the grounds on the tuner and transmitter: you might have a circulation path.
  • Borrow or make a new 1:1 balun, and rerun the curves you published before.
  • Examine the antenna as much as possible from the ground, and look for signs of arcing, charring, or other damage.

HTH.,

73,

Bill, W1AC
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Opcom
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« Reply #63 on: December 20, 2015, 10:14:51 AM »

conclusion http://amfone.net/Amforum/index.php/topic,40863
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aa5wg
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« Reply #64 on: December 25, 2015, 05:00:01 PM »

Here is 2 cents worth.

The least lost and greatest in tuning flexibily is achieved with home brew ladder line feeding a balanced antenna.  The antenna tuner should be the link antenna coupler.  As one changes bands so does the current distribution on the line and antenna.  Thus, the balanced mechanical and electrical properties of the link antenna tuner can accomodate these changes.  A heating "balun" know today does not exist and thus no heat loss.

The most efficient multi-band system is the Link Antenna Tuned system.

Good Luck!
73,
Chuck
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flintstone mop
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« Reply #65 on: December 25, 2015, 06:55:05 PM »

Put the antenna on a pulley system so that you can raise and lower it to inspect, repair, etc.

That's what i have ALWAYS done for a dipole. They are always prone to trouble and mother nature
Fred
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Fred KC4MOP
aa5wg
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« Reply #66 on: January 04, 2016, 11:46:14 PM »

Here is 2 cents worth:

K1JJ suggestion of using independent antennas will work.

AB2EZ, W3GL, K1KW and others have excellent suggestions.

The bottom line is baluns have fixed resistive requirements to work at optimum.  They cannot adjust for reactance which is present in a multiband antenna (some reactance too with mono-band antenna but not bad). 

Thus, to cure the challenge the link antenna tuner is the design for such a multi-band antenna.  Use series tune for low impedance at the tuner and parallel tune when impedance is high at the tuner.

The is no balun to fry.  Many adjust a link coupler to preset dial settings to obtain high efficieny and multi-band use.

Good luck!
73
Chuck

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