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Author Topic: Hustler 6BTV Vertical with Bouncing SWR - Part 3  (Read 1371 times)
KB3MDT
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Posts: 205




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« on: March 21, 2013, 09:22:27 PM »

Hi,
   After several weekends I was still having problems with my Hustler 6BTV Vertical and erratic SWR.  I just finished rebuilding the four traps this afternoon.  Two of the traps had rust underneath the steel rivets that fastened the trap coils to the aluminum poles.  I ground off the heads of the rivets, cleaned everything up, and used brass screws as replacements for the rivets.  I used Penetrox on the electrical connections as I did the reassembly.   I used my bench grinder to remove the ends of the screws extending beyond the nuts so that they were flush.   Otherwise, the bottom of the screws would have been too close to the aluminum trap covers for comfort.   For good measure, I ground off a little of the screw heads also to play it safe.  Note, I only run 100 watt max, not legal limit.   I used a center punch to make a small depression at the "thread boundary" of the screw and nut to help lock them in place.  (at least that's the theory).

  I put everything back together and ran some tests.  Still the occasional erratic SWR, plus I couldn't get the SWR below 2.5 on 15M.   Grumble, Grumble, Growl.   Its only 30 degrees outside with occasional snow flurries.   I removed the antenna base and took it completely apart.  I removed all the scale on the plastic insulators, and checked for any arc traces in the plastic.  Everything looked good.  I put everything back together and did more testing.  Still the occasional erratic SWR.

  I decided to "reinspect" (i.e. remove tape) the barrel connector between the main coax line and the "new" antenna pigtail I installed 2 weeks ago.   It seems raising and lowering the antenna about 100 times on the tilt mount caused the connection to come loose.  Plus, the "new" $1.99 PL-259 barrel connection already had some oxide on the center pin.  I went to my parts box and found that some of the "Brand New" barrel connectors also had traces of oxide.   I found a good barrel connector, tightened up the connection, and taped it all back up.   
 
  More testing, and still problems.  I temporarily replaced the entire RG-213/U coax run (about 100 feet) with some used RG 8/U coax.  15M SWR dropped from 3+ to under 1.75.   Okay, something must be up with my feedline, even though its less than 1 year old and worked perfectly with a Dummy Load instead of the antenna, one of my first tests. 

   I decided to take the RG-213/U coax directly into my shack, bypassing the New Alpha Delta "Spark Arrestor"  (I replaced the old one last week).  This also eliminated a 10 foot section of RG 8/U that ran through the wall from the Spark Arrestor to my Tuner.   Last week I replaced every cable in my shack except this piece of RG 8/U because its a pain to replace.   I thought it was a piece of Belden RG 8/U, but it turns out it was Radio Shack RG 8/U.   Ahhh!     

  Anyway, I connect everything back up minus the extra piece of Radio Shack RG 8/U and the Alpha Delta "Spark Arrestor".  **** SUCCESS *****.   SWR on all bands is good, showing a lower SWR in the middle of each band than at the edges (how I tuned up the antenna). I also have lots of ground radials.    I reran my tests and the SWR holds steady.  No more SWR randomly jumping from under 2 up to 8 and beyond.  I'll add the Spark Arrestor back in later this weekend after I make up a new cable using a piece of RG-213/U coax.

  Some Lessons learned:

1) A tilt base on a vertical antenna is invaluable!
2) The Coax Feedline can be bad even if a test with a dummy load instead of the antenna looks good.  I wish I had a Domain Reflection Meter (or whatever they are called) to test coax.
3) Cheap coax connectors aren't worth it.   Go for the good stuff!
4) Suspect every cable in the path between your rig and your antenna.  Don't assume its good just because the connectors look clean or the cable is new.  Don't use Radio Shack Coax (I've heard this before).
5) Document every change as you repeat your tests.  (I used a spreadsheet).
6) Corrosion is your enemy.   Seal every outside connection carefully.
7) Test your antenna with a short coax cable and Antenna analyzer if possible. I did all my testing with my 100 foot run of coax and the SWR meter on my rig.  The long coax run distorts any antenna SWR readings.  It also meant many trips from the basement to the back yard and back every time I made a change.   **** Most important, I would have quickly realized the problem was not the antenna if I used a short piece of coax from the beginning for all antenna testing ****.
Cool You might have more than one problem, making trouble shooting more difficult.

On the bright side:
1) I got lots of exercise with all the trips up and down the basement steps.
2) All this fun only cost me $50 for a tube of Penetrox and replacement hardware (mostly new Hose Clamps).

I hope you enjoyed my trials and tribulations.  The *^&$#$ antenna better work tomorrow morning!

73
Ken
KB3MDT


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WX2S
Member

Posts: 736




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« Reply #1 on: March 22, 2013, 03:08:25 AM »

Congrats on finding a tough one!

I believe you're thinking of a TDR:

http://www.amazon.com/Fluke-Networks-MS2-100-MicroScanner2-Verifier/dp/B000QJ3G42/ref=sr_1_6?ie=UTF8&qid=1363946406&sr=8-6&keywords=time+domain+reflectometer

73, wx2s.
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73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
WA3SKN
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Posts: 5499




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« Reply #2 on: March 22, 2013, 05:30:57 AM »

Glad you found the problem!
But you should start with a known good dummy load at the transmitter and work toward the antenna to locate problems like this.  Everyone should have a dummy load available for testing.
73s.

-Mike.
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KB3MDT
Member

Posts: 205




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« Reply #3 on: March 22, 2013, 06:27:17 PM »

Hi,
    I did use a new Dummy Load (MFJ 260C 300 watt) to try to find the problem.  First at my Transceiver, and then again with the cable feed at the base of the antenna.  It showed no problem. I did not try the dummy load just outside of the house where I have a connection to an Alpha Delta Spark Arrestor.   I should have tried here also.

    I only ran a 30 watt test signal to the dummy load for about a minute and probably only at one or two frequencies.  In retrospect, I should have run the test several times at multiple frequencies and higher power levels.   The dummy load was sitting outside in 30F weather and didn't even get warm.    My problem was intermittent, and somewhat frequency dependent.   I never gave the dummy load a fair chance to find the problem as I could have sworn it was the antenna.

   On the bright side, my wife saw my frustration while I was working the problem a couple of weekends.   She gave me the OK  to order a new YouKits / TenTech FG-01 antenna analyzer.  You can use it to check cables as well as antennas.   :-)


73
Ken
KB3MDT
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W8JX
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Posts: 6144




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« Reply #4 on: March 22, 2013, 07:21:42 PM »

My nickle is on the spark/lighting arrester.
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KD8IIC
Member

Posts: 160




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« Reply #5 on: March 23, 2013, 01:49:12 AM »

My worst antenna ever was the 5BTV. Junk, but learning costs money. Home brewed a replacement vert for 40. Now have MA8040v, works FB...73
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W8JX
Member

Posts: 6144




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« Reply #6 on: March 23, 2013, 07:44:15 AM »

My worst antenna ever was the 5BTV. Junk, but learning costs money. Home brewed a replacement vert for 40. Now have MA8040v, works FB...73

Was my best, nearly 20 years of reliable service and still in service.
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W6EM
Member

Posts: 833




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« Reply #7 on: March 23, 2013, 05:32:19 PM »

.....  I ground off the heads of the rivets, cleaned everything up, and used brass screws as replacements for the rivets.  I used Penetrox on the electrical connections as I did the reassembly.   ......
73
Ken
KB3MDT



Ken:
You should have replaced the rusty rivets with stainless steel screw hardware, not brass.  Brass in contact with aluminum will result in electrolytic corrosion over time.  You will probably be OK for a while, but the aluminum will begin corroding when the penetrox dries up a bit and allows moisture to penetrate under the brass screws.

73,
Lee
W6EM
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AA4HA
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Posts: 1497




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« Reply #8 on: March 23, 2013, 07:35:37 PM »

A couple of other ways to test out that feed-line;

Open it at both ends and ohm it out. It should test as infinity. Note that any sort of water in the feed-line may show as a drifting resistance as electrolysis from the DC battery changes the moisture content. (DC converts the water to hydrogen and oxygen gas but also forms a battery action and encourages rapid corrosion)

A better way to check feed-line for water is to use a current limited, medium voltage AC supply and a micro-ammeter. With the feed-line open and you putting in a few hundred volts (current limited) there should be absolutely no current flow from shield to center pin. Do not get yourself shocked, current limiting at those voltages may be with a 30-100K resistor.... also, you could just check the voltage across current limiting resistor. If there is no current flow there will be no voltage drop across the resistor (ohms law).

Testing with RF is another useful tool. We know that a dummy load and wattmeter across your transmitter will show you the full power of the transmitter. Now if you took the dummy load and wattmeter out to the base of the antenna you could unhook your antenna and plug in the wattmeter/ dummy load right at the antenna base. Then, working with a partner, they could key up the transmitter and you should see the transmitter power less any losses due to the feed-line. You would want to look up the losses for your particular type of coax, at a specific length and on a specific frequency. This is also another way for you to test all of your in-shack jumpers and that surge arrestor device. Losses are usually expressed in dB/100' so either remember the "rule of threes" in dealing with dB or use an on-line calculator to convert that into wattage drop.
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W8JX
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Posts: 6144




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« Reply #9 on: March 23, 2013, 08:55:25 PM »

You should have replaced the rusty rivets with stainless steel screw hardware, not brass.  Brass in contact with aluminum will result in electrolytic corrosion over time.  You will probably be OK for a while, but the aluminum will begin corroding when the penetrox dries up a bit and allows moisture to penetrate under the brass screws.

Not exactly. If the mass of both parts were they same aluminum would tend to be sacrificed but given the large mass of aluminum vs brass screw there really should not be any increased decay in aluminum due to the "galvanic sinking" of its mass. The least reactive fastener with aluminum is actually galvanized or "clad"and is the preferred fastener bolting steel or stainless to aluminum. Also remember that some aluminum alloys are more stable than others too. Pure aluminum is not that strong. It is the alloying that gives it its strength. 
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