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K6JRF's Page formerly W6FZC Antenna Repair by JD Electrical Signs Photos by K6JRF |
(New: Jan, 28, 2020 - Update: Feb 18, 2020)
The CD-78 has died . . . High SWR . . .
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JD Electrical Sign Maintenance My 80/20 mtr dipole (CD-78) developed high SWR (> 10:1) in Oct 2019. I called Robert's Sign (owner, Bill Miller) and sadly found that he recently had a stroke and will not be able to provide any services. So I searched the Internet and made a lot of phone calls before I found a bucket truck company. The owner, Juan Diaz of JD Electrical Signs sent his son, Josafat (Joe) to my house and together we did the repair the feed point on the CD78 which has corroded badly over the last 11 years. That's the last time the tower was cranked down for any work. He also replaced all of the missing BirdX Bird Spikes (B-S) that have fallen off over the years. The pulleys were lubricated and cold galvanized. Here's the story in pictures of what was done. |
Two problems: The CD78 developed a high feed SWR (> 10:1) due to corrosion at the feed point. The pictures show the
frontal and bottom views; if you look closely, you can see the rusted connections. The last time any work was
done was over 10 years ago.Also, little by little, most of the B-S have fallen off and need to be replaced. 
As you can see, the LEFT side has lost all of the B-S, where the RIGHT side has all of them. The reason is not
due to the B-S themselves, but the ADHESIVE; the right side used LIQUID NAILS where the left side used the
recommended adhesive. Which one will you use?? Since late November of last year, I haven't been able to find such a qualified person that does this work . . . until I found JD Electrical Signs. The company has been active in San Diego for apx 20 years performing sign maintenance and other sign related jobs. Joe, Juan's son, said that he is interested in this form of business so his company is just the ticket for easy antenna repair and installation. |
The 40 ft bucket extension is integral to his truck and has been in use daily for 20 years. Joe says that his truck
is a workhorse and is going strong. The bucket has full controls on top so it requires only one operator. All motors are hydraulic and is easily controlled from the bucket. The only drawback is that limited bucket extension range of about 40 ft. This requires that there isn't a large setback from the access point to the tower. In my case, it's only about 21 ft, so with the tower cranked down, it just reaches to the top G6-144 antenna. The picture shows Joe maneuvering the bucket to get to the tower. For my installation, there was just enough bucket to reach the top antenna. |
This picture shows Joe replacing the B-S on the G6-144 colinear. The 11 years since the B-S were replaced has taken a toll on the both antennas but especially the colinear so that all of the four (4) radials were bare! The problem is that the recommended "glue" by BirdX is not weather tolerant. The 'best' adhesive to use is Liquid Nails. It holds fast over the years as evidenced by the right side of the CD78 that has ALL of its B-S! |
After the G6-144 was completed, he moved down to the CD-78 and repaired the feed-point area shown in the top pictures. As
is easy, the corrosion (over 11 years!) did its job. The old twisted-cable was replaced with a new one and new SS hardware.
After repair I checked the antenna's SWR . . . and it was the SAME AS BEFORE!!! So the ugly twisted line wasn't the
problem even though it looked to be solidly corroded. The next step was to remove the 50 ohm LMR-400 coax feed line and
see what happened. If you look closely, you'll see that the center dielectric has turned to CARBON and thus has a real impedance! In the shack, it measures 101 ohms. Ain't science wonderful! The factory swaged connector had gotten moisture into it b/c there isn't a 'drip-edge' on the balun that would prevent it from happening. I may add one at later date. Have NEVER had a cable do that in 50 years living in California . . . but there's a first time for everything!! I had a replacement roll of LMR-400 so we cut the old coax near the tower, taped the new end to the pigtail and pulled it up through the coax loops at the end of tower section. Joe sealed the coax connector with silicone and fastened to the out-rigger leg. Never know it happened! 
After the repair, I swept the repaired antenna system for the full 80mtr Ham band (3.5 to 4.0Mhz) using my AA-170
Analyzer. The LEFT chart shows the resonant frequency is 3.817Mhz and SWR = 1.15:1. The RIGHT chart shows
the impedance - |Zr| is 45 ohms at the center frequency. It's just as good as new!
As I observed the ease of the repair, I thought that this is definitely the way to go. I explained to him that a "normal" way of repairing this would be to remove the CD78 via sling on the antenna driven by a rope and pulley get it down. The G6-144 could then be taken down for repair on the ground. To do this takes about 6 - 8 hours including the returning the antennas to the tower. The bucket truck makes it very pleasurable. The bucket is very secure b/c its 4ft deep which comes up to your mid-chest. You feel secure compared to a Stinger Crane bucket that's barely 3ft in depth. I once was up in the Stinger bucket at the end of a 50 ft arm . . . and I think I got seasick when it swung. |
The positive pull-down cable was adjusted and the all pulleys lubricated. The key to proper adjustment is the "idler pulley"
shown at the top of the picture. This keeps a more-or-less constant tension on the cable which goes to the top section.
The pull-down cable was adjusted via the idler pulley and the cable was re-tensioned via the top 3/16" thimbles.
The bearing oil was replaced . . what a terrible job b/c of the placement of the drain plug. . . on the bottom of the
power winch . . making it extremely difficult to get to the plug. Took apx 2 hours to get the plug loosened b/c there's
no way of getting a "normal" tool into the small space. I used Mobil SHC634 synthetic bearing oil. It has exceptional thermal and oxidation resistance which combined with a balanced additive system, provides excellent oil life, deposit control and resistance to thermal and chemical degradation. This formulation also provides low temperature fluidity characteristics exceeding conventional mineral products. |
This a ground shot picture showing Joe from JD Signs adding B-S to the center (left and right) section of the CD-78. The
right picture shows the completed effort so the CD-78 is now "protected" from the birds and so is the pool underneath
the tower!! The tower is extended to apx 90% of its full height. With the light-wind load, I don't have to crank it down
with winds even as high a 50mph!! It was clear blue sky today so the detail of the antenna and tower repair is visible. All antennas have B-S covering the elements so the birds have no place to land! The B-S were put on the antennas using Liquid Nails Extra Heavy Duty formula. So now time will show how well they stay on. An antidote: Before the B-S were added, I regularly saw two small birds fly up and sit about halfway down the length of the CD78. Today, I saw them trying to land. As they flew the length of the CD-78, each tried to land on a B-S w/o success. But they flew to another B-S and continued to try w/o success. Each landing attempt took a fraction of a second accompanied by a LOT of SQUAWKING. Finally, they buzzed the CD78's length and took off!! In summary, the CD-78 antenna's feed point connection (2 wire twisted pair) was replaced and anchored with new SS hardware. Due to the coax connector failure at the balun input, it was replaced w/ new LMR-400 coax. All pulleys were lubricated w/ a synthetic bearing oil and all were cold galvanized to arrest rust. The power winch oil was replaced and the pull-down was adjusted. |
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JD Electrical Signs 559 Blackshaw Lane, San Diego, CA 92173 Cost: $120/hr with no minimum. Time starts at departure from main shop (Logan Heights). Contact Juan at 619-227-0578 Email: jdsigns49@yahoo.com |
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