Introduction |
A friend of mine, that lived down the street, passed away (Ed Byrd, WA6TIQ). Ed's main antenna was a DX Engineering THUNDERBOLTTM installed about 100 feet from his shack. His XYL wanted to get rid of ham stuff so I bought the antenna from her. I has always been curious about the operation of that antenna and I was moving to an area where there wasn't room for all the antennas that I had.
The antenna included a lot of extras like
- Tilt Base
- DXE-RADP-3 Radial Plate
- DXE-SSVC-2P Stainless Steel V-Clamp
- DXE-UN-43 - Multi-Band UNUN
- DXE-UN-BRKT - Mounting Bracket Kit for the DXE-UN-43 UNUN
- DXE-TCB-UNFK - Feed Point Connection Kit
At it's base were 32 - 32' radials connected to the Radial Plate. It had, what appeared to be, four thin nylon or dacron ropes to help support the vertical element. The ropes were tied to screw anchors that were imbedded in a bucket of concrete. The antenna could support itself, but with high winds it is best to provide some extra support.
Because I was working by myself and wanted the antenna to be intact, I took about three hours to deinstall it. When I laid the vertical element on the ground, I managed to twist the bolts that were on the Tilt Base. That wasn't a big deal because I got replacements at Home Depot. Other than that, the rest of the antenna was in good condition.
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Reinstalling the Antenna |
Disclamer: Some of the materials and methods that I used to erect my antenna may go against recomendations in DX Engineering's manual. I am not suggesting these materials and methods. I am simply telling you what I used. I am not asking for anyone to validate my materials and methods. What I used worked for me. You should use your own judgement.
When I took the Thunderbolt down, I lived in Northern Arizona. But when I put it back up, I was in Michigan. In Michigan I had a house on a 3/4 acre lot. That was much less than my Arizona home, but still plenty of room in the yard to put up the antenna. The XYL and I specifically chose a house that was not in a HOA. The XYL would have gone for it but I did not want to deal with that. It's a very nice neighborhood and a nice house. Everyone seems to take good care of their property.
Only once, when I erected a 50 foot crankup tower, did I have someone working with me. For all of my other antennas, I was working alone. Because of that, I first made sure that I had all of the parts necessary and knew the exact order that things needed to be done. It may have taken me a bit longer than needed, but that's OK. I'm retired and there was never a safety issue during installation.
Antenna Base
I located a spot in my yard that was at least 50 feet from anything. If the antenna ever came down on it's own, it wouldn't hit anything or land on anyone elses property. The dirt in this area is very easy to dig in, but the grass is very thick and strong. I had to first cut through the grass, where I wanted to put the antenna mount pipe, before I could make the required hole. Yes, I know that cement is recommended in the mount hole, but I didn't use any. I dug the hole with a small auger which was very slightly smaller than the mounting pipe. Then I simply pounded the pipe in the ground as far as I could. There is about 3 feet of pipe in the ground. Oh, and yes, I did have the propery checked for utilities prior to diging the hole. All my utilities are underground and are in the front of the house, over 200 feet away, and didn't need to be considered any further. You might say that this will loosen up over time, as the antenna moves in the wind. But I will be using guy ropes at 20' which will minimize the movement of the base. In the end, the pipe was very secure and stable.
Radials
Once the mounting pipe was in place, I attached the DXE-RADP-3 Radial Plate and Tilt Base to the mounting pipe. I then started laying in some radials. Installing the radials was time consuming, so I installed them in several sessions. I started with 4 radials. One for each major compass direction. Then I bisected the angles that they formed (90 degrees) and installed another 4 radials. Again, I bisected each angle and laid in another 8 radials. That gave me a total of 16 radials. I have 16 more that will be installed at a later date.
In Michigan, grass grows very well and it's very thick. To keep the radials out of the way of the lawn tractor, I placed them right against the dirt, at the base of the grass. With a thick lawn this is a bit difficult. So I worked from the base using a flat blade screw driver, lawn staples, a rubber mallet, and a tape measure. I would connect the radial wire to the radial plate, stake it with a lawn staple and stretch it out with the tape measure. The tape measure was secured to the lawn at each radial position. That kept me on track. I would then stretch out 2 feet of wire and would use the screw driver to create a path in the grass, so that the wire would lay at the base. I would basically "comb" the grass out of the way so that the wire would lay on the ground. Then I would add a lawn staple and smack it with the mallet. I worked that way to the end of the wire and then went to the next wire.
Installing the radials was done on my hands and knees and was very time consuming. But in the end none of the radials are visable and I can run over them with my lawn tractor. Now you may have guessed that this took a lot of time and lawn staples. Let's see 16 radials 30 feet long comes to about 240 staples. A box of 500 staples can be purchased in their garden center at Home Depot. That should leave me with just enough for the other radials.
Vertical Element
During my rest periods from installing radials, I assembled the vertical element on the ground. I used some fine steel wool to clean the vertical element sections at the point where one element section goes into another. A tape measure (200 foot) was secured to the base of the first vertical element and then each element section was secured at the appropriate distances, as specified in the DX Engineering's manual. All measurements were taken from the base to avoid cumulative errors. When it was all assembled it was exactly 43 feet long. With the base ready, I added the Tilt Base components to the bottom of the vertical antenna element.
Guying
I double checked all of my measurements, several times but didn't find any issues. So I am at the point where the vertical element is laying on the ground ready to go. I didn't want to have to take the vertical element down, so I attached the guy ropes. While this antenna might not need guy ropes, I feel better with them on. For guying I used plastic tent stakes (4) that were about 12 inches long, 4 - 50 foot lengths of 3/8" rope, and a Figure 9 Rope Tightner. I purchased the tent stakes, tightner, and rope in Home Depot. Although, I can't find the tent stakes on-line any more but all three items were in the rope and chain area. Just make sure that they are at least 12" long and sturdy. The wind will try to pull them out of the ground.
I tied all four ropes to the vertical element at the 20' point. There was a connection between two vertical elements, so I secured the rope above the clamp. This keeps the ropes from sliding down the antenna.I then installed the tent stakes evenly spaced around the antenna base, and 20' away, using a rubber mallet. I took care to leave about 1" visible for the rope. Even though I did not need the full 50' of each rope, I did not cut it. I then raised the vertical element. The vertical element is not very heavy but still a little difficult to deal with. You have to be careful that it goes up nice and straight or the Tilt Base may bind up and give you trouble. When I was taking the antenna down, I manged to bend all of the hardware on the Tilt Base, but that was easily replacable in the Home Depot.
At this point, the vertical element is in the air and all of the guy ropes are hanging down. I just took one guy rope at a time, looped them through the tent pegs, and smashed them further into the ground. The Figure 9 made it very easy to secure the ropes to the tent pegs without a single knot. I placed the Figure 9 at about eye level. This was because I had a puppy (Springer Spaniel named Henry) that loved to play with balls of rope hanging down. With the Figure 9 at eye level, I was able to roll up the excess rope and secure it to the guy. However, before the final wrapup, you need to make sure the vertical element is actually vertical. I did this by attaching a level to the vertical element and sequentially tightened the ropes until it was level and the ropes were tight.
The ropes have a bit of stretch to them. This works out very nicely. When the wind blows, trying to knock the whole thing down, the stretch dampens the movement. The top of the vertical element may move a bit, but the guy point buffers that movement, and transfers some of that down the whole element. As the wind abates the vertical element is then gently pulled back to vertical.
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Tuning |
| Band | Freq (MHz) | TX | IND. | ANT. | SWR | Radio/Tuner |
|---|---|---|---|---|---|---|
| 160 | 1.820 | 8.0 | L | 8.0 | 2.6:1 | IC-735/Dentron Jr. |
| 80 | 3.550 | 5.0 | K | 6.0 | 2.6:1 | IC-735/Dentron Jr. |
| 40 | 7.110 | 4.5 | F | 4.5 | 1:1 | IC-735/Dentron Jr. |
| 30 | 10.125 | ? | ? | ? | ?:1 | IC-735/Dentron Jr. |
| 20 | 14.100 | 8.0 | B | 5.0 | 1:1 | IC-735/Dentron Jr. |
| 17 | 18.100 | 5.0 | B | 6.0 | 1:1 | IC-735/Dentron Jr. |
| 15 | 21.100 | 4.5 | C | 10.0 | 1.1:1 | IC-735/Dentron Jr. |
| 12 | 24.850 | 4.5 | A | 10 | 1.5:1 | IC-735/Dentron Jr. |
| 10 | 28.100 | 4.0 | A | 5.0 | 1.2:1 | IC-735/Dentron Jr. |
I have two wideband antenna tuners to work with. A MFJ-941D and a Dentron Jr.. I started with the MFJ-941D, but I had a lot of trouble obtaining a good match on some of the bands. And, while I was testing, the Inductor Switch started to freeze up. So I opened the tuner up, and applied some WD-40 to the switch. First I applied the WD-40 very sparingly to the shaft bushing. I did this before on the MFJ-941D's Antenna Selector switch, and it worked fine. However, this time it didn't work. So I looked at the interior of the box and noticed that there was some steel balls on a track that ran around the switch. I packed the area around the switch with rags, so that no oil would get on anything but the ball track. One short spray from the WD-40 can, cleared the frozen switch.
But I was still having trouble getting a good match, so I switched over to the Dentron Jr.. That tuner performed much better. I was able to get a good match (< 1.5:1) on 40 through 10 Meters. However, I couldn't get the SWR on 80 and 160 Meters below 2.6:1. While that is actually usable, I was hoping for something better.
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Doing better on 80/160 Meters |
The DXE Thunderbolt does work well, but doesn't tune well on 80 and 160 Meters. However, Phil Salas - AD5X, has several publications on getting a better match with 43' vertical antennas. AD5X simply uses several inductors that are installed at the feed point. MFJ also has the MFJ-2904 Range Extender that provides a nice simple way to get better matching on 80 and 160 Meters. Any of these approaches can be automated with some remote relays.
I will forgo adding anything for 80/160 Meters for the time being. I don't go to either band very often and the existing antenna match is sufficient. Maybe in the future I will rig something up with some inductors and jumpers.
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