Last June, 2006 was our first attempt at a Field Day. A few of my ham buddies grabbed some radios, threw some wires up in trees and tried to see if we could actually pull off a Field Day and generate RF. We did it so we decided to do a little bit better for 2007.
Our Field Day site is an athletic field with goal posts at each end. In 2006, we stretched an long wire between the goal posts (approximately 300 ft.) and used that as a SSB antenna. We didn't get the results we wanted so we decided to try to put up a more aggressive antenna....a full size beam.
Since we hadn't been very serious about Field Day the first time, we didn't want to invest a lot of money in the beam/tower project. So...I started looking around for a used beam. There are plenty of them around but I couldn't find one in the St. Louis area. Then one day, I was checking our local Craigslist and found a listing for a Mosley TA-33 tribander. The seller was Larry Steimel KDØDG. Larry showed us a beam that had been disassembled and stored on the ground for about 15 years.
Here is a photo of it as we first saw it:
He assured us that the beam had been working just fine when he disassembled it 15 years ago. Larry listened to our pitiful story about Field Day and agreed to sell us the TA-33 for $50.00 (thanks Larry!).
Luckily, one of the prinicpal organizers of our Field Day event is Bill Plumpe, WØETR. Bill has a full machine shop and we put it to good use refurbishing the TA-33. First thing we did was gently clamp the traps in a vice and begin disassembling them by pulling the end caps off:
Next...we removed the screws that attach the coil in the trap to the trap cover.
Then we slid each trap out of it's cover. Some didn't look too bad:
Others were caked with mud:
Still others had insect nets inside:
We first started to work on cleaning the trap covers since they are electrically part of the trap. We put each trap cover in the lathe and spun it around while removing the corrosion with steel wool. Here's a typical trap cover before cleaning.
Here is the trap cover spinning in the lathe being cleaned with steel wool:
We also used a giant forceps to hold onto the steel wool while cleaning the inside of the trap:
Here's what a cover looks like after the corrosion has been removed with steel wool:
Look at the pile of shiny covers!
We did the same thing with each element of the beam. Here are the elements after they've been steel wooled clean in the lathe:
Next we gently cleaned each trap with soap and water:
Now that the traps were clean, it was time to evaluate them. One of the known failure points of the TA-33 is that the forms on which the traps are wound can crack over time and cause the antenna to not tune. Most Mosley traps over time will crack. Sometimes, the cracks cause problems, sometimes they do not. We don't know of a reliable way to evaluate traps with the naked eye to determine if the cracks will make trouble. Virtually every trap we had was cracked throughout the former material.
Over time, Mosley Electronics recognized that the cracks in the traps could cause problems. Initially the trap forms were made of a light-colored "white-ish" material. Mosley switched to a darker "black-ish" material that is supposed to resist cracking. Conventional wisdom is that the darker material is the prefered one as it's composition resists cracking. When we disassembled our antenna traps, we discovered that we had 10 white traps, 1 black trap, and 1 purple trap. We had never heard of a purple trap. Here they are all lined up and ready for re-work. The "purple" trap is third from left and the "black" trap is the right-most trap:
We decided to do a leakage test with a megger to see if a high voltage would cause leakage across the former material. To do this, we had to electrically disconnect the aluminum trap wire from the aluminum trap tube. Toward the middle of each trap, the aluminum wire is riveted through a hole in the former material onto the aluminum tube. We needed to drill out each rivet. Replacing the rivet wasn't a bad idea anyway since those can be failure point in this antenna. We gently clamped each trap in the vise, used a hose clamp to hold the aluminum wire in place and removed the rivet by drilling it out:
We attached one terminal of the megger to the trap's aluminum wire, the other terminal to the aluminum tube, and measured the voltage across it. we were hoping it would be zero. For 11 of the 12 traps, the voltage was near zero as seen on the meter:
For the 12th trap, the "black-ish" one, we did register a voltage on the meter:
This was the opposite of what we expected. The "black-ish" coil formers are supposed to have the better properties and only the black one showed leakage. We were initially concerned because there was a crack in this former in the section where the coil was wound. Could this be a bum trap? Bill, WØETR, suspected that the darker former material might just leak a little more than the lighter color and that the trap was still ok. To test his theory, we carefully examined the former for a section with no cracks. We wound some scrap wire across this uncracked length and re-tested. Sure enough, there was leakage. This suggested that despite the leakage, the trap was ok...or at least wasn't inoperative due to the cracks in the former material.
We reinstalled the rivet we had removed with a rivet gun. Even though the traps seemed to be good, we wanted to address the issue of the cracks while we had everything apart. Bill, WØETR, had equipment to vacuum impregnate the formers with epoxy. Bill made a little metal tray to hold the trap and poured epoxy into the tray. Bill then put the tray in a vacuum chamber, pulled a vacuum and then released it. The epoxy was drawn into the cracks in each trap until they were completely filled. We now had crack-free traps. We don't have any photos from this step as it was a messy process. I left the camera in the car that day!
With the TA-33's aluminum cleaned up and the traps vacuum impregnated with epoxy, it was time for our first full-blown test. We wanted to make sure the driven element (radiator) on the beam was working before going any further. If the driven element had a fatal flaw in it, then we'd have to solve that problem before turning to the reflector and director. To test the driven element, we assembled it, connected coax, and lifted it up at least 1/4 wave above ground with a truck mounted crane. Here's the driven element on the crane and ready to be lifted!
We raised the crane boom until we had the radiator up about 17 feet:
We connected the coax to an MFJ-259 antenna analyzer and held our breath...it worked! It's not easy to see in the photo below but we have an SWR of 1.4:1 at 14.253 mHz. Woo-hoo!
We assembled the rest of the TA-33 and began to turn our attention to the tower. Sam Effinger, K9SD, generously lent us 4 sections of Rohn 25G, a hinged base-plate, and Ham IV rotor with control box. Thank you Sam! Bill Plumpe, WØETR, had some strong steel automotive ramps and he bolted the hinged base plate to one of them. The plan was to drive Bill's truck onto the ramp and use the truck weight to hold the base in place. Once the truck was positioned, we'd use the bed-mounted crane to pull the assembled Rohn 25G up into position. Here's a photo of the hinged base plate tipped up and bolted to the steel ramp. You can see the bottom of the tower near the base ready to be installed:
The truck is now positioned on the ramp to which the hinged base plate is bolted:
For our test raising of the tower, Jim Cline, KCØDTD, helped attach the cable from the truck-crane to the tower:
Though we later used a heavier duty sling, for our test-lift, we used a ratchet strap as a sling to attach the cable to the tower:
We're ready for the first "lift" of the tower and here she is coming up off the ground! Note how the rotor is very close to the top of the tower. We moved it up there so we'd have the maximum height above ground for the beam. We made a change after we saw how much stress the vertical mast was under after we attached the beam. You'll see it in the later photos:
Here's Jim, KCØDTD, attaching the mast to the rotor.
Since Rohn 25G is not a self-supporting tower, we had to add guy ropes. Here is Bill, WØETR, preparing the guy ropes prior to lifting the tower vertical.
We've assembled two of the three elements of the TA-33 on the ground and boom is now connected to the mast. Once we lift the tower a little higher, we can add the third element to the boom:
Here's a photo from a little farther away showing the partially-assembled beam on the mast and the tower supported by the truck-mounted crane.:
The truck-mounted crane has pulled the tower vertical. As you can see we didn't get all the elements of the TA-33 lined up in the same plane on the boom. This was just a test raising and we'll get it right on Field Day:
Here's a better image of the TA-33 up on the tower:
Now that we had all that aluminum and steel in the air, it was ready for a "smoke" test. We fired up the Honda generator, powered up the Yaesu FT-100 on the truck bed, and tried to make a contact. We started with 20m CW and worked W1TBT in Westborough, MA on the first call (and the back of the beam). We then QSY'd down to 15 meters and worked K8JT/4 in West Virginia. K8JT asked us to QSY down to 10 meters but the band was too dead to hear anything. Then, we went back up to 20M phone and worked a station in Virginia (again off back of beam) and then another one in Washington state. Not bad for just a few minutes of testing and check out.
Field Day was just a week away and we still had a little work to do. We moved the rotor to the section of the tower just below the top section. This significantly reduced the load on the lifting crane. Bill, WØETR, made a set of heavy-duty ground anchors for our guy ropes. The light-weight ones we used for our test were too unstable. We also noticed when attaching the reflector and director to the boom that we were missing the mounting blocks for those elements. Bill cranked those out in his machine shop and we were ready to go!
We first set out the drive-on base plate with the hinged-base bolted to it and lying flat. The other tower sections and the disassembled beam are visible on the trailer in the background:
Jim Cline, KCØDTD, and Bill, WØETR, slid the bottom section of the tower onto the hinged base which is tipped up 90 degrees:
Bill, WØETR, bolts the tower section to the hinged base:
In this photo, you can see the entire tower (all 4 sections) assembled on the ground and attached to the hinged-base plate:
Bill, WØETR, drives the truck with the bed-mounted crane onto the drive-on plate. The big white crane boom is visible above the truck cab:
Rich Robertson, NØPQU, steadies the lifting cable attached to the sling:
Rich Robertson, NØPQU, Jim Cline, KCØDTD, and Bill Plumpe, WØETR, assembled the TA-33:
Fred Simowitz, KØFS, Rich Robertson, NØPQU, and Ken Pfitzer, WØHRO, hoist the beam up to the mast.
In this photo, you can see the guy ropes attached to the tower and the crane boom with cable attached to the sling. The tower is partially raised to allow the beam to be mounted on the mast. From left to right, Jim Cline, KCØDTD, Fred Simowitz, KØFS, Derek Cohn, WBØTUA, Ken Pfitzer, WØHRO, Rich Robertson, NØPQU, Bill Plumpe, WØETR, and Mike Ragouzis, NØOBI.
We attached a choke balun from "The Wireman" to keep the RF off the shield of the coax. This was an excellent suggestion from Bill Thomas, K1XT. I read up on using choke baluns after Bill's suggestion and ordered one right away from "The Wireman". Feeding a balance antenna like a dipole or beam with an unbalanced line really works best if you have a choke balun.
Ken Pfitzer, WØHRO, tightens down the thrust bearing bolts to the mast.
Now that the beam is attached to the tower, it's ready to be pulled up. The winch on the crane was activated and up she goes!
The whole assembly looks much bigger when you include people in the photo:
Here's the base of the tower, attached to the hinged-base plate coming into position:
Here's some of the crew taking a well-deserved break after assembling the tower and beam. Mike Ragouzis, NØOBI, Rich Robertson, NØPQU, Ken Pfitzer, WØHRO
Here's the sideband station that is using the TA-33. Joe Winkelmann, ABØQD and Ken Pfitzer, WØHRO:
Here's another shot of the sideband station knocking 'em dead with the TA-33. Ken Pfitzer, WØHRO, Bill Plumpe, WØETR, Paul Kulick KCØFCC, and Joe Winkelmann, ABØQD:
Here's Mike Marx, WBØSND, making contacts on 40 CW. You'll notice the Johnson Matchbox in this photo....we used the beam for the phone station. The CW station is using a 135' dipole fed with balanced line and coupled with this Johnson Matchbox.
Here's a view of the 135' dipole from DX-Engineering. It's fed with 300 ohm balanced line:
We had a wonderful time at Field Day and hope to do it again in 2008!