Tuesday, August 27, 2013

KT34a to KT34M2 Upgrade and Rebuild

Last year I purchased an old KLM KT34a antenna at NEARfest. I discovered that M2, after purchasing KLM, developed a kit to rebuild and upgrade the antenna to a higher standard of construction. This made sense as I was sure the antenna would need a complete rebuild. I threw it on the roof, drove it home, threw it against the house, and left it for a year. BIG MISTAKE. Every element was full of bug crap. Mud daubers and earwigs. Yuck. Worse, their poop corrodes aluminum. Here is the system I'm following to clean the elements.

On the day before you plan to the work, remove the 1" tube from each element.

If it's siezed to the 3/4" element at it's swaged joint, don't force it, instead disconnect the 3/4 element from it's insulator and leave attached to 1" tube. Clean out the bug crap. Use the hose, get the big chunks, run a brush if you can. We'll need to hammer the 3/4" element through the 1" element, but the 1" element is double tubed and any debris inside it may make it difficult to remove the 3/4" element. Clean this well.

Spray seized joint thoroughly inside and out with Parts Blaster. Set the element down at an angle with the tip down. This allows the BLaster to pond up in the swage. Leave overnight. Do not skip this step. You may continue to disassemble the rest of the antenna at this point.

The next day, using a block of wood at each end and the BFH, attempt to pound the smaller seized element into the larger element. Lubricate it with WD-40 first. It may take some effort, and the elements are relatively strong against this type of force, but still take care not to bend or snap them. Once it's flush use another aluminum tube of the same size to drive the smaller element clear through the swage. Again, lubricate the tube first.

Don't be like me and brake off a 3/4" element inside a swaged 1" element. It was stuck and I was flexing it to work in the blaster, gently I thought, and snap. DX Engineering sells a 3' length of 3/8" tube for the whopping price of $1.50. Of course they have a $20 minimum order, plus shipping. But since M2 quoted me $48 for the part I decided to pad out my DX Engineering order.

Completely disassemble the rest of the elements. Sort out the hardware you need to reuse from everything else. I think you just need the insulators and clamps.  Mine all came apart easily. If any are seized use a technique similar to above. Tape the element pieces into bundles, one per element.

After experimenting, I found a good quick way to clean out all of the elements. I used long thin fiberglass rods. Wrap some tape 3-4" from end. Split end down to tape. Slip in a piece of scothbrite.  You'll need to cut it to various sizes to fit in each element. It's helpful if you start with the largest diameter element, that way you can trim the scotchbrite down to fit the next smaller element. I put the end of the rod in my drill. I dip the scotchbrite into a bucket of soapy water, insert into the element, and set the drill to hyper drive, and run it in and out. Rinse out, inspect tube inside, and repeat if necessary. Wet scotchbrite inbetween elements. The scotchbrite shouldn't be too tight, it should be very easy to insert, so you can go quickly. It shouldn't spin the whole bundle around. You may have to hold onto the smaller elements to keep them from sliding out of the bundle.

Inspect elements internally for corrosion. If any structural elements are deeply pitted you might consider the wisdom of putting it up 50' in the air where part of it could become a vertical missile.

I broke one of the long 3/8" tubes. I flexed it a bit and it snapped. It had been badly corroded inside by mud dauber cement. It only needs to hold up it's own weight so I am planning to repair it with a sleeve.

I need a way to keep these guys out. I'm looking at using a bit of foam or even window screen and a cap or some tape.

I finally brass brush out the inside diameter of the tubes which make electrical connections. If you are not going to reassemble for some time you may wait until then to perform this step.

I haven't quite settled on the perfect way to clean the outside of the pipes, but I've made some progress.

I use a jig to apply scotchbrite while I spin the tube with the drill.

The jig has gone through a few iterations. So far the most effective approach has been to use a spring clamp to pinch a dogbone sponge wrapped around the scotchbrite and element. Spin to it presses on table. Keep wet with soapy water, this can make some heat. Using some sort of wide strap around the sponge might help.

I'm also experimenting with a wooden jig. Haven't quiet perfected it yet.

Spinning the elements is easy. The smallest fit right in the drill chuck, although you have to be careful not to squeeze them to hard and compress them, or spin them in the chuck.

For the next size up I use an inner wrench on the swaged stub section and clamp it to it's smaller element.

The remaining tube sizes take inner wrenches. The 1" wrench is a very tight fit it might take some wiggling.

I ordered a set of four General Tool inner pipe wrenches from Amazon. Many suppliers seem to carry the exact same set, including McMaster, and Sears. You also need to have the right size socket to drive them and a bit to socket adapter for the drill. Tape the wrench and the socket together so it doesn't fall out.

Now you should have a nice set of shiny tubes with a better than new brushed finish. Reassembly is the reverse of disassembly. Hah! I don't actually have the kit yet, this is as far as I've gotten.

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