Wednesday, September 4, 2019

E. U. N.

Some time ago, I read a blog article on how to prioritize requirements. The author called it N-U-N analysis. The letters stood for Needed, Useful, Nice. I thought this was a brilliant idea, but the acronym was awkward, because there were two "N"s. I decided to traded the first for a better synonym: Essential. Essential, Useful, Nice. E. U. N. This is a powerful organizing principle.

I recently was dealing with a ham radio project list that had gotten too long. I had a number of great ideas which I had added to the project list, so it crossed several pages of my station log. This made actually finding something I could work on difficult -- especially when dealing with projects that could actually add value.

Mulling this over, I decided I needed to apply the same principle to my project list. But what was Essential, and what was merely Nice? and how about the Useful projects in between?

I decided to break it down this way:
  • Essential - fixing what is broken
  • Useful - allowing new capabilities
  • Nice - anything that might be a nice addition
I organized my long list, and low and behold it was very helpful. I only had a few projects in the Essential section, but one of them I had basically forgotten (fixing a broken switch contact on the Ameritron AL-80A).

Several of the projects were in the Useful category, and I'll be getting those done sooner. Everything in the Nice category can wait a bit.

I can't say that this exercised has helped me get anything done sooner, but now I know my efforts will be focused on the most valuable projects.

Sunday, August 25, 2019

Rebuilding the HF4B

It's been a long time since I picked up the Butternut HF4B project from a friend. I decided it would be a good fit at the Fulton County QTH. It's small enough to be supported by a mast, and will turn with a tiny rotator. I took all of the pieces to Fulton County, disassembled and cleaned everything, and took stock of what I needed.

The basic components seem to be OK. One of the 1/2" tubes is damaged with a gouge near the end, nearly ran over by a lawnmower no doubt, but will be serviceable. One of the 1 1/8" element support tubes has a crack. I've looked for a replacement locally without luck. I think for the moment I'll use a clamp to hold it together.

Two of the four doorknob capacitors have cracked. I managed to find five 75 pF caps at a hamfest a couple of years ago. I bought five in order to have a spare. These things are fragile.

All of the stainless hardware is serviceable despite being out in the weather for over 25 years. The U-bolts, however, are another story.

I don't know what genius thought it was a good idea to sell an antenna with zinc-plated U-bolts, lock washers and nuts. After 25 years of weather, they are rusted junk. Some of the legs broke off when trying to undo the nuts. Those that didn't are so rusty as to be unusable for any purpose.

I ordered replacement U-bolts from McMaster-Carr, who had exact replacements for a reasonable price. Except these are stainless steel.

With replacement hardware in hand, I started to re-assemble the antenna. The wires of the bowtie elements needed replacement. This antenna has eight of these, but only four survived to make it home with me. Of these, only one is intact. I used it to make measurements and make eight identical replacements.

I hit the a snag assembling the first element. The clamps that hold the vertical tubes aren't tight enough to keep them from rotating on the support tubes. Butternut replaced these sheet metal clamps with U-bolts in a later release, which would work better. This requires sleeving about four inches of the vertical tubes.

I guess that's what I'll have to do.

Friday, August 2, 2019

Demise of the 80/40m Dipole

Sad to say, I recently lost my 80/40m trap dipole. Which is too bad, because it was a good antenna. I used this antenna from four different locations in Georgia: Gwinnett, Floyd, Walton and Fulton counties. I made thousands of contacts on this antenna. It had been the first antenna I put up at Floyd and Walton counties, and the only antenna at Fulton county.

It was last up at the parsonage in Fulton county. Apparently a group of teens was doing some volunteer work near the parsonage. They saw the rope tied off to the parsonage fence and thought it was something other than it was, so they untied it.

After this, half the antenna fell down to the ground and was left there. When the landscapers came by to mow the grass, they ran over it....

So, about 80 feet of rope, insulator and one of the traps was completely destroyed. The other half of the dipole is still intact, up in the trees. But most of one element is gone -- clearly the landscapers threw it away.

Plan is to design an 80/40/20m trap dipole, using traps made with coils and capacitors, since they have much higher Q than the coax cable traps. I'll also place the traps on frequencies well off the operating frequency.

Tuesday, March 26, 2019

Uh Oh. Not Good.

Well, if it isn't one thing, it's another. After celebrating getting the A3S/A743 rotating again, I've found a problem. The SWR shifts I mentioned? On a dark night, I went outside and looked up at the antenna while WSJT-X was transmitting on FT8 trying to contact someone. I tried this on 40 and 20m.

I observed one of the 20m traps on the driven element light up with arcing using 100 watts. It was visible in the drain holes and end caps of the trap.

At the very least, I'll need to take the driven element down and rebuild it.

Update: I've tried this experiment on 15m, and I see no SWR shifts even using 500 watts. I think the problem may be confined to the 20m trap(s).

Monday, March 25, 2019

Rotating Again!

Well, it didn't take months after all. As I wrote last month, my A3S/A743 had been stationary since December. But with the beautiful spring weather here in Georgia, I managed to get to the top of the tower and finish the installation.

It's now rotating freely, as expected. It's really good to be able to use the beam as intended, and not have it fixed roughly east.

I do wonder if the A3S/A743 needs repair, however. I'm still seeing occasional SWR shifts at 100 watts on 40 and 20m. I'll need a gin pole to take the antenna down to refurbish.

Thursday, February 28, 2019

Back on the Tower Again

During my December vacation, I started a rather ambitious project on the tower. Since its installation, my A3S/A743 has been about eight inches from the very top of the mast. My intent was to put the beam at the very top of the mast, in order to give more room to stack an A50-3 under it.

It had been a while since I climbed on the tower, and any work at the very top is always nerve-wracking. As I've written before, sometimes you get up there and decide you've had enough.

Anyway, back to the December project. I conscripted my daughter Lauren to be my ground crew. I ascended the tower, removed the rotator and hung it from a couple of nylon loops off the side of the tower. Then I lowered the mast into the tower, until the A3S/A743 bracket was right at the top of the tower. The mast and antenna are somewhat heavy, weighing about 50 lbs. I relied on a pulley at the top and bottom of the tower and a haul rope to get support from my ground crew.

The tricky part of this operation was going to be moving the antenna higher on the mast. I had two options. First, I could loosen the bracket U-bolts, lift the antenna higher, then retighten. This would only take me about five hands, and I was only born with two. Second, I could loosen the bracket U-bolts, then lower the mast into the tower. While this seems easier, I had visions of the mast going too low and the antenna falling off the tower. Plus, I was afraid that we'd drop the mast and it would fall some 40-some feet into the base of the tower. And then the antenna would fall off the tower.

Plus, my daughter was having a lot of trouble getting sufficient leverage on my pull rope, which was 1/4". After being at the top of the tower a little over and hour, I decided to continue the project later.

Little did I know that it would take two months before I could get back up there!

In the intervening time, I had purchased 120 feet of 9/16" braided black poly rope. Our first order of business was to replace the existing 1/4" rope with this much more substantial lanyard. Once again with my trusty ground crew, we set out to complete the project.

With the bigger haul rope installed, I surveyed the top of the mast. I had thought that perhaps the antenna had slid down the mast in the 18 years it has been up. But a close examination of the mast showed no evidence of that. It had always been at that level.

Standing there 40-some odd feet in the air, 20 feet above the edge of my roof, I wondered if loosening the antenna would get me into a whole new world of problems. I decided at that moment I wasn't going to mount the A50-3 under the larger beam. What we needed to do was hoist the mast back and up and put the rotator back in place.

This proved to be a problem. Despite all her hauling away on the rope, Lauren was unable to raise the mast any significant distance. It was only with me grabbing the mast with two hands and pushing we were able to move it at all. I ended up locking down the mast with a couple of bolts in the tower and climbing down to solve the problem.

I had a ratcheting come-along, but hauling it up and using it on the tower was problematic. I ended up tying the come-along to a support pole, then hooking it into the haul rope via a tied loop. This would allow Lauren to use the come-along to provide lift, and I could manage things at the top of the tower.

After climbing back up, things moved a little more quickly. The come-along provided plenty of tension, but I found that I had to move the mast with my hands to get it to budge -- there's just too much friction and too much stretch in the poly rope. In a few minutes, we had the mast nearly back up into position. I had to re-position the pulley to get the last few inches to make room for the rotator.

With the mast locked down again, I hauled the rotator back into position. Thereupon I discovered two problems. First, one of the four nuts on the U-bolt that clamps the rotator to the mast was missing. In the two months on the tower, it apparently shook loose and fell off. Second, the rotator connection at the base of the rotator were loose -- one of the forked lugs had fallen off the wire and would need to be replaced.

Not having the necessary hardware at the top of the tower, I finished as much of the assembly as I could and came down the tower knowing that this project would be finished on another day. Hopefully, it won't take a couple of months to get back up there.



Friday, February 15, 2019

Mark V.5 Shunt Feed Matching Network (75 & 80m)

Additional capacitor for 80m at lower
right, relay is black box just above.
Three years ago, I improved my shunt-feed matching network for 75m by upgrading to a T200A-2 core and a way more beefy variable capacitor. It tuned my shunt-fed tower quite nicely to a 1:1 match around 3800 kHz. And it could easily handle a little bit of power.

However, when using the antenna on the low end of 80m, the match isn't quite so nice, reaching nearly 3:1 at the bottom of the band. I needed to be able to re-adjust the network when operating there.

It occurred to me that additional capacitance would do the trick, along with a way to switch it in. I found good capacitor of about 25 pF and suitable plate spacing. Switching it was more of a problem.

I wanted to use a large, 12 volt, open-frame relay. Unfortunately, I didn't have anything in my junk box, and couldn't find anything I liked at a hamfest. Eventually, I settled on using a PC board style relay. I figured it had enough of a contact gap to avoid arcing.

Mounting it, however, was problematic. I ended up just having it floating in the box, suspended by the wiring connections.

Side of box showing the control voltage wiring, the 75m
tuning control (upper right) and the 80m tuning.
After re-wiring, the network tuned up nicely on 75m, but there wasn't quite enough capacitance to bring the match down in the CW portion of the band. I ended up putting to 33 pF 6 kV capacitors in series across the 25 pF variable, essentially adding 16.5 pF to the circuit.

That did the trick, and I got a 1.1:1 match around 3570 kHz. VSWR at the bottom edge of the band was under 2:1.

The existing four-wire bell cable control lines were re-purposed to drive two relay circuits. The existing frame relay selects between the 75/80m and the 160m matching networks. The additional relay is energized to bring the additional capacitance online for 80m.

This works so well, I'm surprised I didn't try it earlier. With a better match at the antenna, losses in the feed line and antenna tuner are reduced.