Automatic Antenna Selector Project

Auto Antenna Selector under test.

Some projects are years in the making. October 2020, I ordered the KK1L 2x6 Antenna Switch board. I assembled it and by December I rigged up a manual antenna selection switch. Two years later, I mounted the KK1L to an aluminum panel to create a Single Point Ground (SPG). While all that work was beneficial from a bonding and grounding standpoint, antennas were selected manually. If I changed bands and forgot to change the antenna selection, trouble could ensue.

The purpose in buying the KK1L 2x6 Antenna Switch was fully automatic antenna selection. I needed a controller that could communicate with the Elecraft K3 and select the right antenna. 

A PIC microcontroller seemed suitable. I'd had success using one of these chips to build a K9AY Controller. For that project I had used a PIC16F1503. After that, I picked up the PIC16F18426 and PIC16F18446 chips -- these offered more features than the '1503, including a serial port and way more program memory. The Microchip tools were free, and I had a PICkit3 programmer.

I sketched out three designs.

Design A - 1 radio, 1 set of relays

The most basic design - it does little more than replace the manual switch. A single DE-15 jack brings the BAND0-3 information from the K3 into the PIC. Three outputs drive a 74LS145 BCD decoder to select one of the six relays through a 2N3906 driver transistor. Two other outputs allow selection of the 160 or 80/75m shunt matching networks.

Total I/O required nine pins, which any of the three chips could provide.

Design B - 1 radio, 2 sets of relays

A limitation with Design A is that a K3 with the KAT3 has two antenna jacks, but the selector only chooses one antenna. Design B reads BAND0-3 from one radio, and selects the best antenna on port A of the switch, which is connected to ANT1, and the second best antenna on port B, which is connected to ANT2. The operator can then use the ANT button on the K3 to switch between the two antennas. 

This design retained the four inputs for the BAND0-3 information, plus six outputs feeding two separate 74LS145 BCD decoders, and two additional outputs for the 160 or 80/75m shunt matching network. 

That's exactly 12 pins -- still possible using any three of the chips.

Design C - 2 radios, 2 sets of relays

I liked Design B, but along the way I purchased a second Elecraft K3. If I were trying to use both radios, what would I need to switch the antennas?

Two DE-15 jacks facilitate the BAND0-3 data from each radio, requiring eight inputs. The selector could then choose the best antenna for both Radio A and Radio B, unless that choice caused a conflict, in which case Radio B would get the second-best choice.  Outputs were the same as in Design B. 

This required the 20-pin '18446, because the 14-pin controllers don't have enough I/O available. 

It occurred to me I might want to switch the antenna selection priority sometimes, so Radio B gets the best antenna in a conflict and Radio A gets second best. That required an input pin for a pushbutton and an output to light an LED. This used all the 18 pins available on the '18446. 

Design Choice - B/C - 1 or 2 radios, 2 sets of relays

First look with front panel assembled

The end design combines Design B and C features. Two DE-15 jacks are used, and the PIC software decides if a K3 is connected or not based on the pattern of BAND0-3. Unconnected pins are pulled up, so a value of all ones indicates no connection. If only one radio is connected, the software acts like Design B, if both radios are connected, it acts like Design C. 

The front panel has LEDs for the six relays on port A and B, so you can visually see which antenna is selected for each radio. An LED each for the 160 and 80/75m shunt selection, and a pushbutton and LED for the mode selection rounds out the front panel. A power switch and a switch to choose between the 80 and 75m shunt network round things out.

Power requirements are simple. A port relays take 88 mA, and B port relays require 44 mA. Selecting one relay for both ports is less than 140 mA. The 160m shunt relay requires 120 mA and 80m relay requires less. The power requirements of the PIC, 74LS145 and LEDs are negligible by comparison -- 300 mA covers everything. 

Construction

A look at the guts of the box. The relay
drive transistors dominate the board

I searched for a smart-looking cabinet for this project fitting the dimensions of the station. I found a reasonably priced enclosure on Amazon.com. I took lot of care drilling the front panel so that everything lined up correctly. I figured I might be staring at it for years. In retrospect, the rear panel doesn't look so pretty.

With the cabinet in hand, how to construct the hardware? I considered developing a PC board, but I was eager to build. I ended up using a bit of perfboard and some 3M Scotchflex prototyping sockets. The Scotchflex system is now obsolete, mainly because everything is surface mount, but I had most of this in the junk box. I had to engineer a 20-pin 0.3 inch socket -- which I accomplished with two 14-pin sockets back to back.

The downside to this approach is all the wiring required for the relay and LED driver transistors -- there are fourteen 2N3906s, three 2N3904s and a bunch of related resistors. A PC board would have taken more design work ahead of time, but the construction would have gone quickly and taken less space.

I worked on this project off and on in six different locations - Gwinnett county, Fulton county, Warren county, two locations in Gordon county and finally from Floyd county. For a while, I carried the whole project with me in a small cardboard box wherever I was.

Software

Like the K9AY controller, everything is interrupt-driven. The '18466 CPU is configured with a 500 kHz clock speed, and a timer interrupt occurring every 5 ms. 

During the interrupt, we sample the A and B ports from the radios, plus the mode button. All of these values go through debounce logic - the value must hold for 10 interrupts (50 ms) before taking action.

If either the A or B values change, or the mode selection changes, then the antenna selection logic is followed. If either port is all ones, it indicates a radio isn't connected, so the Design B rules are used to select the antenna. If neither port is all ones, we assume two radios are connected, and Design C rules are used to make the selection. 

Debugging

Unlike the K9AY controller, I had a bit of trouble getting the software working. Part of the struggle was knowing if a problem was a wiring problem or a software issue.

At first, nothing seemed to work. In the end, I wrote really simple firmware that just blinks the mode LED based on the timer. Nothing. Setting up the chip on a solderless protoboard, still nothing. After some experiments, I got the timer interrupt straightened out and had a blinking LED on the protoboard. 

Then came the wiring issues on mode LED. One issue was the transistor drivers for the LED didn't have proper pull-ups. Eventually, I settled on a one second startup routine that would blink the mode LED briefly once, then twice. After that, the chip would be looking at the input ports and selecting antennas.

In the next phase, I wrote an additional startup routine that selected the antenna for ports A and B. Every second or so, it selected a different relay, and hence light the LED. I coded it to go in a pattern so I could verify that each relay driver and LED worked correctly. Of course, it didn't work.

Several wiring problems became apparent. First, the 74LS145 chips weren't getting any +5 volt power, so they weren't doing anything. They had been wired, but one of the wires broke. Once fixed, the LEDs lit. Then it was apparent they were going in the wrong order. 

The wiring between the PIC16F18466 and the 74LS145 chips had two problems. First, the pins for the A port and B port had been reversed. Second, outputs from the 74LS145 were reversed. Putting out a value of 001 into the 74LS145 selected antenna 0, and a value of 110 selected antenna 5. Rather than doing a massive amount of re-wiring, it was easier to change the software and re-draw that part of the schematic. 

Then we finally come to the business end -- hooking up the K3 BAND0-3 inputs. That's when I found my last wiring error. Turns out, I had swapped the pins between rig A and rig B. Another problem solved with a software change.

It Works! Now What?

Even with the basic software running, I felt the need for change. I've disassembled my station in Gwinnett county, and the antenna configuration I programmed, even designed this Automatic Antenna Selector for no longer exists.

The antenna selection logic originally was a bunch of switch statements embedded inside if / else statements -- not very easy to change. I re-coded to use a short table of eleven rows and four columns. The rows represent each band, 160 through 10m, including 60m. The columns are the first, second, third and fourth choices of antennas. Much easier to understand and update.

I expanded on the idea about the Mode button. Originally, it was just primary / secondary. To allow for up to four antenna choices, perhaps there are more than two modes. How does one tell which mode you are in? The mode LED was programmed as just on or off. I could have it be off for primary, blink once for secondary, twice for tertiary, and three times for quaternary.

The last issue was how to test the relay action without having to program a new antenna configuration.  Currently, there's nothing programmed for relay position 4. If one wanted to hook an antenna there to test it, how do we do that without burning a new chip? 

Holding down the mode button could select a special mode that selects ports A0 ad B5. Then, each time you tap the mode button, it would switch: A1 and B4, A2 and B3, etc. In this way, each port can connect to each antenna. And the mode LED would indicate this with a solid on condition. Hiding the mode button again would switch back to the to the normal program.

How about using a radio other than the K3? Maybe I want to use the Novice Transmitter, or perhaps my trusty Elecraft K2/100. Perhaps we re-purpose the seven-position manual selection switch to encode K3 band values. A simple diode matrix would work, and I have a bunch of 1N270 diodes, 

This project is now working, but it is far from done.

W5WVO 6m Beam Project

W5WVO clone construction so far.

I wrote earlier on my purchase at the Dalton, GA Hamfest of the 6m Mystery Beam. It clearly formed some kind of antenna, given the lengths of the elements. But I had no clue how those elements were intended to be positioned on the boom -- and even if I did, I had no idea what kind of performance to expect.

Course of Action

Unsure of what to do, I asked the folks on he SEDXC mail reflector. Joe Subich, W4TV suggested that I use the components to implement the W5WVO modification of the A50-5S, or perhaps re-create one of YU7EF's five element designs for a 4.5m boom or 4.15m boom. 

Choosing between these options was difficult. What I had wasn't a A50-5S, so the W5WVO medication wasn't straightforward. And the YU7EF designed were even further afield from my starting point.

I decided to adapt my tubing collection to W5WVO's design. 

My elements were too short, they'd need to be extended. But, it isn't as simple as just matching the length W5WVO specified -- the taper schedule is different. 

The A50-5S and the W5WVO designs use 48" of 3/4" tubing in the center extended with 5/8" tubing to the element length. My tubing is 3/4" the entire way. I'd need 5/8" extensions, but how long?

Answering that question required modeling.

Modeling a Solution

As a Mac user, I use CocoaNEC with the NEC 2 engine. It's pretty sophisticated, actually, but getting good results requires using the NC modeling language, which can be a bit tedious. 

My first model was W5WVO's design using the normal taper schedule - inner 24" of each half element are 3/4" with the rest being 5/8". Results were very similar to, but not exactly the same as W5WVO's article. (Part of the reason is W5WVO used NEC 4 engine) But what I had was close enough.

Second model used the 3/4" element lengths I had, spaced according to the W5WVO design. The results were akin to the W5WVO, but with significantly worse F/B.

Third model used the same 3/4" element lengths, with 5/8" extensions on the tips of each element. Because of the different taper schedule, I experimented using a different percentage of the W5WVO dimensions. Lo and behold, at 80% extension length, I modeled something very, very close to the W5WVO design. 

Reflector with
5/8" extension.

The extensions needed on each end are short:

• Reflector - 2.5"
• Driven Element - 0.75"
• Director 1 - 1.75"
• Director 2 - 1.375"
• Director 3 - 0.25"

I added about 3/4" for overlap inside the 3/4" tubing. I secured the extensions using 1/8" Cherry pulled rivets. These aren't ordinary "pop" rivets. Ordinary pop rivets are just a hollow aluminum tube. These leave a steel mandrel filling the tube -- a solid, structural connection.

Building

Extensions on each element.

First step involved cutting the extensions and riveting to each element. I used two rivets on opposite sides. On the D3 element, with the very smallest of extensions, I ended up with one rivet because I broke my #30 drill bit. 

Second step would be to hang the elements on a boom. Oh, wait, I need a boom!

The parts I bought at the Hamfest had three segments of 1" Aluminum pipe which was reinforced by a 13 foot piece 3/4" pipe. None of this fit well together. And the diameter was somewhat small for a 20 foot boom.

I had a 7 foot piece of 1-1/2" tubing I replaced on a Cushcraft A3S. I also had a 12 foot piece of 1-1/2" tubing. Together, they would be 19 feet. The last 10" of the 7 foot tubing had a crack, so I cut that part off, and used a  1 foot 1-5/8" tubing section to join the two together. My only hesitation was that the 12 foot piece was only 0.035" wall (whereas the others are 0.058"). I was worried it might not be strong enough. I figured it was worth a try, perhaps aided by a supporting truss.

I also had to figure out a boom-to-mast plate. I was fortunate to have one in the junk box, along with U-bolts that would work.

Mapping the elements onto the boom was a little tricky. The U-bolts just barely fit over the 1-1/2" boom, but they could not go over the 1-5/8" joiner. I had to move the reflector 8" away from the end of the boom so that Director 2 did not fall on the joiner. 

I managed to get all the elements positioned on the boom. Definitely looks like an antenna now.

Next step will be to figure out how to feed this beast with a gamma match.

Hamfest Special - Mystery 6m Beam

Back in July 2021, I asked members of the SEDXC reflector how best to work Europeans on 6m, one important bit of advice was to use an antenna with more gain than my Cushcraft A50-3S. Three elements just won't cut it on marginal paths. The suggestion was to use a beam with five or more elements. 

Such antennas are several hundred dollars new. The A50-3S was used from a local club for $80. Yes, I'm cheap, but it has served me well. Since then, I've been looking for a reasonable, used antenna. I'm even willing to do some minor repairs.

As I was leaving the Dalton, GA hamfest at the end of February, I stopped by a tailgate area where a guy had a trailer load of stuff. I could see a Cushcraft tribander, a Hy-Gain tribander, house brackets, guy brackets, feed lines, a gin pole and other stuff. I wondered if he might have something for 6m. So I asked.

The owner wasn't present, so his kid called him on a digital walkie-talkie. He said he had a 5-element Cushcraft 6m beam. By the time he made it back to the trailer, we pulled it out, and he changed his tune, he said it was a 6-element Hy-Gain beam. You could see the gamma feed on the driven element. 

Sounded great to me. I negotiated him down to 63% of his asking price, and walked away with the antenna bundle for $125. Sweet.

Getting home, before  I took the antenna off the truck, I went looking for Hy-Gain six-element 6m antennas. I found manuals for models 66B and VB-66DX. They are very similar. The VB-66DX appears to be a hardware-update of the 66B design. These antennas are also fed with a beta-match, not a gamma-match. What I bought is not a Hy-Gain antenna.

Taking the antenna off the truck, cutting it apart and laying the pieces out on the deck.What I found was surprising:

• 

  The components I purchased
  

  REF - 3/4" Al - 9' 9" - 117"
• DE - 3/4" Al - 9' 2" - 110" (Gamma match)
• D1 - 3/4" Al - 8' 9" - 105"
• D2 - 3/4" Al - 8' 8" - 104"
• D3 - 3/4" Al - 8' 7" - 103"
• Misc - 1/2" Al - 50" - Swaged to 5/8" last 6" (2) - Hy-Gain bracket adds 1 1/2" - 101 1/2" total
• Boom - 1 1/4" Al totalling 24 feet in three sections with 1" thicker wall inner tubing

First five elements mount with a single 1 3/4" U-bolt and saddle in the center. The Misc segments could mount in a single Hy-Gain bracket, giving a total element length of 101 1/2" -- which might be a forth director.

Gamma match is a total of 16" 1/2", most of which is a 1/4" Aluminum rod. The shorting bar is at 14 1/2". The first 1 1/2" is a 1/2" Al tube flattened at one end for a screw. The open end hid a disc ceramic capacitor that sadly I broke in transit. Looks like a 3-6 kV capacitor, value unknown.

The boom is a piece of work. There are three 1" Al pipe sections: 75 3/4", 144", 68". The 68" section has a 156" piece of 3/4"Al pipe with a ticker wall as reinforcement. It is mounted asymmetrically, so more of the end extends into the 144" piece than the 75 3/4" piece. There is no boom to mast bracket.

I'll note that the boom is aluminum pipe. Not tubing. It's designed to carry liquids, not be structural.

Clearly, this is not the parts to a Hy-Gain nor a Cushcraft 6m beam. First off, no commercial 6m beam ships with single-tubing size elements. They all use a taper schedule. There are two good reasons for this. 1) It makes the antenna adjustable. 2) they can ship sections shorter than 7 feet, which allows the package to go UPS, 

These parts are a collection different ideas. The U-bolt mounting is Cushcraft-style, but the boom size is too small for a Cushcraft. The boom is 24 feet long, but it is clearly not a Hy-Gain. The boom is way too small, since Hy-Gain used a 2" boom. Plus, it apparently had a truss (now broken), probably because the    for the 24 foot length.

What I appear to have is a collection of parts used to cobble together a poor imitation of something like the Hy-Gain 66B / VB-66DX. Not at all what the guy at the hamfest told me.

There's plenty here to put together a solid five element beam on a 12 to 18 foot boom. The elements are already cut. The hard question is how far should they be spaced? Once I know what the right spacing is, I would then know how much boom I need. 

The broken gamma match is annoying, but fixable. Once I know where to place the elements....

This project is going to take some work.

The Challenge of a New QTH

A decade ago, my wife and I spent four years in Floyd County in one of her church postings. We loved the area, and imagined we'd retire there.

In November we took the first step. Bought a house in Floyd County near Rome, GA. House is on the top of a small mountain - Ward Mountain, rising 300 feet above the valley floor below. From the front porch, there is a gorgeous view to the West. On a clear day we can see 35 miles to Lavender Mountain, which is practically in Alabama,

The house is a little smaller than we'd like at 2100 square feet, but there's over 11 acres of land. A small office outbuilding with one room and a tiny bathroom has become the ham shack.

We've owned the house in Gwinnett county for 30 years. Now we are transferring things to the new house. There's a lot to do. We'll sell the Gwinnett house in the next months. In the meantime, I'm focused on building up the Floyd QTH when I have the energy.

Antennas are the first order of business. I first put up an 80/40/20m Trap Dipole. It's up about 12m in the trees. I erected a 160m Inverted-L with two elevated radials. It's a bit noisy, so receiving antennas are likely needed to make the most of that. I plan for three beverage antennas. A 6m dipole barely 4m up in the trees offers me an option on that band.

I've also put together the HF4B. I've mounted it on a 19 foot pole lashed to a deck post. It needs adjustment to work well. It's OK on 10m, but 15 and 20m aren't quite right.

I'm planning to put up a tower. I'll need to take down the tower in Gwinnett first. My plan is 70 feet of Rohn 25, with the A3S/A743 on top. 35 feet below that will be an A3S, pointed at Europe. This would give me a stack toward Europe, plus coverage in other directions with the top antenna. Horizon is unobstructed in every direction except to the NorthEast, where the two additional summits of the Ward Mountain chain are. Those peaks are just 100 feet and 140 feet higher, but they are 1 km and 2 km away, respectively.

I'm already seeing good results with the 80/40/20m trap dipole. There are benefits to being on the top of a mountain. Even a simple tower should be awesome.

For 6m, I'm on the lookout for a 5-6 element beam. The Cushcraft A50-3S i've been using in Gwinnett just doesn't have enough gain to work the intercontinental paths. 

On the office building, I've already moved in an operating desk with desktop shelves, and another luncheon table that serves as a workbench. The main part of the floor is a little more than nine feet square, And almost six feet of the rest of the building is split between the tiny bathroom and the rest of the floor. The desk and workbench are a bit of a squeeze.

A wire shelving rack takes up some of the space opposite the tiny bathroom, and gives me room to store things. I don't know how I'm going to get a whole basement of ham gear into this little building.

Such is the challenge of a new QTH.