Polishing Up the Rx Antenna Controller

Many software projects are never fully complete, as there's always something to add with a small change to the software. The Rx Antenna Controller isn't any different. 

The initial version of this project was basically done. But pressing the antenna selection buttons resulted in a response on the serial port. This could cause problems with computer control if the response was not anticipated.

I added a new command: &AI; and &AIn;. This gets and sets the Auto-Info mode, respectively. With &AI1;, pressing an antenna button results in an &ARn; response on the serial port. &AI0; turns off Auto-Info mode -- button presses do not result in a serial port response. The default is &AI0;.

I"m very happy with the way this project has turned out. While I have ideas for a Version 2, it mostly involves hardware changes to the remote switching box to allow selection of the AUX antenna for diversity reception.

Rx Antenna Controller

Rx Antenna Controller is QRV.

I started building this unit a couple of months ago. I called it the Beverage Controller, because my motivation was to select amoung the three Beverage antennas I had erected. Yes, I've managed to erect three 500 foot Beverages, one to the NE, SE and NW.

Performance of these antennas is convincing -- 1-2 S-units lower noise than the inverted-L or dipole antennas I use on 160 and 80m, respectively, plus a directional signal boost if the beverage is pointed in the right direction.

I discussed my design issues with this unit in the previous article. Debugging the serial port took another month.

Serial Port Debugging

The reason I had chosen the PIC16F18426 for this design was because of the built-in EUSART. Receiving worked just fine. I could send commands to the controller and it would act on the commands. But it sent no response. 

I had configured the PIC to use RC5 (pin 5) for the EUSART receive input, and RA5 (pin 2) for the EUSART transmit output. After a bit of troubleshooting, I found no action on RA5. It remained at 4.5 V the entire time. Was this a wiring problem, or a programming problem?

I ended up writing another PIC project and setting up a chip on a solder less breadboard to solve this. This project simply sent "Hello World!" at 300 baud every 5 seconds. It also drive two LEDS on the C port pins. The LEDs which alternate during a 1-second startup. When transmitting, the second LED would light up. 

My serial test project worked perfectly. LED 2 flashed for about 1/2 second every five seconds, just as expected. So, why didn't the beverage controller project work?

I modified the beverage controller project to also send "Hello World!" every 5 seconds. Except it didn't work. I traced the wiring in the controller head. RA5 was connected to the MAX232E pin 11. It was the MAX232E that was driving the pin to 4.5 V. With the MAX232E out of the circuit, RA5 stayed at 0 V all the time. It was like the software had configured RA5 as an input, not an output.

I got to the point that I could test both projects on the solder less breadboard. I even programmed the same chip with the serial test project -- and it worked. Programmed the same chip with the beverage controller project -- and it didn't. This was definitely a programming problem.

I tried several modifications of the configuration, eventually applying the serial test project configurations to the beverage controller project. At some point, it started working. I still don't understand what I changed to make it work.

Putting It Together

Remote relay box

After such a struggle, I was happy to finish. I re-programmed the chips to send and receive at 9600 baud. This is plenty fast enough for this purpose.

The controller supports one Kenwood/Elecraft-style command, which takes two forms - a Get and a Set operation:

• Get - &AR; -- responds with &ARn; where n is 1 through 5
• Set - &ARn; where n is 1 through 5 -- selects the antenna specified by n, responds with &ARn;

With the serial port transmit working, I could remotely interrogate the controller to determine which receiving antenna was currently selected. And selecting an antenna would respond to ensure that the controller had received my command.

The controller mounts nicely on the equipment shelf. I used some temporary stick-on labels until I find my computerized label-maker. 

What's Next

The current firmware sends an &ARn; response when a button is tapped. I probably need to make that configurable with a serial command.

I've also thought about adding a scanning feature. The controller could automatically switch antennas after a few seconds. Holding a button could add/remove that antenna from the scan.

However, after a couple of months of using the controller, I've found a glaring deficiency in my design. The Rx Antenna Controller only selects one antenna for the RX ANT port. I use a broadband splitter to also connect to the AUX port for diversity reception. But this only permits diversity reception of one receiving antenna against the transmit antenna. I can't do diversity reception between two receiving antennas. 

What would be nice is to have the remote relay box select the antenna for the RX ANT and AUX port. This would require twice as many relays and a way to control them individually. Doing this requires a re-design of both the remote relay box and the controller box. 

Beverage Controller

Remote and controller boxes laid 
out for wiring.

With these Beverage antennas, I needed a way to switch between them quickly and easily. 

Taking a cue from the K9AY Controller, I didn't want to just hook up a rotary switch. I wanted a push-button controller. Plus, a lot of the time I'm remotely operating my station on FT8 from the house, I wanted that capability as well. 

Design

I planned for at least three Beverages, maybe more. Plus I had the K9AY loops. That's at least four antennas, having a fifth would give me a spare.

The buttons and indicators needed to be convenient to operate, up front in the station without being intrusive. 

The receiving antenna feed lines also needed to terminate at the Single Point Ground (SPG). Best option was a remote relay box to do the switching, and a small controller box containing the buttons and indicators.

Test positioning the Controller

Adding a serial port to the controller allowed the antenna selection to be interrogated and selected. I already the PIC16F18426 chips on hand. This 14-pin device has a built-in EUSART. A MAX232 would handle the RS-232 level conversion.

Construction

I found a small Bud box in my junk box for the remote. I ordered a die-cast aluminum box for the controller. It was small, but it fit very nicely up under the shelf supporting the P3. Convenient and unobtrusive.

Remote mounted on SPG

The remote has six RF connectors - four F-connectors for the Beverages, one BNC for the K9AY, and another BNC to connect to the K3. SPDT relays are used. When selected, the relay connects the antenna port to the K3 port. When unselected, an appropriate resistor connects across the antenna port. ( I used 82-ohm resistors for the F-connectors, 51-ohm for the BNC -- closest I had to 75 and 50 ohms, respectively )

I used 12 V relays. Unlike the KK1L 2x6 Antenna Switch, I didn't want to activate each relay with a separate line for +12 V. Instead, I sent +12 V to the remote box on a common conductor and then returned a signal for each relay to be grounded by the open drain pins on the PIC. 

This lead to a design problem. The PIC doesn't support true open drain outputs. Each pin is clamped to Vdd, which in this case is +5 V. That left about 6 or so volts across each relay, pulling them all in. 

To solve this, I added 2N3904 NPN transistors to the relay box as open collector drivers for each relay. A 3 K resistor connects the base of each transistor back to the PIC. Instead of a logic 0 activating the relay, a logic 1 does the same job.

The controller box is really tight. I borrowed five switches from the K1EL Keyer. The LEDs and switches barely fit. The controller itself is simple. Five RA port pins connect to the pushbuttons. Five RC port pins drive the LED indicators and NPN relay driver. One RA pin and one RC pin communicate with the serial port. 

Changing the sense of the relay switching required re-wiring of the LEDs. Before, they were tied to +12 with the cathode of each LED brought to ground by the PIC. Except that didn't work due to the design problem. Instead the cathodes went through a common 330 ohm resistor to ground, and the anodes were connected across the activation lines for each relay.

Debugging

I debugged this design in parts, starting with the controller box, then the relay box separately. Once I connected them together, I found the design problem that required much re-wiring. 

The button selection worked great. The serial port has been more of a problem. While the PIC receives commands correctly, it doesn't appear to transmit anything at all. It is a puzzlement. 

Beverage(s)

View 175 feet down NW Beverage.

My initial experience with the 2024 ARRL 160m contest demonstrated a serious noise issue on Ward Mountain. The Inverted-L showed an S4 noise level. I needed low-noise receiving antennas.

I'd had some success with the half-size K9AY loops at the Gwinnett station. But I could use something better.

At contest stations such as NQ4I or WW4LL, I've had the opportunity to use Beverage antennas. But  never at my home station.  I planned to change that. 

The Plan

Having a bit of acreage, there's room for several beverages.The key directions were to the NorthEast (NE), SouthEast (SE) and NorthWest (NW). 

For 160m Beverages, many recommend at least 550 feet of wire, minimum. This is just a bit over one wavelength long. ( Technically, using a velocity factor of 95%, one wavelength of wire should be 520 feet at 1.8 MHz ) Since they don't make spools of 550 or 520 feet of wire, a 500 foot spool should be sufficient. 

Wire is expensive. A 500 foot spool of stranded 14 gauge THHN wire is $78 at Home Depot. 

Beverage antennas are pretty simple. The long piece of wire is fed against ground at both ends. The near end uses a matching transformer to adapt the nominal 500 ohm impedance of the Beverage to a feedline. The far end contains a terminating resistor. 

Beverage terminators (above) and
transformers with F-connectors (below)

Terminator Boxes

I built five Beverage terminator boxes using a 470 ohm 2W resistor (OY474KE Ceramic composition resistor) and a 75v gas discharge tube.

These parts fit snugly in a small plastic box. Thumbscrews make for easy connection to the antenna and ground rod.

Transformer Boxes

500:75 ohm transformer

Beverage transformers are wound on BN-73-202 cores. Primary is 3 turns using red wire-wrap wire. Secondary is 8 turns yellow wire-wrap wire. The primary and secondary are separated using cut off bits of plastic stirring straws. The 3:8 turns ratio is a good match for 75 ohm coaxial cable used to feed the antenna. 

Transformer assembly progression

Transformers are housed in the same small plastic boxes. An F connector jack supplies the transformer primary. Transformer secondary connects to thumbscrew posts with another 75 V gas discharge tube across them. There is no common ground connection between the primary and secondary -- this avoids noise pickup from the feedline. 

Thumbscrews connect to the antenna and ground rod at the feed point.

I built four transformers initially. The small plastic boxes work necessitated a bit of ingenuity to get everything in place. 

Erecting

Single wrap traps wire

Installed insulator

Being surrounded by forest, the Beverages are suspended from trees aligned with the reception path. Screw-in electric fence insulators are used to support the antenna about 8 feet off the ground. 

A rope around a tree supplies modest tension for the wire at each end. This leaves the ends relaxed to connect to the transformer or terminator boxes and ground rods. 

The technique for installing the beverages is straightforward, I start by locating the feed point transformer near a supporting tree and mounting an insulator there. Once the ground rod and tension rope are installed, it's a matter of going from tree to tree installing insulators and hooking the wire. This continues until you reach the end of the wire, where the ground rod, terminator box and tension rope are located. 

Terminator installed

Tension connection

At the transformer and terminator, the wire to the ground rod zig-zags a bit to take up the slack from the insulator. This keeps the plastic box from flapping around in the wind.

Every attempt is made to keep the Beverage straight toward the target heading. A bit of direction change to make supporting trees is tolerable. I used the iPhone Compass app to keep me on heading. 

At my location, the terrain slopes a bit. For the NW beverage, after the first 175 feet, the drop-off is quite gradual. 

The NE beverage is another story. Terrain drops about 10 feet in the first 200 feet, but the last 300 feet drops about 80 feet. The beverage terminator ended up in the bottom of a deep ravine. Navigating the slope was quite difficult. Rocks, branches and other debris on the forest floor made for tricky footing. Be careful out there.

Feed Line

I caught a deal on some RG-6. I found 700 feet on a spool for less than $20 at the Dalton, GA hamfest. RG-6 is cheaper than stranded wire. A 500 foot spool is $50 at Home Depot. This 75-ohm coax makes for a good receive antenna feedline. It's cheap, low-loss and easy to match.

Performance

Only have a little experience with these antennas. NE Beverage has been up a month, and the NW Beverage a week. 

Performance is amazing. 

On the 160m Inverted-L, there's typically S4-5 noise. Noise level on the Beverage antennas varies depending on the time of night, but is typically 1-2 S-units lower. 

More importantly, signal levels are stronger. If I watch the Elecraft P3 panadapter, switching from the Inverted-L to one of the Beverages, the noise level drops somewhat, but the signals rise above even more. Sometimes, when there are no visible signals on the Inverted-L, many are Q5 copy on a Beverage.

Further, switching from one Beverage to the other can have a dramatic effect on signals. Sometimes, signals that are strong on one are inaudible on another. Other times, signals are about the same.

In short, the Beverage receive much better than the Inverted-L. During the recent Stew Perry TBDC, I listened on the Beverages almost exclusively. 

They 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.

Re-writing the K9AY Controller

 I was quite happy earlier this month to get the K9AY Loop Controller working. After using it in the ARRL 160m contest, I decided I needed to make some changes to the firmware.

That presented a problem. You see, while Microchip has made some excellent developer tools available for their PIC series of microcontrollers, like all software, it is updated from time to time, and things change.

When I used MPLAB X three years ago to write the controller firmware, I used the PIC assembly language tool MPASM. That was with version 3 of MPLAB X. I recently updated to version 5 of MPLAB X, and MPASM was no longer supported. Instead the new assembly tool was called pic-as. And, of course, it was syntactically different than the old MPASM.

I made an attempt to edit my existing code into something acceptable to pic-as. While I got it to build, I found it didn't run correctly. Rather than try to debug, I figured it might be easier to start over.

Microchip has a good C compiler. I decided to start there. I'm well experienced with C, but this left open a lot of questions. The PIC has a number of configuration registers that must be set at startup. How does one do that with C? 

This actually turned out to be very easy. Microchip has a tool called the MPLAB Code Configurator (MCC). It provides a number of graphical tools and wizards that specify the chip configuration, down to the pin assignments and interrupts. MCC then generates the appropriate C code. This is a good thing. One of the hard parts of working with the PIC is figuring out how to set all the internal registers. MCC does this part for you.

My second question had to do with interrupts. How do we process interrupts in a C program? This also turned out to be easy, because MCC generates code to handle interrupts, too. When properly configured in MCC, one need only write a simple void function to process the interrupt. My controller uses a timer interrupt every 2 ms to check the state of all the buttons and update the LEDs and relays appropriately.

Re-writing the controller program in C ended up taking less time than figuring out the assembler syntax changes between MPASM and pic-as. 

And the best part is, it worked! 

K9AY Controller and Antenna

K9AY Controller at operating position.

In 2007, I put up some K9AY loops. They were a little less than half-sized, about 33 feet in each loop. They worked pretty well on 80 and 40m, although they were a little weak on 160m. After about three years, they stopped working. At the time, I was using a rotary switch to change directions, but I really wanted a push-button controller.

In 2015, I designed a controlled based on a 74LS175 Quad D-type flip-flip. It was pretty simple in concept, but, it didn't work. The bounces from the switches changed directions rather randomly.

Which lead me to write this article, about a solution - using a PIC micro-controller to solve the bouncing switch problem. 

I built that prototype, and wrote about it three years ago. One problem was that the wiring appeared flaky, it wasn't always dependably switching. I figured I needed to design a PC board. 

While I've been working on that, I had a thought a couple of weeks ago -- maybe I could piggyback a second piece of perfboard to my prototype and keep the board from flexing, and that would avoid the flaky wiring. Easy enough to try.

K9AY Antenna box
at base of tree used as
support

Sure enough,  doubling up the perfboard helped. I determined that the wiring wasn't that flaky. Part of the problem was that the NW and SW switches and LEDs were reversed. Pressing the SW button sent the NW voltage, and vice versa. 

With that fixed, I couldn't find any reason not to put the K9AY back up. I used 42 feet of wire in each loop. This is a good compromise length for 160, 80 and 40m. 

Some on the air testing shows that it works pretty much as expected, and the push-buttons make it really easy to change directions.