Saturday, September 19, 2026
Cancer and my Absence
Friday, May 1, 2026
Retirement Project: SWTPc 6800 (with 6809) Resurrection
In 2022, I documented my ancient SWTPc 6800 Computer System, which I had upgraded with several home-brew cards. It had been 25 years since I had last used the computer, but this ancient machine fascinated me. I wanted to record what I had done, as I'd forgotten a lot.
During this process, I plugged in one of the I/O cards incorrectly -- off by one pin. Normally, there's an index pin that prevents this, but some of my cards don't have the plug that blocks the pin.
Sadly, when I powered it on, smoke was immediately released from one of the chips. After correcting that board, I found the system completely inoperable. This computer was 45 years old at the time, and I had many other projects that needed more attention. I decided that fixing it would be something I could do in my retirement.
And, it remained broken until this year. You see, I've retired, so it was time debug this monstrosity.
When I originally built the CPU boards for this machine, I borrowed a 32-channel HP Logic analyzer. That allowed me to fix the bugs in the hardware and the software alike. But I long-ago lost access to such equipment. I had little more than the original kit manuals, schematics and notes, plus a digital voltmeter and an oscilloscope.
Symptoms
Debugging
- +8v: +8.3v
- +12v: +14.15v
- -12v: -14.06
- RESET* - goes low for 0.1-0.3s, then high
- HALT*, BREQ*, MRDY, NMI*, IRQ*, FIRQ* -- all staying high.
- BA, BS - both low -- this means that the CPU is actively controlling the bus
- E* and Q* - these clocks running at 2 MHz, as expected, this mean the CPU was alive at least
- VMA* - cycling, meaning the CPU was attempting to access the bus
- R/W* - cycling as expected
- D0*-D7* - each data bus pin showed signs of normal activity
- A0-A15 - the Address bus had problems on two pins
- A3 - activity limited to 0v to 1v
- A14 - activity stuck around 0v
Next Steps
Thursday, April 30, 2026
Claude Helps with the Automatic Antenna Selector
| Automatic Antenna Selector |
This cable connects the Auto Antenna Selector to the AUX port of a K3. I bought two of these a couple of years ago, and I easily found one. But the second one eluded me. Without it, I couldn't test the Selector in Design C (Dual Radio) mode. I had done all my testing in Design B (Single Radio) mode.
Having the proper cables, I did my testing and found several bugs. Some of them were going to be difficult to fix. Part of the problem was my approach. I had organized my antenna selection table by the selections, then by band. This made it difficult to determine the choices available per band. So, I organized the table by band, then listed the choices. From this, I could determine which choices were available for a given band, skipping over those that would conflict with an existing port.
This greatly simplified the code for making the mode selections, which are very different in Design B (Single Radio) and Design C (Dual Radios). In Design B, the first selection is assigned to the first port, so there can only be three additional choices. In Design C, only one port is selected per radio, so we can potentially use all four selections (so long as there's no conflict with the other radio).
Design C bugs were all addressed, and Design B worked better than ever.
Before I retired, I'd been messing around with Anthropic's Claude Code. I was curious what Claude might think of the firmware, so I requested an in-depth code review.
Claude Code came up with a number of good suggestions. It found some dead code, made several type suggestions, a minor code re-organization, and way better comments.
What impressed me, though, was that Claude Code had a deeper understanding of the particular PIC processor that I did. It suggested I turn on the Watch-Dog Timer (WDT). That I change how Timer 0 (TMR0) was used. And, that I use the PMD register to power-down the modules that I wasn't using in the device.
I thought I was using TMR0 correctly. And I knew about the WDT, I just didn't think it was necessary. But the PMD register I knew nothing about. All of these suggestions seemed like a good idea to me, so I made them.
All in all, Claude Code did eight rounds of review of this code. It made a couple of suggestions that I knew were wrong, and it took corrections well.
The next day, I burned a chip and plugged it in the unit for testing.
It bricked, Nothing. Not even a single flash of the LEDs on startup.
Somewhere in the midst of Claude's suggestions, we had changed the software in a way that it no longer worked at all.
I made a new branch of the code and backed out some suggestions. I determined it had nothing to do with the WDT or PMD register. That left something amiss with TMR0. This could be a problem with Microchip Code Configurator (MCC).
I had switched TMR0 to use the HFINTOSC. It was programmed to generate an interrupt every 5 ms. Except it didn't work. I switched it back to us the LFINTOSC, also programmed for every 5 ms, and it worked as expected. I'm not sure why it didn't work with the HFINTOSC, but having several oscillators gives one options. I'm happy it works.
Once it was working again, I walked through all of the Design B and Design C test scenarios. Everything worked with flying colors.
AI is certainly useful, even for amateur radio projects. Just don't blindly trust it. Remain in the loop for all changes.
Sunday, March 22, 2026
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.
Saturday, February 21, 2026
Rx Antenna Controller
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| Rx Antenna Controller is QRV. |
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
Putting It Together
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| Remote relay box |
- 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;
What's Next
Wednesday, February 4, 2026
Beverage Controller
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| Remote and controller boxes laid out for wiring. |
Design
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| Test positioning the Controller |
Construction
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| Remote mounted on SPG |
Debugging
Tuesday, December 30, 2025
Beverage(s)
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| View 175 feet down NW Beverage. |
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
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| Beverage terminators (above) and transformers with F-connectors (below) |
Transformer Boxes
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| 500:75 ohm transformer |
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| Transformer assembly progression |
Erecting
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| Single wrap traps wire |
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| Installed insulator |
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| Terminator installed |
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| Tension connection |
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.












