Jim Ahlstrom

PC board image

Hardware Projects

These are my published hardware projects. I use KiCad and Eagle to design printed circuit boards. I have given up using pre-sensitized photographic PCB material. Instead I have boards made by OshPark. I prefer surface mount devices because I do not have to drill the holes. It is faster to solder them, and the zero lead length makes the RF design more robust.

How to Connect a Key to a PC

Here are some circuits for connecting keys and switches to a PC using a USB to serial port adapter or a microcontroller.

Filter Board for Hermes-Lite2

I am active in the Hermes Lite project. Steve Haynal, KF7O, and a group of interested amateur radio operators are working to develop a direct sampling Software Defined Radio transceiver. The transmitter has a push-pull MOSFET output at five watts. But transmit filters are required if this is connected to an antenna. My filter board is 5x10 cm, and fits in the standard enclosure. It is completely controlled by Hermes-Lite.

Input/Output board for Hermes-Lite2

This project is a 5 by 10 cm printed circuit board and related firmware. The board mounts in the same box as the Hermes Lite 2. It mounts above the N2ADR filter board if one is installed. The filter board and the IO board are independent of each other. The PC running the SDR software sends the transmit frequency to the board. The microcontroller on the board then uses the board's switches to control an amplifier, switch antenns or transverters, etc. There are a variety of IO resources available and there will be different microcontroller software for each application. The IO board is meant to be a general purpose solution to control hardware attached to the HL2.

SSB/CW Transceiver

My SSB and CW transceiver is my current Ham Radio station. It is based on an FPGA surrounded by an Ethernet controller, an ADC and two DAC's. The receiver digitizes the antenna voltage, and the transmitter uses direct digital conversion to RF. There are no analog mixers. This project was published in QEX magazine in the Jan/Feb 2011 issue. An improved version called the HiQSDR is available as a kit or a completed unit.

SSB/CW Exciter

My SSB and CW exciter is also based on an FPGA. The design is entirely digital. The output is generated by a DAC and there are no analog mixers. For SSB, audio data from the PC is sent to the exciter using Ethernet. For CW, the key connects to the hardware, the FPGA provides a shaped carrier at the output frequency, and the PC is only used to provide a sidetone. This project was published in QEX magazine in the May/June 2008 issue.