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.

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. See hiqsdr.org and technologie2000.de.

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.