For the past month or so I’ve been playing with the Ultimate3 QRSS/WSPR kit developed by Hans Summers. The kit originally started as a QRSS beacon, but with its 3rd revision has developed into a robust platform for various weak signal modes. The best part is that it’s inexpensive at around $30. The kit uses pluggable low-pass filters to allow for multi-band operation. When ordering the kit you get your choice of one low-pass filter, but additional filters are only about $4 each.I ordered the kit along with a low-pass filter for 20m. At the same time I ordered additional filter kits for 10m and 40m.

Building the kit is straight forward and the instructions provided by Hans are clear and concise. Total build time was approximately 3 hours. Most of that time was involved in winding and installing the 9 toroids for the 3 low-pass filters. It took me an additional hour to make a case for the finished kit using a small Radio Shack aluminum enclosure. I also built a small circuit on a piece of perf board to provide a stable 5v using an LM7805 and installed that in the case.

After building the kit the next step is calibration. For WSPR it’s important to have an accurate time and a stable transmitter. The Ultimate3 has the ability to use an external GPS receiver to set the time via a serial connection and to calibrate its frequency via a PPS signal. I have used an old Holux GPSlim 236 device that has serial output. For the serial time data I wired a 3.5mm stereo jack to the proper spots on the Ultimate3 board and put a 3.5 mm stereo jack at the end of a mini USB connector. Once the GPSlim locks the time is set on the Ultimate3. The 5V provided by the Ulitmate3 will also keep the battery in the GPSlim charged.

The GPSlim device I have lacks a PPS output so I needed to manually calibrate the transmit frequency offset. I did this by using the method outlined in the Ultimate3 documentation. I used my Yaesu FT-450 along with Argo. The method is straightforward, but I’m finding that my frequency tends to drift up and down about 10Hz. It stays stable enough to have little to no drift during WSPR transmissions, but moves around though out the day. The prevailing thought is this is due to the temperature sensitivity of the DDS module. The PPS calibration method fixes this problem by repeatedly using the PPS as a method to trigger a frequency counter routine and adjusting the frequency on the fly.

With everything built and calibrated I put the little guy on the air. Most of my initial testing has been on 20m. I put in my call sign, a frequency within the 20m WSPR area, and set the transmission to occur every 10 minutes on the 4th minute. The last setting for WSPR is a power level in dBm. Since the stock Ultimate3 at 5V outputs around 150-200mW I set the power level to 23dBm.

I’m not completely done tinkering with this guy. I’d like to fix thed rift problem by getting a GPS unit with proper PPS output. I’m also going to cleanup the internal wiring some and replace those awful Radio Shack buttons. But for around $50 total this has been a pretty fun little piece of kit.