Some time ago I build the Ultimate 3S QRSS/WSPR transmitter from QRP Labs. It came with one low pass filter. I chose the 10meter LPF because I was originally thinking of using the beacon transmitter for the SOARA K6LLL 10 meter CW beacon and the U3S is a great fit for that job. Once I decided to use the transmitter as a WSPR beacon, I needed more bands!
Automatically sending out WSPR beacons on different bands requires the Ultimate relay-switched LPF kit. In order to automatically set location, date/time and calibrate the output frequency precisely, I also purchased the QLG2 GPS Receiver Kit.
The GPS kits’ SMD parts were already soldered down to the board so all that was really necessary for this kit was to solder on the SMA connector and mount the board into the U3S chassis. There are four signals that interface it to the U3S main board. There is no predefined mounting location for the GPS, so I mounted it on standoffs with the SMA antenna connector protruding through a hole that I made in the back cover. It’s a tight fit with the 5V buck converter I had installed previously.
Building the low pass filters requires winding three toroids for each filter and installing matching capacitors for the band you’re building them for. For each board, I installed the capacitors, wound the three toroids and installed them into the LPF boards, and then installed the connectors. I tested each LPF board using my Rigol spectrum analyzer.
Building the LPF carrier board consisted of installing 5 relays, 5 diodes, connectors that mate with each LPF board and the connectors that attach the Relay switch LPF board to the main U3S board. On the revision 5 board, there were also quite a few jumpers that needed to be installed. It is very important that you follow the correct instructions for the version of board you’re building with all of the QPR Labs kits.
Output power varies by band with 40 meter having the highest output power of about 400mW and 10 meters having the lowest output power of about 100mW.
Once completed, I was able to get everything integrated and working. After configuring a “mode” setting for each band, I set it on its way beaconing. The GPS was able to get a location fix quickly even with the antenna inside the house. Having a GPS means I no longer have to configure time precisely or adjust the reference frequency of the 27MHz oscillator crystal on the Si5351A module manually.
Initially I wasn’t being heard by anyone. I quickly figured out that I had adjust the frequencies I was using to be between the lower and upper band pass frequencies for each band. After that, I was being heard on milliwatts!
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