The fascination in seeing how far our signal can go is part of the ham radio experience. WSPR is a way to do it with low power and little effort from the operator.
I discovered and built the Ultimate 3S from QRP Labs. I obtained the full combination including a multi-band switched relay board for its low pass filters, GPS and enclosure. Not too many days later the main kit arrived from the far east, and the enclosure not too many days afterwards.
The main board includes the microcontroller and a BS170 power amplifier, and not much else. A daughter board is a synthesizer that can operate from LF to VHF. A single low pass filter plugs into the main board. The kit can be used in this fashion, or the relay board can be added to permit easy band selection – and even setting the unit to transmit in sequence on multiple bands.
Connected to my WM-2 power meter – the U3S is outputting 300 mW on the lower bands, around 200 mW on 30 and 20 meters, and 100 mW on 10 meters. How far can this thing reach? Europe is routinely reached before dusk on 30 meters, and around dusk and after on 40 meters. One morning it reached Australia on 30 meters – and this is in mid-summer! It should do even better in the fall and winter. My judgment is that this is enough power for WSPR where one has a reasonably effective antenna (here I am using verticals on 80 to 30 meters). More power results in more QRM to other users of the spectrum and seems unnecessary. I may consider an amplifier for 160 meters knowing the inefficiency of my short vertical.
Few issues in the build – the modular construction with boards that plug together works nicely. Conquering the instructions to use the device – well more careful reading is required than my initial readings. I needed just a little help from the QRP Labs Reflector https://groups.io/g/QRPLabs — including getting some needed tips from other messages there. I may post some tips in a follow-up entry someday here. Once programmed, easy to select the operating band(s).
On the GPS – very cool. Without it, the time must be manually synchronized to within +/- about 1 second of the world’s atomic clocks. It can be done …. but plug in the GPS -and each time it is powered it takes just a minute or two to set the clock. The GPS module is made to use remote from the U3S case – mine sits on desktop near a downstairs window – it works wonderfully. Cool to see your latitude and longitude, along with the time, displayed when the GPS synchronizes the U3S. The white raised object on the board is the patch antenna to receive GPS – the electronics are on the lower surface (along with 3 LED indicators I mounted on the wrong side – no worry I can see their flash – and the U3S display itself tells me when the GPS is locked on.
This view also shows the construction – the LCD in the front, above this the main board (a single toroid can be seen which is the transformer at the output of the PA. The synthesizer is to the left and a low pass filter (this one is 30m) on the right. Finally the relay board with 4 of the 5 LPF filter slots occupied. The two push buttons are for commanding the U3S. At the other end the DB9 is to interface with the GPS, and the DC power connector (5 volts) and BNC RF output. The well-crafted case has space for expansion.