After about one and a half months of carefully soldering, assembling, winding toroids, checking joints for shorts with a DVM, fitting everything into and onto the enclosure, and wiring it all together, my Ultimate3S WSPR transmitter (U3S) from QRP Labs is finished. The U3S is a standalone WSPR transmitter not needing any PC to generate the WSPR signals. It's only sold as a kit. The U3S can also transmit in various other modes like JT9, CW, Hellschreiber, and Opera, but most users will use it to transmit WSPR beacons with it though. The U3S can be programmed to transmit a WSPR beacon for instance every 10 minutes. You can leave the transmitter on, go to sleep, do some chores, or whatever, and later check on WSPRnet.org where your signals were heard. It's great to study propagation, do antenna experiments, or just for the thrill of it, to see how far your 250 mW beacons are able to reach. I will not go into explaining the technical and operational details of WSPR here, as this information can be found in abundance elsewhere on the internet.
I bought the following from QRP Labs:
- U3S QRSS/WSPR Transmitter kit
- QLG1 GPS Receiver Module kit
- Low Pass Filter kit 40m
- Low Pass Filter kit 20m
The remaining components I needed for this project, I already had lying around, things like bolts and nuts, wire, buttons, switches, various connectors, and a still virgin plastic case.
I wanted to keep it simple and low cost. The latter is also one of the reasons why I didn't order the special QRP Labs U3S Enclosure kit. The QRP Labs case looks really smart, is pre-drilled, and the kit also contains all the needed screws, spacers, buttons, switches, and connectors. So I must admit that I was tempted to buy the case kit, but since I wanted to have the GPS module (with onboard patch antenna) and U3S fitted together in one enclosure, I had to find another solution anyway as the aluminum case of QRP Labs would prevent the GPS signals from reaching the patch antenna.
In order to increase the chance of the project being succesful, I wanted to keep it as simple as possible. That's why I also chose not to order and install the Relay Switched LPF Board kit. This means that now everytime I want to change band, I have to manually plug in another LPF. It's not a big problem, as the plan was to mainly focus on the 40m band anyway. But still I must admit that now that everything is working ok, I regret a little that I didn't buy the Relay Switched LPF Board as well, as with it installed the U3S can be programmed to automatically switch bands, and to automatically transmit in a specific band sequence of your choice.
To simplify LPF switching, I'm now thinking about making some changes and placing the LPFs in their own small case and connect it to the antenna connector on the outside of the main case, instead of plugging it in on the transmitter circuit board inside.
After powering up and switching on the U3S for the first time it came alive directly! It was an exciting moment, as with my soldering and kit building skills, it might have sent only smoke signals instead. After adjusting the contrast of the LCD screen, it read "Diagnostic Mode" which was a good sign! The LEDs of the GPS module started pulsing, indicating the presence of serial data bursts and a 1PPS signal, and after clearing the "Diagnostic Mode" screen, soon GPS data with the correct latitude, longitude, and altitude appeared. I was ecstatic; so far everything was working perfectly!
Now I still had to go through the learning curve of how to operate the U3S, which took me quite some time. Once I had the U3S transmitting, I adjusted the PA bias with the help of a Diamond SWR / Power meter. I had programmed my callsign, and the GPS had synchronized the time and automatically set the correct grid locator. But still no spots were appearing on WSPRnet.org.
More transmitting cycles followed, all without success. After each transmitting cycle a calibration cycle follows during which with the help of the GPS 1PPS signal the transmitting frequency is calibrated. I decided to start listening to the signal of the U3S on my Yaesu transceiver in CW mode with a 50 Hz digital filter, and I found out that the U3S was transmitting outside of the 200 Hz wide WSPR band.
I just needed some more patience. I didn't expect that the initial calibrating would take such a long time, and I didn't know that it would need more than one cycle. After reading the manual a bit better and making some changes to the calibration settings in the U3S menu, speeding up the initial calibration, with every transmitting and calibration cycle, I gradually saw the U3S signal getting closer to the WSPR frequency segment of the 40m band.
And then suddenly there it was, more than 20 spots for PA7MDJ, from all over Europe! The next night the U3S and a simple end-fed half-wave wire antenne even managed to get my 40 metre WSPR beacons across the Atlantic to various US States including Florida. The fact that it's just a power of about 250 mW and a transmitter that you built yourself gives it all an unexplainable sense of satisfaction.
 |
| The first results |
 |
| Day one |
 |
| Crossing the Atlantic on the second night |
The U3S needs a 5 V power supply, and I was wondering where to get it from. Thanks to a tip I found on the internet I now have a good solution. I connect the U3S to the 12 V switching Power Supply I also use for my other radio equipment. The 12 V is not delivered to the U3S directly though, but via a cheap USB smartphone car charger instead which converts the 12 V to a stable 5.1 V, even when the voltage of the Power Supply is varying. I can also connect the U3S this way to for instance a 12 V gel cell battery. I already had the car charger lying around, but otherwise they often can be found for very little money.
The results of the U3S are really impressive, especially on the 40m band. For both the 40 and 20m band I use a HyEndFed 10/20/40 wire antenna in sloping configuration. On 40m I'm heard all over Europe, and occasionally I reach into Ukraine, Russia, Canary Islands, and across the Atlantic to the US. And who knows where I will be heard next; it's all up to the ionosphere and propagation conditions.
The 20m band has been a little disappointing. I did reach into the US East Coast and states like Alabama and Georgia, and I'm also being heard for instance in the more distant parts of Europe, northern Russia and the Azores, but it's the amount of spots that is disappointing and most of the time is low in number. This has nothing to do with the U3S. It's all about propagation, which lately has been really terrible. Or maybe my expectations for this band were just too high. I also wonder if on the 20m band maybe the loss in the relatively long length of RG-58 coax cable between transmitter and antenna is starting to play a role. I wonder how much of the 180 mW in the end is being turned into Effective Radiated Power.
Reported frequency drift on 40m is mostly 0. Reported frequency drift on 20m is slightly more, mostly -1, sometimes -2. On every first transmitting cycle after the U3S hasn't been used for a while, both on 40 and 20m, the drift is often bigger and up to -4, but this is mostly back to normal levels at the second transmitting cycle. I haven't experimented yet with setting a "park mode frequency", or with putting some insulation around the crystal of the frequency synthesizer to prevent any airflow changing the crystal temperature. This might bring the drift down to 0 on 20m as well.
Last but not least, I'd like to express my gratitude to Hans Summers, G0UPL of QRP Labs for developing and making available such excellent kits, and with very good after sales services and support to boot! A special e-mail forum offers support to U3S builders and users, and is a huge source of technical and operational expertise, coming both from Hans and other U3S users.
 |
| Front side. A red LED on the left of the front panel indicates if the transmitter is keyed (see also the photo at the top of this blog). I only had one push button, so the switch on the left toggles the button on the right between switch S1 and switch S2. |
 |
| The U3S transmitter module. On the left with the three yellow toroids is the plug-in LPF. |
 |
| Three switches on the rear side. One for switching on/off the unit, one for switching on/off the LCD screen, and one for switching on/off the GPS module. |
 |
| The GPS module with the patch antenna |
 | |||
| Rear side |
 |
| The case housing both GPS and U3S transmitter. A small window allows checking of the GPS module LEDs. |
 |
| The magical little box. Size comparison with a match box. |
