Make a great WSPR beacon from a QRP-Labs kit - Ultimate3s

Using WSJTX to test your antenna system is easy, we've documented how to do this on this page: WSPRX. But...maybe your don't want to tie up your transmitter and PC, you just want to plug in a box, switch on and let the rest happen automatically. 

QRP Labs sells the Ultimate3s beacon kit to do just this.

Building the Ultimate3s

This kit can be a little tricky to build, but it is doable and fun. This kit took me over four months to get this working from placing the order to making a proper contact.Why? Well I made some mistakes during the build, but also learned some things in the process. So on this page I'm going to share what I have learned about this kit in the hope that it helps others.

The instructions that come with the kit are excellent and need no further explanation. However, there are some tips and advice which may help avoid potential pitfalls and improve your enjoyment of this great kit.

Building tips for the UltimateS3

Assembly mistakes to avoid

Here is a list of the mistakes I made whilst building this kit:

  • Applied too much power and blew up the micro controller and GPS board
  • Connected the U3S main connector 180 degrees the wrong way round, blew up the micro controller
  • Didn't fit a LPF to location #1 of the relay board, so no Tx output
  • Missed some of the links on the relay board
  • Did't set the frequency as it says to do it in the manual (1.4kH higher than WSPR frequency)

Tip: Don't make these mistakes

Assembly essentials

I highly recommend this build approach:

  • Get the single band 40m U3S working, before fitting the relay board
  • If you get no spots then it's not working
  • Check each LPF in the single band U3S configuration before moving on to the relay board
Ultimate U3S build WSPR beacon kit
Ultimate U3S build WSPR beacon kit

5 Volt supply for your U3s

The U3S requires a 5V supply, exceeding this will blow up the GPS board and processor. There is no forgiveness, so be very careful!

I used a variable PSU module purchased from an online auction site to step down my 12V supply down to a smooth 5v: 

  • LM2596 DC-DC Switch Adjustable Buck Regulator Converter 3V-40V

This device regulates the voltage regardless of the input voltage, so it will protect your U3S. It will also provide a nice stable supply.

Glue your torroids down using hot-melt glue!

The the Low Pass Filter filter boards are tricky to make and they're easily damaged during handling. To avoid damage I used hot melt glue to secure them in place after testing.

Use pins, sockets alignment marks and labels

I found that it was much easier to use header pins and sockets to make this kit, soldering wires to the board will cause issues during testing and modification in the future. Boxes of header pins and sockets are available form Amazon and are extremely handy to have around the shack.

It's easy to connect things the wrong way round, or plug things in the wrong slot:

  • Label plugs and sockets. Mark LPF's
  • Mark conector orientation with paint (i.e blob of red paint on one side of a connector)
  • Make connection to a good standard, pull test connections to ensure they are robust

Protect the Si5351A from heat to reduce drift

The enemy of those WSPR spots is drift. As soon as your Q3S starts to transmit, it will heat up the crystal and you will get drift, this could stop you from logging any WSPR spots. So this is important.

There are two ways around this:

  • Buy the OCXO/Si5351A 
  • Protect your Si5351A from heat.

Protecting your Si5351A from heat is well documented on the QRP Labs website, but it not obvious and can be missed. This is what I did:

Add a heat sink

To protect your Si5351A from heat you have glue a lump of metal to the crystal to slow and absorb any temperature variations.

Add a heat box

I also built a box around mine using thick plastic card to make a small box. This worked very well.

Either way, solving heat related drift is going to be required for those WSPR modes, so you'll need to address this right away and should consider this during your build.

...more on drift

Use Park mode to knock that drift out.

  • I set mine to: 1
  • Frequency set to: 000,00 1,400Hz

All of the above were required before I could get those WSPR spots.

Ultimate U3S build Si5351A heat sink
Ultimate U3S build Si5351A heat sink
Ultimate U3S build Si5351A heat box
Ultimate U3S build Si5351A heat box

Fit the programming pins during your build

If you fit the programming pins during initial assembly, you'll be able to flash your own micro controller very quickly and at minimal cost. Fitting the pins during the build could make life a little easier later on.

Tip: I've included instructions on how to flash the AT328P below.

Flash you own ATMega 328P

I did damage a couple of the micro controllers when setting up the U3S. It is far easier and cheaper to flash you own replacements. 

What you'll need

The following hardware is required to flash your own Ultimate3S micro controllers:

  • AVR USBASP programming lead (with six pin connector)
  • A pack of ATMega 328P's
  • A copy of the latest firmware - from the QRP-Labs website

Install the AVR programming software and driver

Digital SWR meter PCB build
Populating the SWR meter PCB

Install the AVR programming lead driver

1) Install the usbasp driver for the AVR programming lead:

2) Select the USBASP device, then install the lbsub driver

Install  AVR dude

1) Install AVRdude:

2) Here is the manual: 


Flash the U3S micro controller chip

Flash a new ATMEGA328p

  1. Fit the new chip to your Ultimate3S
  2. Copy the new firmware file in your c:\users\[your name]
  3. Apply power to your Ultimate3S, plug in your programming lead
  4. Open the cmd window:
  5. Write this line in the command editor and hit enter:

avrdude -B10 -c usbasp -p m328p -U flash:w:v3.12a.hex

avrdude -B10 -c usbasp -p m328p -U lfuse:w:0xF7:m

avrdude -B10 -c usbasp -p m328p -U hfuse:w:0xDF:m

avrdude -B10 -c usbasp -p m328p -U efuse:w:0x04:m


You should see the script run and program the Atmega328p chip

 If you see an error, the check your settings and try again!

Fit a smaller GPS module

My original  QRP-Labs GPS module never really worked, but I wanted the automatic clock functions to make using the U3S easier. I didn't want to wait a further three weeks for a replacement kit so I started searching the internet and I soon found a suitable GPS module available from a well know on-line store for $10 USD (included next day delivery!). 

  • MakerHawk GPS Module 51 Micro controller GPS Compatible NEO-6M STM32 Arduino Navigation Satellite Positioning GT-U7

The replacement GPS module is  smaller and works just fine. Not only does this GPS option leave much more room in the case for the receiver kit, it's also easier to mount the antenna to the top of the box.  

Setting up the GPS board

Now, you may not need to change any settings and your GPS may work as soon as it is plugged in. However, I needed to activate the time message, to do this I had to install the GT-U7 GPS software that is available for free (U-Center). I connected to the GPS board to my PC using a regular USB lead and configured the following items (very easy to do):

  • INF: Protocol=1-NMEA
  • MSG:F1-04 PUBX04
  • NMEA=CNF-NMEA-DATA1, Version =2.3
  • TMODE:1- Survey in
  • TMODE 2: 2-Fixed Mode , Use Lat/Lon/Alt
  • TMODE 3: 0-Disabled
  • TP: Duty cycle=10%
  • TP2: 1- TIMEPULSE2, Active, Frequency 1 Hz, Length=100000us

Tip: I also purchased a bigger GPS antenna which multiplied the satellite locks by 3! 

Setting up the U3s for WSPR