The Si5351A is a clock-generator chip manufactured by SiLabs that I have bought from QRP-Labs. From manufacturer specifications it can produce three simultaneous independent squarewave outputs (50 ohm impedance) between 8 kHz and 200 MHz. Hans Summers from QRP-Labs tested the real frequency range of the Si5351A outputs. He found that the minimum frequency configuration with 27 MHz crystal produces 3.515 kHz output. The maximum frequency appears to be an internal limitation (not limited by the configuration) and was approximately 292 MHz. Of course, as Hans says, outside the specified range of the datasheet (8 kHz – 200 MHz), there are no guarantees.

The chip configuration is possible via a microcontroller with I2C interface (two-wires).

This kit I have soldered today is a “breakout board” contains pre-soldered Si5351A chip, 3.3 Volt regulator and I2C level converters.

Let me explain you that a so called “breakout board” is a board that “breaks out” its pins onto a printed circuit board that has its own pins that are spaced perfectly for a solderless breadboard, giving you easy access to use the integrated circuit. There are all type of breakout boards – but most of them are for different types of sensors, for example: accelerometers, ultrasonic distance sensors, RFID tag sensors, temperature sensors, pressure sensors, and they even have sismic breakout boards for sensing dinosaurs’ footsteps!

So, the Si5351A synthesiser module kit runs from a 5V or 3.3V power supply. The tiny 0.5mm pin-spaced Si5351A chip is pre-soldered to the PCB at the factory. The PCB size is 1.3 x 1 inches (33 x 25 mm). The remaining components are all through-hole components so construction is easy. The circuit contains a 3.3V regulator and I2C level converters, for use with 5V microcontroller systems. The kit may also be built without the level converters or regulator, for use in 3.3V systems. The kit has a 2 x 10-pin 0.1-inch header for all connections. Additionally pads are provided on the PCB for soldering SMA connectors if you wish. The kit uses a 27 MHz crystal as the reference oscillator.

The synthesizer may be used in a variety of projects. The pinout has been designed to be somewhat similar to the popular AD9850 DDS module and may be substituted in certain cases (with appropriate software changes in the controller). This Si5351A module is also designed to be compatible with the Ultimate3/3S QRSS/WSPR kits. It can be plugged into the U3 kit with certain minimal hardware modifications to the U3. It is directly compatible with the Ultimate3S kit without modifications. It requires Ultimate3 firmware v3.07 or above, to communicate with the Si5351A via I2C. Note that for use in the original U3, not U3S, (PCB revisions 1 to 4), pin 12 of the header needs to be removed before installation.

Roberto Pietrafesa (IZ7VHF)

Monteiasi, Italy, February 25 2017.