EQUIPMENT

The WSPR transmitter (beacon) covers the bands of 80, 40, 30, 20, 17, 15, 12 and 10m. The output power is about 200mW. It is powered via a 5 V USB port with a maximum absorption of 250 mA. It has an integrated GPS module for clock synchronization.

The transmitter is totally autonomous; Arduino firmware encodes WSPR packets and transmits them using a Silicon Labs PLL Si5351. The output from the PLL is a square wave that is amplified by a 74AC244 CI Line driver and adapted to a 50 ohm load via a MiniCircuits broadband transformer. 

The reference clock for the PLL is an Abracon ASTX-H11 TCXO 25 MHz oscillator. The reference has a stability specification of 2.5ppm which ensures good frequency stability when transmitting narrowband WSPR packets.

The signal comes out of the power amplifier as a square wave and must be filtered to remove harmonics. This is done by four switched low pass filters and an extra VHF suppression low pass filter. This reduces the harmonics by 50dB or more relative to the carrier.

More information on the hardware can be found on the website: https://www.zachtek.com/1012.