I have assembled a 30 metre low-pass filter from Language Spy (link here) and soldered header pins to the GPIO on the Raspberry Pi zero.
Note that the Pi-LPF kit uses surface-mount components and provides a 7-pole Chebyshev low-pass filter for harmonic suppression.
WsprryPi was loaded onto the micro sd card. The RF output is 10mW, time will tell how far I will get. 30 metres was very busy at the time of testing with a contest . Tested over the weekend, it ran for 8 hours on a quarter-charged 10,000 mAh battery .
From the WsprrPi application notes:-
“….As the Raspberry Pi does not attenuate ripple and noise components from the 5V USB power supply, it is RECOMMENDED to use a regulated supply that has sufficient ripple suppression. Supply ripple might be seen as mixing products centered around the transmit carrier typically at 100/120Hz.”
I am using M0CVO’s HW-42HP Off Centre Fed Dipole antenna in the loft, link here .
Update 15th October 2016 – 20m filter board
The 20m filter board has been built. Shown below mounted on the Raspberry Pi Zero. Note that the USB cable connects the Wi-Fi dongle.