HackSpace Magazine free PDF

Issue 6 of HackSpace magazine mentions amateur radio and provides links to the RSGB and ARRL 

Pages 56-61 looks at radios from crystal sets to RTL SDR dongles. The article covers turning your Raspberry Pi into a radio transmitter and provides a design for a low pass filter to reduce the harmonics that can be generated.

They say "You may be happy to play with a simple regenerative receiver or a cheap RTL software-defined receiver but, if your interest goes further, the field of amateur radio is a logical next step."

Hackspace magazine issue 6 
https://hackspace.raspberrypi.org/issues/6

Direct link to free PDF download 
https://s3-eu-west-1.amazonaws.com/rpi-magazines/issues/full_pdfs/000/000/013/original/HS_6_Digital_Optimised_2.pdf