At RML, we have a whole stack of cheap AM radio receiver kits to practice assembly and learn more about electronics. As of October 2015, a young adult is building one.
Some software-defined radio receivers have also sparked quite a bit of interest from the maker/tinkerer community:
"rtl-sdr" is a generic term for cheap USB digital TV (DVB-T) receivers that use the Realtek RTL2832U chipset, which can function as general purpose software defined radios (receive only). All rtl-sdr compatible devices employ the RTL2832U as an ADC and USB controller, but different RF tuners may be used. Note that rtl-sdrs do not transmit! Typical specs (some depend on specific tuner):
Device Cost: ~£5-20 (Look on eBay, Amazon, or AliExpress) Frequency range : 24 - >1760 MHz (100 KHz - 24 MHz in direct sampling mode) Max sample rate: 3.2 MS/s (2.6 MS/s in practice) Resolution: 8 bits/sample Noise figure: < 4.5 dB
The RSP (Radio Spectrum Processor) from SDRplay is a Software Defined Radio which can turn a PC into a general coverage receiver spanning Long Wave (100KHz) through to Microwaves (2GHz). The SDRplay is home-grown in the United Kingdom and offers a much wider set of capabilities than the RTLSDR.
Device Cost: £118.80 Frequency range: Total coverage from 0.1MHz to 2GHz ADC performance: 12 bit native ADC Max Sample Freq: 2MSPS – 10.66MSPS 10.4 ENOB 60dB SNR 67dB SFDR