Radios

There are a number of radio modules in use with descriptions :

Module	Price	Temp Stability	Complexity	Size/mass	Frequency	Modulation	Further Information
Radiometrix NTX2	Medium	Poor	Simple	Medium	434.075 or 434.650	FM (analogue)	Data Linking an Arduino to a Radiometrix NTX2 Transmitter End of life
Radiometrix NTX2B	Medium	Excellent	Simple	Medium	434.000 → 434.750	FM (analogue)	Data Linking an Arduino to a Radiometrix NTX2 Transmitter Breadboard friendly pitch
Radiometrix MTX2	Medium	Excellent	Moderate	Low	434.000 → 434.750	FM (analogue)	Data Linking an Arduino to a Radiometrix NTX2 Transmitter Effectively identical to the NTX2B
Radiometrix LMT2	High	Excellent	Simple	High	433.900 → 434.650	FM (analogue)	Data Superseded by MTX2
Radiometrix TX3H	?	Poor	Simple	High	869.50Mhz	FM (analogue)	Data
Radiometrix HX1	Medium	Good	Moderate	Medium	APRS 144.800/143.900/144.390	FM (analogue)	Data
HopeRF RFM22B	Low	Poor	Moderate	Low	413.000 → 453.000	FSK (PLL) + others	RFM22B Insulation is very important with this module, the crystal is only rated to -20'C. The module has exhibited instability and failure when exposed to low temperatures. It is recommended to reboot the module every 20 telemetry transmissions.
CC1101/CC430 (bare IC)	Low	Depends on crystal	Software:Moderate; Hardware:Moderate	Lowest	434 & 869 ISM	FSK (PLL) + others; FM (analogue) with external components	datasheet (cc1101), datasheet(cc430), single component match and filter CC430 comes with MSP430 processor for overall smallest area

Notes :
“Poor” stability means unless well insulated the frequency will drift noticeably.
“Simple” Complexity means suitable for beginners.
All modules support RTTY, analogue FM ones support APRS via external DAC