What is the difference between the STD-502-R and STD-503, STD-504?

The main differences are communication data rate, channel step option, size/weight, antenna connector type and current consumption.

	Data Rate	Channel Step	Size Weight	Antenna connection	Consumption current / 3.3V
STD-502-R	9.6 kbps* 19.2 kbps	No	50 x 30 x 9 mm 24g	RP-SMA	55 mA (TX) 65 mA (RX)
STD-503	19.2 kbps	Yes	40 x 29 x 5.5 mm 10g	MHF	48 mA (TX) 55 mA (RX)
STD-504	19.2 kbps	Yes	40 x 29 x 5.5 mm 10g	MHF	55 mA (TX) 60 mA (RX)

* Not available in US and Canada.

The STD-503 includes on-board temperature sensor and the STD-502-R does not.