Radio frequency communication circuitry configured to couple in series with a two-wire process control loop, the radio frequency communication circuitry configured to enable wireless communication to be added to a new or existing process control loop or field device, the radio frequency communication circuitry configured to be powered by the process control loop and installed on the loop, the radio frequency communication circuitry characterised by comprising: a sense resistance and a power supply diode configured to couple in series with the process control loop, the power supply diode is part of a power supply circuitry which includes a first capacitor, an input filter, a voltage regulator, a second capacitor and a secondary filter, the secondary filter includes a third capacitor and a resistor, the power supply circuitry is configured to generate a power supply voltage (V DD) relative to a circuit ground for use by circuitry in measuring the loop current and wirelessly transmitting a resultant signal; the radio frequency communication circuitry comprising: an input circuitry which includes the sense resistance and is configured to measure an analogue current flowing through the loop; and a RF transmit/receive circuit coupled to an antenna which can be configured as an internal antenna, external antenna or combination thereof, wherein the radio frequency communication circuitry is configured to couple across the two-wire process control loop such that the loop can terminate at another field device, when coupled to a field device the radio frequency communication circuit is in series with the process control loop where it utilizes the current flowing through the loop to power itself, the radio frequency communication circuitry is configured for nominal operation at between 3 and 4 volts and the power supply diode, which is a zener diode, along with the sense resistance is configured to set this operating voltage, the zener diode acts as a shunt element in series with the loop to develop a preregulated voltage on the input filter, in operation the loop current which is not used by the radio frequency communication circuitry is shunted through the zener diode, the input filter is configured to isolate the loop from noise or load fluctuation generated by the radio frequency communication circuitry, the voltage regulator of the power supply circuitry is configured to supply the power supply voltage (V DD) to the radio frequency communication circuitry; and the secondary filter is configured to store energy and further decouple circuit loads from the regulator, in operation the radio frequency communication circuitry allows the output voltage of the secondary filter to sag by several hundred millivolts during circuit load changes. a sense resistance and a power supply diode configured to couple in series with the process control loop, the power supply diode is part of a power supply circuitry which includes a first capacitor, an input filter, a voltage regulator, a second capacitor and a secondary filter, the secondary filter includes a third capacitor and a resistor, the power supply circuitry is configured to generate a power supply voltage (V DD) relative to a circuit ground for use by circuitry in measuring the loop current and wirelessly transmitting a resultant signal; the radio frequency communication circuitry comprising: an input circuitry which includes the sense resistance and is configured to measure an analogue current flowing through the loop; and a RF transmit/receive circuit coupled to an antenna which can be configured as an internal antenna, external antenna or combination thereof, an input circuitry which includes the sense resistance and is configured to measure an analogue current flowing through the loop; and a RF transmit/receive circuit coupled to an antenna which can be configured as an internal antenna, external antenna or combination thereof, wherein the radio frequency communication circuitry is configured to couple across the two-wire process control loop such that the loop can terminate at another field device, when coupled to a field device the radio frequency communication circuit is in series with the process control loop where it utilizes the current flowing through the loop to power itself, the radio frequency communication circuitry is configured for nominal operation at between 3 and 4 volts and the power supply diode, which is a zener diode, along with the sense resistance is configured to set this operating voltage, the zener diode acts as a shunt element in series with the loop to develop a preregulated voltage on the input filter, in operation the loop current which is not used by the radio frequency communication circuitry is shunted through the zener diode, the input filter is configured to isolate the loop from noise or load fluctuation generated by the radio frequency communication circuitry, the voltage regulator of the power supply circuitry is configured to supply the power supply voltage (V DD) to the radio frequency communication circuitry; and the secondary filter is configured to store energy and further decouple circuit loads from the regulator, in operation the radio frequency communication circuitry allows the output voltage of the secondary filter to sag by several hundred millivolts during circuit load changes.