The 6970 Power Meter comprises a plastic case moulded in two sections. The electronic circuits are located on two multi-layer PCBs using surface mounted components. The upper case section has the LCD PCB secured inside with the LCD visible through an aperture. The keypad assembly uses metal dome spring keys in a layered construction which is adhesively fixed to the case upper surface. Three NiCd rechargeable batteries are held in clips on the PCB. The lower case section has the Main PCB secured inside. The SENSOR INPUT multi-pin connector, fitted to the aluminium/polycarbonate front panel, is located in a groove at the top end of the case assembly. The DC input connector is similarly located at the bottom end of the case, with a voltage regulator heat sink plate attached to it. The Power Reference PCB is secured inside the upper section of the case, and is fixed to the LCD PCB. The power reference output N-type connector is located on the front panel of the case, next to the previously mentioned SENSOR INPUT connector. SYSTEM DESCRIPTION The heart of the 6970 Power Meter is an 8-bit microcontroller which provides control and timing for the unit and processes measurement data acquired through an analogue/digital converter (ADC), it also drives the liquid crystal display (LCD) and interfaces which the keypad. Program code is contained in internal ROM. The 6970 uses a signal chopper to provide a pulsed DC voltage which is proportional to the incident RF power and thus allows AC coupled differential amplification. The tuned input amplifier is distributed between the selected sensor and the 6970 input amplifier, as shown in Fig. 1-1. The second stage amplifier scales the signal as appropriate over four ranges before feeding the ADC, which converts the analogue signal to digital form suitable for the microcontroller to process and apply corrections. A digital/analogue converter (DAC) is used as part of the sensor zero operation to minimize and account for system offsets when no RF signal is applied. The internal power source comprises three rechargeable NiCd cells; two DC-DC converters are used to boost the NiCd power source to regulated +5 V and -5 V power rails required by the analogue and digital circuitry. The optional power reference provides a 0 dBm (lmW) 50 MHz signal from a level controlled oscillator based on a dual gate FET. Thermal compensation techniques are used in the design of the oscillator such that long term drift of output power due to temperature variations are minimised.