AD8307Power by ptamike

This sketch is missing a short description

**Introduction** This is a simple project for an in-line RF power meter covering 20Hz to 500MHz and 1nW to 100 watts. The prototype design uses a Arduino Uno board but is easily adapted for any Arduino board. The design also uses a 4 line 20 character LCD with an Adafruit LCD backpack. As a result, the project uses the Adafruit fork of the LiquidCrystal library and employs I2C communications. You can also use a conventional, multi-wire interface to the LCD by updating the appropriate line in the code. **RF Sampling and Measurement** The RF side of the project uses a 40dB resistive tap to provide a low level sample to the AD8307 module. The AD8307 module is produced by SV1AFN in Greece and is available via eBay. The resistive tap and AD8307 must be housed in separate screened enclosures (die-cast boxes are ideal). This is necessary to ensure stray RF voltages are kept well away from the AD8307's sensitive input stages. To provide the best resolution for the AD8307 output, the Uno ADC is set to use an external 2.5V reference. In the prototype a high accuracy shunt reference was used. **Calibration** The AD8307 is a remarkably accurate chip but performance can be optimised by trimming two of the variables. The slope of the log amplifiers can be measured by changing the input level by 20dB with a known accurate attenuator and measuring the change in the AD8307 output voltage. The voltage change should be 25mV per dB or 0.5V for a 20dB change. To calculate the slope value divide the attenuator value (20dB) by the voltage change. The other variable worth trimming is the intercept point which is the theoretical level (dBm) at which the main log amplifier slope voltage would reach 0V. This can only be measured and trimmed with the aid of an accurate power source.