Antenna Analyser

An antenna analyser is just a simple bridge circuit. A signal source drives the bridge, and the sensing is made between the centre of the 2 x 50 ohm resistor side and a 50ohm resistor and antenna on the other side. This yields two signals, FORWARD and REVERSE.

VSWR = (FWD - REV)/(FWD + REV).

PWR = (FWD * 2) ^ 2 / 50

Using a clever IC, the MCP6002, which is a a rail-to-rail op-amp, amplifies the output from the bridge, so that low power from the VFO shield (see previous postings) can be used to drive it. The frequency is tuned by the Rotary Encoder connected to the VFO and the LCD, also connected to the VFO shield, displays the results.

CIRCUIT



A similar circuit, with RF input from your TX can make a very good resistor SWR/PWR meter. But in this case the gain and signals to the op-amps must be attenuated to keep the outputs below 5V for the Arduino A/D converters on A0 & A1.

Note:

1W = +30dBm = 7.1V

2W = +33dBm = 10V

10W = +40dBm = 22.5V