100W T/R Switch with VSWR Bridge

100W T/R Switch and VSWR Bridge

This circuit is designed to switch a power amplifier (up to 100W) into the TX path during TX. It also has 0-5V outputs proportional to the forward and reflected power through the circuit for metering and amplifier protection. Designed for microprocessor or discrete control interface.

Here is the block diagram:

The switching is compatible with 3.3V or 5V logic and the forward and reflected voltage outputs 5V = 100W (non-linear). 

The PCB is 5 X 5 cm (2 X 2 in) and is designed to stack with amplifier boards.

The frequency range is 1.8 - 54 MHz.

Connector Pinout:

Pin 1: Ground

Pin 2: V rfl

Pin 3: V fwd

Pin 4: High for TX, Low for RX, 2.5-15V High, 0-1V low pulled down with 100k.

Pin 5: N/C

Pin 6: 11-15V 13.8 nominal, 100mA max.

Schematic and BOM can be downloaded below.

Here are photos of the assembled board:

Assembly tips:

• 1.  T1 and T2 each have two windings. The 10 turn windings, made from #24, $26 or #28 enameled go in the hole with round pads. The one turn winding, made from #22 stranded wire go the holes with square pads. The core is a FT50A-61 or stack two FT50-61's on top of each other.

  2.  Install the SMT components before the thru-hole parts so they don't get in the way.

To convert the voltage from the directional coupler to Watts use the following equation:

P(watts) = 2 * (Vdet * 1.54 + 0.05) ^ 2

To convert the voltages from both detectors to VSWR use the following equation:

VSWR = (1 + Vref / Vfwd) / (1 - Vref / Vfwd)

Vfwd can't be 0