Return Loss Bridge

A return loss bridge (or RLB) is a handy tool for determining various antenna characteristics including impedance and standing wave ratio (SWR).   In short, coupled with an RF signal source and power meter, it can make a good antenna analyzer.  The basic circuit is quite simple as shown below:

I opted for a prefabricated PCB from E&M Solutions to keep things neat and orderly. Three 49.9 Ω, 1% SMD resistors and an FT37-43 bifilar wound toroid (14 turns) completed the project.

Populated PCB

The fancy metal enclosure with laminated face plate took the most work and time but the end result is quite nice I believe.

Before putting the completed unit into service I need to characterize its performance.  As soon as my RF power meter is completed this will take place...soon hopefully 😏

Update (Fall 2018)
Power meter is complete so its time to finally check the RLB unit for proper operation.  Using my scalar network analyzer (Scalar Network Analyzer), I injected a 10MHz sine wave into the GEN port and measured the output with my power meter (RF Power Meter) at the DET port for a reference point.  Next, I inserted a 50 Ω dummy load at the LOAD port and remeasured.  The new reading was ~39dBm of directivity or return loss which is an excellent number (the larger the number the better).  This corresponds to an SWR of 1.023:1 (a perfect match would be 1:1) so this device is now ready for use.