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.
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.
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| 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.
