RF Limiters Part 1
The envisioned 902 MHz transceiver based on an ADALM Pluto SDR with the KK7B filtered front-end, and a one or two stage 900 MHz band circulator will likely need a RF limiter at the receiver port of the circulator. This limiter protects the receive chain from the transmitter's signal if the antenna is damaged or disconnected (with the circulator routing all reflected/received power from the antenna out (Port 2) to the circulator termination/receiver (Port 3) connection.
A look through one of the small modular RF components cases yielded four limiters to consider. All use SMA connectors. Three are all the same part number (AEL MW16301) and the fourth is a Hewlett Packard 5086-7261 (possibly pulled from a HP spectrum analyzer). One of the AEL limiters included a final-test/measured test data sheet. A quick internet search for AEL MW16301 yielded zip/nada...
The internet shows multiple sellers of the HP 5086-7261 limiter, with all saying it covers DC to 2.5 GHz (as marked on the case) and that they are rated for 10 Watts (not marked on the case). Wondering what the leakage (pass through) level is for this unit?
Below is a photo of the limiters and the AEL test data sheet.
Reading data off of the AEL MW16301 data sheet:
- Limiters work from 2 to 1000 MHz and have less than 0.5 dB insertion loss and less than 1.3:1 VSWR over that range
- For +43 dBm input, leakage is 17.2 dBm at 100 MHz
- For +43 dBm input, leakage is 19 dBm at 800 MHz
- For +30 dBm input, leakage is 16 dBm at 500 MHz
- For +30 dBm input, leakage is 16 dBm at 1000 MHz
- Tests were performed on SN 1338 on 2/5/84
All of the limiters are in very good condition, with the AEL units appearing unused. All would benefit from being tested to confirm functionality before any are used in the 902 MHz transceiver.
Next step is to create a RF limiter test setup (likely focused on the 900 MHz band). Will have to check how much RF power I can easily generate with my ZHL-1042J lab RF amplifier (thinking it is about +24 dBm at 1 dB compression?). Might also just test with one of the Yaesu VX-8DR walkie-talkies. They have four power levels and provide easy testing at VHF and UHF frequencies (not 900 MHz though). Otherwise, I can check the high-power modular amplifiers box out in the garage to see if I can get over +30 dBm (1 Watt) at 900 MHz. There are some larger amps out there that might just do the trick. If not, the Yaesu radios will work in a pinch (down at 450 MHz).
More fun ahead (now with higher RF power)!
NEW: See RF Limiters Part 2 posting here.
All author photos captured with an iPhone 16e.