RF Limiters Part 2

Continuing on from RF Limiters Part 1, was not able to sort through the higher-power modular RF amplifiers box, but was able to run a quick test with a Yaesu VX-8DR walkie-talkie transmitter as a signal source at 446.000 MHz. Equipment used for this test was:

• Yaesu VX-8DR with freshly charged battery
• Place-holder for one of the AEL MW16301 RF limiters
• Midwest Microwave 2682 SMA-Male to N-Female RF adapter
• Narda 776-30 Medium Power Attenuator DC-4 GHz, 30 dB, 20 Watts
• N-Male to SMA-Female RF adapter
• MA/COM 2082-6173-10 SMA Attenuator DC-4 GHz, 10 dB, 2 Watts
• DIY Standalone RF Power Meter

Below is a photo of the setup for measurement verification (without a limiter in the line up). 

With the 40 dB of attenuation in place between the Yaesu and the RF Power Meter (PM), I measured the four RF power levels at 446 MHz, to confirm that the RF power meter was not saturated or operating in a non-linear fashion. The data captured was:

The radio was put back in the charger to top off the battery while setting up for the next test (insertion of the AEL RF limiter into the chain at the radio's output). Due to the stresses placed on the Yaesu's transmitter when the limiter is in place (and limiting), I chose to only test with the limiter at the L2 (1 Watt) RF transmit level.

Below is the test setup with the AEL limiter in place at the Yeasu's antenna port.

Based on the similar AEL MW16301 RF limiter data sheet (a different serial number), I should expect to see around +16 dBm pass through power at 500 MHz with a +30 dBm (1 Watt) input signal. I'm testing at 446 MHz with a 1 Watt input signal, so am expecting +16 dBm also. Below is the measured leakage power received at the stand alone RF Power Meter (without the 40 dB correction applied).

Here are the test results from operating the transmitter through the RF limiter. The second column is the measured power meter reading, the third column adds back in the 40 dB of attenuation in the path to display leakage power in dBm, and the last column is the leakage power in watts.

The AEL limiter is reducing the transmitted through power from +30.2 dBm down to +14.6 dBm (a difference of 15.6 dB). Transmitted power level went from 1.0 Watts down to 29 milli-watts. The RF limiter works!

Plan to set up this test again and test the remaining three RF limiters in a similar fashion. Hoping to also get some time to see if I have a 1 Watt capable RF amplifier in the lab stock. If so, I can test limiters up at 902 MHz to see how they'll behave with the future 902 MHz transceiver. (Can also use that amplifier at the Pluto's TX output to run the entire RF transmit chain at realistic power levels. Looking forward to this test!)

More fun ahead (now with higher RF power)!

All author photos captured with an iPhone 16e.