I would be glad to exchange ideas with readers. Email me so we can discuss about it. I have some bare PCBs to send to interested builders / testers.

RF Amplifier's 

Input Power Over-Drive Switch


   50 Ohms in/out SMA ports

​   Series and Shunt PIN- Diode Switch

   1 MHZ - 3 GHZ

   100 Watts max

    Compact 53 x 47 mm size

   Currently only a bare PCB is available

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I have received some emails from friends asking if we have anything available for protecting expensive RF Power LDMOS transistors because they can easiy be destroyed with excessive input power.


Here is a wideband solution  (LF to >3 GHZ) which uses an inexpensive PIN-diode RF Switch. Actually, there are two PIN diodes, one shunt-connected accros the output (which connects to the input of a Power Amplifier) and one connected in series with an external 50 Ohm load resistor. A wideband log-amp, the Analog Devices ADL5513, monitors the input power continuously. Its output voltage, if below a threshold, allows for the input signal to be applied to the output connector directly without any loss except this caused by the PCB trace. Both PIN diodes are not biased and there is no loss of power going to the output connector. But if above a threshold, a voltage comparator drives the MOSFET driver IC so to apply bias to the shunt PIN diode in order to place a short at the input of the expensive amplifier. At the same time, another PIN diode connects a terminating 50 Ohm resistor to the input signal. This lasts as long as the input signal is above the threshold.  This arrangement provides a wideband isolation of approx. 30 dB between the input and output ports. When the input power gets below the threshold it is driven to the output port again.