Simple QRO sequencer for Xiegu G90

I saw some XPA-125 destroyed and I heard about few Xiegu radios with PA burned due to "hot switching". The correct way to switch the radio+QRO is to have the QRO keyed first then the RF to be sent to it. The best delay is around 50msec when relays are used in QRO and around 15-20 msec when the switching is made with PIN diodes. Therefore, a "sequencer" circuit has to be used. This is placed between the microphone and the radio and have output for QRO. If some other devices are present in the RF path (like antenna switches or RF preamplifiers), the Rx/Tx sequence has to be carefully determined and implemented with a more complicated circuit. But for te simple goal of delaying the presence of RF at the QRO input, a simple circuit can be used. The delay with R3C1 is around 120 msec and can be reduced by using a smaller capacitor at C1 for CW.

While there are many other methods, including microcontroller driven variable delays, this circuit is a simple one with components which may be already in the junk box.

This ideea came from a discussion with Mel, K6KBE.