I am building the T/R switching circuit for an HF linear amplifier covering 80m band to 20m band. The current circuit takes a potential-free contact from the exciter and use this contact to turn on/off the relay. When PTT is pushed relay contacts connect the RF output from exciter to HF linear amp input and output of HF linear amp to antenna. When PTT is disengaged the linear amplifier is bypassed to connect the antenna directly to the exciter.
I like to avoid the PTT connection from the exciter to HF linear amp, by sensing HF carrier from exciter output and using this input to switch the relay. Problem with this approach is that when using SSB modulation, relay opens briefly as carrier is absent when audio is briefly at a low level. How to get around this problem?