TX to RX: If switched from TX to RX (PTT goes low, Ch 1) first relay A drops off, contacts a1 and a2 are opened, removing the PA-voltage (Ch 4). Relay B is not powered any more thru contact a2 and falls off. The antenna relais was still powered thru b1 and switches off after settling time of relay B (Ch 2), the TX path is switched over to RX finally (Ch 3), about 7.5 ms after power was removed from the amplifier.
This circuit is used at DF2CK since May 2003 without any problems. Delay times may vary depending on what kind of relays are used.