I thought I’d share this simple design for a coax relay sequencer circuit and hope someone finds it useful.
It’s not my design but I have used it in various projects over the years and it works really well.
The basic operation is two relays are energised upon PTT, one pulls in faster than the other (pot1 adjusts the delay time).

I used the contacts on the fast relay to safely switch a pair of coax relays on one of my homebrew amplifiers and the slow relay to delay application of the bias supply until the coax relay contacts have gone over.

The sequencer helps to prevent hot switching of the contacts, particularly on the output coax relay which may safely carry many hundreds of watts when sequenced correctly.

It can easily be built on some veroboard.

List of parts,

5 off 1N4007 diodes
2 off 12v DC SPDT miniature relays
1 off 500ohm PCB mount cermet potentiometer
2200uf Electrolytic capacitor (25v working voltage or higher)