Both the KX2 and transverter have instant switching. In the transverter circuit the power is switched between the RX and TX sections and there’s a diode across the RX input that is biased on when the PTT is active.
It should be all lovely-jubbly. Wire the ACC key out from the KX2 to the transverter, KX2 ant to transverter input through an attenuator, transverter ant to the 2m ant. Then VOX on, a bit of delay (I just cannot cope with full QSK) tap the paddle and you should be in business. The KX2 should go into TX, the key out will go low, the transverter will switch into TX almost immediately then the KX2 will make some RF and Bob’s your Uncle. Let go of the paddle, the RF will stop, VOX delay will time out, the key out goes high, the transverter switches back to RX.
The transverter switches the supply to the TX and TX stages with its PTT input and it’s got diodes to protect its front end from its own PA output and there’s another diode to isolate its RX section output from the RF input. It should be happy.
We can assume Elecraft’s designers are capable of walking and chewing gum at the same time so they will have designed their KX2 so the key output goes low always before any RF is produced so whatever is on the key output should get switched over before the RF appears. That all seems fine and dandy.
My only worry is I’d like some kind of resistive 50ohm load between the KX2 and transverter in case the input impedance is something so revolting the KX2 doesn’t like it.
So I’d order their attenuator board and use that so that the system was “proof against activator being cold and damp on a summit and forgetting to set the KX2 output power”; you know you are going to do that at some point. Then you’ll have let all the magic white smoke out of some of the transverter transistors.!
Their board has relays for switching the attenuator pad out of circuit.
I’d stick mine in the post to you tomorrow so you could build up your system on Wednesday. Then you could order an attenuator at leisure and send it to me. But my board is hiding in the shack and I can’t find it. I can’t the Z-match or the bag of T-50/T68 toroids either.