I weighed the pros and cons of tapping the low-level TX and RX lines inside of my FT-840 (the TS-930 brings these to the rear panel) versus installing an attenuator in the TX line. I opted for the attenuator instead of doing surgery on the radio.
The circuit is not particularly remarkable: the transceiver RF jack goes to a relay T/R switch. The TX side of the relay goes through a hefty 20-dB attenuator to a BNC jack. The attenuator is rated at 5 watts continuous duty and considerably more at lower duty cycles, perfect for this application. The RX side goes straight through to a second BNC jack. The TX circuit is normally closed (and RX normally open). This minimizes the chance of accidentally dumping 5 watts into the RX side of the transverter.
