The core is the Hermes SDR board with a 16 bit A/D converter. It is full duplex capable and is therefore able to use predistortion. The Hermes board needs an external RX/TX switch and in my case a small driver PA with 5W. My HVF-1k2 power amplifier needs about 1W - 1,5W input power on the higher bands and the Hermes board unfortunately delivers only 500mW. You should not do without a decoupling between SDR board and TRX input.
In the picture you can see two attenuators, one between the Hermes TX Out and the PA Input. This serves on the one hand to not accidentally overdrive the small PA and on the other hand for decoupling.
The second attenuator has 30dB attenuation and is used to attenuate the signal present after the 30dB coupler again, so as not to destroy the second input of the Hermes.
Inside view HF deck prototype