Optional RX Input
Note from Steve, November 4th 2019: There is no switching or software control of the optional RX input. If you look at the HL2 schematic on the "RF Frontend" page, you can see that it is just a parallel input from the TR switch. The main purpose is for more controlled feedback of TX signal to the RX during TX for Pure Signal. You could also use it as an always connected RX input to a different antenna. You can solder coax directly to RF3 on the HL2 and then run the connector to the back panel. There are also a uFL footprint RF4 and RF5 for a removable connection. See https://www.adafruit.com/product/1661. These provides direct connection to the ADC pre and post LPF. You can run a cable to one of these and remove B81 to disconnect the RX from the TR switch. You either have to disconnect the RX from the TR switch, keep the TR switch always in TX, or remove the TR switch if you want full duplex with the optional RX inputs.