Connecting the DX Engineering Receive Preamplifier RPA-1 for optimizing weak signal reception on your main (transmitting) antenna is very easy. The RPA-1 is superior in specifications and performance to other outboard HF preamps and most that are built into transceivers. In some cases, enhanced weak signal receive can be achieved by using a combination of the transceiver's attenuator AND the RPA-1.
Connect the RPA-1 RCA phono jacks to any transceiver that has "RX OUT" and "RX IN" RCA phono jacks, using two high quality RCA patch cords. Make or purchase two mono RCA patch cables such as those intended for Video or Digital Audio. These cables will not attenuate RF signals because they are made with 75 ohm coaxial cable like RG-59 or RG-6, not cheap shielded audio cable.
For example, in the FT-920 manual, page 33 in the section (15) RX Ant Jacks, it reads, "....a receive preamplifier’s Input jack may be connected to the(transceiver) OUT jack, and the preamp’s Output jack may be connected to the (transceiver) IN jack......")
Using this connection method allows you to select RPA-1 preamplification of the main antenna with the transceiver front panel button "RX ANT", as on the FT-920. Push "RX ANT" again when you want to hear the main antenna without the RPA-1.
Learn more from the RPA-1 manual. The upated pdf link can be found on this RPA-1 page.