This is usefull when using a big PA and or for RF bandpass filters. My FT102 + transverter recently broke down So i now use the IC706. The sensitivity of the IC706 is not what I was used with the transverter. There is raise of noise when connecting the antenna so in fact it is just sufficiënt.
Using the IC706 with an external PA you might need a lownoise preamp. But it is not so easy to use because without extra protection relays it can, and sure will be destroyed by the driving power of the IC706.
The best solution is having an extra RX–only input like most bigger tranceivers have. This way the preamp can be placed direct behind the first antenna relay and the output of it Goes to the RX-only port. The best place for this antenne relay of course is as close as possible to the antenne to avoid extra cable loss however not so practical.
Adding a separate RX port is an easy and clean modification. There is a spare opening in the backpannel where an extra BNC connector can be placed. Extra rings are used to fit because the hole is to big for the BNC. Then this BNC must be connected to J1 (rx) point found at the back of the filterunit.
The filterunit is situated top-backside. After removing 5 screws the board can be moved up at the backside Just enough to mount the BNC underneath it. It is not needed to remove it completely that would be a problem because of all connections to it.