Topband: Separate RX antennas & protective relays

[Rolf Salme]

Hello all,

I am about to modify my TS-850 to accomodate a separate receiving antenna, and I have seen a number of suggestions how to do this, including Tree's. My plan is to cut the cable to the RX board in the TS-850 and put some additional circuitry in an outboard box, including a protective relay.

A. Assuming an SPDT relay in the box, kindly enlighten me regarding common sense, which probably applies to any setup of this kind; should I:

a. have the relay ground the line to the RX board and let the separate RX antenna float, or
b. have the relay ground the separate RX antenna (in reality the line from its preamp) 
    and let the line to the RX board float? 
c. or....?

B. I will also add  two protective 1N4148's somewhere in the line to the RX board; I have chosen this type, since they have an internal capacitance of only 4 pF, resulting in just an additional 8 pF across the receiver input. Will this extra capacitance affect receiver performance on higher bands such as 21 and 28 MHz, or would you recommend me to include these diodes in what is switched out when I bypass the box circuitry for the separate receiving antenna, i.e. returning my rig back to "normal" operation? 

73 & TIA,
Rolf
SM5MX