Fred,
Good comments from both Bob-WB4SON and Jim-KQ6EA.
I might add that starting simple is a good approach as you will learn the effect that each improvement makes as you go. But saying that, if you can afford simple preamps like the ARR P144VDG and P432VDG ($79/ea.) and add a coax TR relay ahead of them it will work as well as more expensive switched preamps (depending on cost of relays). If you are only running up to 50w relays can be cheap (check e-bay, Fair Radio, Nebraska Surplus Sales). I would not trust a diplexer to have sufficient isolation to protect preamps.
I am re-installing my satellite antenna system and using this type of system for modes UV & VU. I have an equipment box for the preamps and switches mounted just below the Yaesu B5400 az-el rotator so only antenna cables run to antennas; I do have separate Rx and Tx coax lines to my equipment (which require modification to break out the Rx separate from Tx connector).
Using a switched preamp avoids the extra coax lines and mods so probably easier to implement with most radios. I have one mounted on another 2m antenna where I run 150w, but run a separate dc keying line and do not utilized the internal RF switching detector. This avoids hot switching the preamp. I am involved in eme so have a station sequencer to control TR switching in my station. This considered a "frill" for most satellite stations.
I decided to go simple with a M2 2M7 linear antenna and using part of my original M2 436CP42 (RHCP only - not switched). I'm installing 26 elements of that antenna. If I later feel need for CP on 144 then I may add 7 elements to the 2M7 and add RHCP phasing cable (again no switch). I have not found need for filters using high gain yagis for desense. Radio is old but good FT-736R running 30w barefoot.
I have equipment for 1268 and 2401 MHz but not installed for the present (used for AO-10/AO-40). I have an 8-dBic patch antenna for 2400 mounted but not connected. I have old preamp and drake converters for that band (stored).
73, Ed - KL7UW http://www.kl7uw.com "Kits made by KL7UW" Dubus Mag business: [email protected]