[amsat-bb] Diplexer question

I'm installing a diplexer on my downlink side. Since I'm running two antennas, do I just leave the 145 MHz alone or is it more better to terminate it with a 50 ohm load I suspect the load is a better answer.

Does the preamp go prior to the diplexer? Or after?

Thanks and 73 de Tim, K4SHF FM04