The Yaesu DR-2X has no front end filtering to speak of and relies completely on the duplexer and other front end filtering to survive. I had one on a perfectly tuned 4 can Motorola 1500 series Bp/Br duplexer (85dB isolation) with 85w amp and it was not happy with noticeable desense. I replaced the duplexer with a Celwave PD526 series six cavity 120dB isolation and it finally plays nice. I also found my 5w input amp fed by the DR-2X at 5w had all kinds of spurious crap coming out of the DR-2X transmitter but the DR-2X was fairly clean at 20w so I use the repeater at 20w with a 6dB attenuator into the amp for 85w out and that is working ok.?
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If you have a certain amount of isolation in the duplexer, adding a preamp with no preselector filter will roughly reduce the amount of duplexer isolation by the amount of gain the preamp has by amplifying transmitter noise. Plus you may be hitting the preamp with enough out of band energy to create IMD which can raise the noise floor or produce ghost signals that may land on your repeater input frequency. I would suggest looking at the output of the existing amplified 8-way divider with a good spectrum analyzer to see what the repeater receiver is seeing when running at 100w. Is the desense due to increased noise floor or is there an actual signal present on the input only when the repeater is transmitting, etc? If so you can start removing things to see what affects the desense like remove the preamp and connect the repeater receiver right to the duplexer and see if the desense is reduced or eliminated. I see you have run the repeater at 20w without the power amp and desense is reduced but you need to know why its better.?
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I suspect the main problem is the duplexer does not have enough isolation and using a preamp without an adequate cavity filter in front of the preamp is degrading isolation and the power amp is adding to the problem. A better duplexer and an adequate preselector filter ahead of the preamp with amp running at 250w in the future might all work together but maybe not with a DR-2X but might with a commercial quality repeater.
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When you say the input goes away when it rains or snows are you talking about the receiver input as in it doesn't receive at all during rain or snow? If so to what extent? Just weak distant signals or from a radio transmitting right at the repeater site? How bout a service monitor right into the duplexer or repeater receiver? This sounds like a separate problem needing more info.?
