The quality of the devices and the design of the amp is significant. In the cellular world at 850 I have seen cheap poorly designed (talking thousands for these units) TTA's generate more crud from minimial colocated signals then the well designed cheap ones. All the units I now use have a high IP3 point with integrated filters or duplexers. The unit ADC Telecom used to make had the filter integrated in the housing (machined out of a solid aluminum block). I was able to use these in downtown settings without fear of intermod. Newer units work as well but now have a seperate filter from the housing. Moral of the story: It's design not price that is the key. Cheaper not always badder. Compare specs. Other suggestion would be to establish the power level where the interference begins. Though it is not linear it will give u a sense of the degree of interaction between the UL and DL antennas. Intermod and desense always has a bit of magic to it thanks to its none linear behaivor
Hope this helps someone Dave D WB7DRU
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Another option is to use a preamp with good filtering on the input. I had issues with Mode J desense with my Icom AG-35 preamp, but have none now that I have switched to SSB Electronics preamps.
As always, Your Mileage May Vary (YMMV).
73, Drew KO4MA
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