I purchased a used Sinclair Q3220E duplexer on eBay for $700 and took it to a reputable radio shop today to have it tuned. The radio tech said it tuned fine with no problems, however, after I got home I looked over the piece of paper the tech gave me that had the isolation and insertion loss values written on it, and I was surprised to say the least that the insertion loss is 1.8db on lowside and 2.1db on the highside. This db loss is way out of specification which is 0.8db for this duplexer model with many sources citing tuning can get it down to 0.6db loss. The tech put the duplexer after a 50 watt repeater and said he recorded 38 watts after the duplexer.
Does anyone have experience tuning this specific model duplexer who can offer insight on why the high insertion loss?