Back in the days when we operated Vampires, Sea Venoms etc era aircraft I was issued a brand new Kiowa with the very latest digital tuning radios and we had great comms problems initially, checking by the techs found them to be spot on freq, no faults, then found if we tuned a step up or down we found a freq that worked, the stations we were trying to communicate with were old tech and their freq standard were rather more lax.