DTS: "Phase distortion? That would show up as what?" Did you place a Distortion Meter on the detected output to determine how much distortion was present? That is how it is normally done in the broadcast industry. DTS:"The new REA mod monitor sounds the same, so I assume NO phase distortion." Looking at the circuitry of the REA detector, it samples the RF signal directly via a dropping resistor before the diode detector from the transmitter via an external "T" connector, and then goes on to the interface unit. DTS: "As far as % of modulation, I set it using a scope, the mod monitor matched the scope, changing bands did not change anything." That is one way to calibrate a Mod Monitor but not the most accurate.