a constant output having the same value as was previously provided as a constant output by block 105 thus as can be ascertained from fig1 there is a reference input which is used as applied to a non inverting input to cancel out the constant value provided by either of block 105 or 107 when they are in an inactive mode thus the summing amplifier 109 acts to provide an output which merely has to range from 1 2 volts to 7 7 volts while representing a change in received level input signal from 12 dbm to 77 dbm the recorded signal levels adjacent the various points in the block diagram of fig1 are applicable to one fm embodiment of the invention and the relative values may be typical of other fm embodiments as well as digital embodiments in summary then the invention in a preferred embodiment detects the level of a received signal which is operated upon by a circuit such as shown in fig2 which provides agc control after the signal exceeds a set amount such as 42 dbm by amplifying a signal representative of the output for values less than 42 dbm and for sampling the agc signal for values greater.