1 and has the door 5 for access thereto formed in said module 1 a push button s1 closes the switch and energizes a relay k2 closing contact a and supplying voltage from the battery b1 to the resistor 44 and diode d11 which supplies the current voltage for the tone generator ici3 the contact b is also closed taking the input of the transmitter in the module 1 away from the microphone 6 and connects it into the output of ici3 the exact output level is determined by r46 r47 and r48 which should be adjusted for approximately 90 modulation the contacts c will be moved to closed position to transmit the tones to be generated the capacitor c31 keeps the relays k2 energized for approximately one second permitting the operator to merely press button s1 without having to hold it in pressed position an audio sample from the control tower receiver is fed initially to four stages of programable level adjustment the first two stages r35 through r38 both inclusive are 6db attenuators and the second two ic4c ic4d and r39 through r42 both inclusive are 6db amplifiers normally these four stages will be by passed by attaching jumping wires not shown to the appropriate terminals however should the output of the receiver be too great or too small these stages can be used to adjust it the next stages are active filters formed.