The SP-1a Speech Processor was developed by Clear Channel Corporation for the Ranger AR-3300 and AR3500 radios. It works well in most radios in AM FM & SSB. It is an audio processor that delivers an average of 90% modulation. It boosts lower levels to within 90% of it’s maximum output with a very low distortion.It connects in-line of the audio Mic input of the microphone jack. It also requires a 12 Volt connection in the radio. A SPST switch can be used to switch the SP-1a in and out of the circuit. When switched off the speech processor is completely out of the circuit leaving the radio back to stock audio.