Ultra high speed scan system

In a high speed scanning radio receiver having an RF amplifier, a frequency synthesizer for generating a local oscillator signal, a mixer receiving an input from the RF amplifier and the local oscillator signal from the frequency synthesizer, an IF amplifier receiving an input from the mixer, a demodulator for demodulating an IF signal from the IF amplifier and providing an output signal to an audio output stage, the improvement comprising:

• memory means for storing a plurality of frequency codes corresponding to respective radio channels;
• scan control means for sequentially reading frequency codes for each channel to be scanned from said memory means and for loading said frequency synthesizer with said sequentially read frequency codes;
• means utilizing said frequency codes to generate a local oscillator signal;
• means for sensing each scanned channel to detect the presence of a signal on the channel;
• and
• squelch circuit means for disabling said audio output stage in the absence of a detected signal on any one of the channels corresponding to said frequency codes, the squelch circuit means being deactivated and the scan control means interrupted upon detection of the presence of a signal on a channel, said squelch circuit means comprising a multi-order filter, noise diode detector, a multiplexer, an analog to digital converter, means for storage of successive average values of noise, and means for comparing those successive noise values with one another to provide a noise difference and for comparing successive noise difference with a predetermined squelch control value, detection of the presence of a signal on a channel being indicated when successive noise differences exceed the predetermined squelch control value.

In a high speed scanning radio receiver having an RF amplifier, a frequency synthesizer for generating a local oscillator signal, a mixer receiving an input from the RF amplifier and the local oscillator signal from the frequency synthesizer, an IF amplifier receiving an input from the mixer, a demodulator for demodulating an IF signal from the IF amplifier and providing an output signal to an audio output stage, the improvement comprising:

• memory means for storing a plurality of frequency codes corresponding to respective radio channels;
• scan control means for sequentially reading frequency codes for each channel to be scanned from said memory means and for loading said frequency synthesizer with said sequentially read frequency codes;
• means utilizing the frequency codes to generate first and second local oscillator signals;
• means for sensing each scanned channel to detect the presence of a signal on the channel;
• and
• squelch circuit means for disabling said audio output stage in the absence of a detected signal on any one of the channels corresponding to said sequentially read pair of frequency codes, the squelch circuit means being deactivated and the scan control means interrupted upon detection of the presence of a signal on a channel.