Radio frequency alarm system including transmitting, coding and decoding circuitry

A frequency detector for detecting the occurrence of a predetermined chosen band of frequencies in an electrical signal component which includes a train of relatively short pulses which may occur at a frequency or repetition rate above, below or within said band of frequencies, said frequency detector comprising:

• first and second toggling means connected to receive said signal component and to toggle between two output states as a function of the frequency of said one signal component wherein both toggling said toggline means are caused to toggle or not to toggle whenever the frequency of said signal component is above or below said predetermined chosen frequency band and wherein only said first toggling means is caused to toggle whenever the frequency of said one signal component is within said predetermined chosen frequency band, and
• toggle detecting means connected to said first and second toggling means for detecting the condition wherein only said first toggling means is toggling and for producing an output in response to such detection thereby indicating the presence of a frequency within said predetermined frequency band in said signal component,
• said first and second toggling means including:
• a first input circuit means connected to receive said signal component and to be returned to a predetermined starting state at the frequency of said one signal component wherein said input circuit means is caused to progressively change its state as a function of elapsed time between such returns to its starting state,
• a divider circuit means connected to provide first and second predetermined different reference signals which bracket a corresponding predetermined range of variation in the state of said first input circuit means,
• a first comparator means having one input connected to monitor the state of said first input circuit means and having another input connected to monitor said first reference signal whereby said first comparator means is caused to toggle between two output states whenever the frequency of said one signal component is within or below said predetermined chosen frequency band which band corresponds to said predetermined range of variation in the state of said first input circuit means, and
• a second comparator means having one input connected to monitor the state of said first input circuit means and having another input connected to monitor said second reference signal whereby said second comparator means is caused to toggle between two output states whenever the frequency of said signal component is below said predetermined chosen frequency band but to otherwise remain stable at a first output state.

A frequency detector for detecting the occurrence of a predetermined chosen band of frequencies in an electrical signal component which includes a train of pulses which may occur at a frequency or repetition rate above, below or within said band of frequencies, said frequency detector comprising:

• a timing circuit connected to receive said train of pulses and to provide a time dependent signal during intervals between individual pulses;
• a first comparator connected to compare said time dependent signal with a predetermined first reference signal during intervals between individual pulses and to provide one or the other of two output signals depending upon the relative magnitudes of the compared signals;
• a second comparator connected to compare said time dependent signal with a predetermined second reference signal during intervals between individual pulses and to provide one or the other of two output signals depending upon the relative magnitudes of the compared signals;
• and
• a detector circuit connected to receive the output signals from said first and second comparators and to provide an output indicating the presence of said band of frequencies as a function thereof.