Method and apparatus for monitoring frequency

Claim 3

A method as claimed in claim 1 including the additional step of discarding the highest order digits in the count of the number of cycles gated by said source of gating signals to simplify the checking of the count to see that it is within desired limits.

Claim 4

A method as claimed in claim 1 including the step of discarding low order digits in the count of the number of cycles gated by said source of gating signals in order to simplify the checking of the count to see if it is within limits, the discarded low order digits corresponding to count values which are insignificant in checking the difference frequency within the required accuracy.

Claim 5

A method as claimed in claim 1 including the additional step of subtracting a predetermined fixed number from the count of the number of cycles gated by said source of gating signals to derive a difference count number in the order of magnitude of a number representing the maximum desired range of variations of the difference between the frequencies of said two different frequency sources.

Claim 6

Apparatus for monitoring the frequency value of a high frequency signal comprising a modulator arranged to receive the signal to be monitored, said modulator being arranged to receive a standard frequency to be compared with the frequency to be monitored, means for deriving from said modulator a difference frequency corresponding to the difference between the frequency to be monitored and said standard frequency, a gate control means operable to receive the difference frequency signals and operable to generate gating signals each having time periods of duration based upon the time period of a predetermined number of cycles of said difference frequency, a logic gate device connected to be enabled by said gating signals, said gating device being connected to receive frequency signals from a standard frequency source, a digital counter connected to receive the standard frequency signals gated through said gating device and to register a count of the number of cycles of said standard frequency gated through said gating device, and count detector means connected to said counter and including digital logic circuitry operable to determine whether or not the registered count is within predetermined limits corresponding to a desired range of values for the monitored frequency.

Claim 7

Apparatus for monitoring the frequency value of a high frequency signal comprising a modulator arranged to receive the signal to be monitored, said modulator being arranged to receive a standard frequency to be compared with the frequency to be monitored, means for deriving from said modulator a difference frequency corresponding to the difference between the frequency to be monitored and said standard frequency, a gate control means operable to receive the difference frequency signals and operable to generate gating signals each having time periods of duration based upon the time period of a predetermined number of cycles of said difference frequency, a logic gate device connected to be enabled by said gating signals, said gating device being connected to receive frequency signals from a standard frequency source, a digital counter connected to receive the standard frequency signals gated through said gating device and to register a count of the number of cycles of said standard frequency gated through said gating device, and count detector means connected to said counter and including digital logic circuitry operable to determine whether or not the registered count is within predetermined limits corresponding to a desired range of values for the monitored frequency.

Claim 8

Apparatus for monitoring the difference between the frequencies from two different frequency sources comprising a modulator arranged to receive the frequencies from said two different frequency sources and operable to derive a frequency corresponding to the difference between the frequencies from said two different sources, a gate control circuit connected to receive the difference frequency and operable to issue periodic gating signals each having a time period based upon the time period of a predetermined number of cycles of the difference frequency, a gating device connected to receive said gating signals, said gating device being arranged to receive signals of a known frequency to be gated through said gating device by said gating signals, a digital counter connected to the output of said gating device and operable to count the number of cycles of the known frequency gated through said gating device during a gating time period, and count detector means connEcted to said counter and including digital logic circuitry operable to determine whether or not the registered count is within predetermined limits corresponding to a desired range of values for the difference frequency.

Claim 9

Apparatus for monitoring the difference between the frequencies from two different frequency sources comprising a modulator arranged to receive the frequencies from said two different frequency sources and operable to derive a frequency corresponding to the difference between the frequencies from said two different sources, a gate control circuit connected to receive the difference frequency and operable to issue periodic gating signals each having a time period based upon the time period of a predetermined number of cycles of the difference frequency, a gating device connected to receive said gating signals, said gating device being arranged to receive signals of a known frequency to be gated through said gating device by said gating signals, a digital counter connected to the output of said gating device and operable to count the number of cycles of the known frequency gated through said gating device during a gating time period, and count detector means connEcted to said counter and including digital logic circuitry operable to determine whether or not the registered count is within predetermined limits corresponding to a desired range of values for the difference frequency.

Claim 10

Apparatus as claimed in claim 6 wherein said gating device is connected to receive one of the frequencies from said two different frequency sources to serve as the known frequency gated through to said digital counter.

Claim 11

Apparatus as claimed in claim 7 wherein a pulse shaper is connected to the input of said gate device which is arranged to receive said known frequency so as to provide substantially square wave pulses at said known frequency to said gating device.

Claim 12

Apparatus as claimed in claim 6 wherein said gate control circuit includes a frequency divider operable to divide said difference frequency to provide gating signals based on the division and having a period equivalent to a plurality of cycle periods of said difference frequency.

Claim 13

Apparatus as claimed in claim 6 wherein said digital counter includes a reset means for resetting said counter when a new count is to be taken.

Claim 14

Apparatus as claimed in claim 6 including a circuit connection from said gate control circuit to said count detector for enabling said count detector with a store signal to read and transfer the count value within said digital counter to said count detector.

Claim 15

Apparatus as claimed in claim 11 wherein said counter includes a reset means for resetting said counter when a new count is to be taken, said gate control circuit including means connected to supply a counter reset signal to said counter reset means after the emission of a store signal to said count detector.

Claim 16

Apparatus as claimed in claim 11 wherein the connections from said digital counter to said count detector are limited to predetermined low order digit signal connections to thereby discard high order digit portions of the count value within the digital counter having known count values.

Claim 17

Apparatus as claimed in claim 11 wherein said count detector includes means for subtracting a fixed number from the count stored in said digital counter in order to reduce the size of the net number to a small digital value for greater ease in determining the correctness thereof.

Claim 18

Apparatus as claimed in claim 14 wherein said count detector includes a register connected to receive the net number from said subtractor and to store that number for further reference.

Claim 19

Apparatus as claimed in claim 15 wherein said digital logic circuitry comprises logic gates connected to output connections from said register for detecting whether or not the net count value stored in said register is within desired limits for emitting a signal indicative thereof.

Claim 20

Apparatus as claimed in claim 6 wherein said modulator comprises a balanced modulator for deriving said difference frequency.

Claim 21

Apparatus as claimed in claim 17 wherein a filter is provided between said modulator and said gate control circuit, said filter being a low pass filter for passing only the difference frequency.

Claim 22

Apparatus as claimed in claim 18 wherein a pulse shaper is connected in circuit between said filter and said gate control circuit for providing a substantially square wave to said gate control circuit at said difference frequency.