Digital frequency counter

  
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The frequency measurement is one of the most important things in radio construction. Without it you will be unable to set desired frequency in your receiver (and in transmitter too!), without it you will be unable to monitor frequency drifts etc. Sometimes, frequency counter can be used to verify, whether the oscillator works and ensure the stabil
Digital frequency counter - schematic

ity of the generation. Measurement of the frequency with ultimate precision, compared to other measurements is incredible simple. You may easily measure 1 MHz frequency with resolution 0. 1 - 1 Hz and precision up to 1-5 Hz. Could you measure 1V with precision 5 microvolts I think, no and never! The idea of frequency measurement is quite simple - you just count the number of impulses during fixed time interval. If the time interval has length 1 second, the result will be directly in hertz. The precision is determined only by precision of time intervals, but the latter are usually formed from high-stable quartz oscillator. Typical counter consists on the following parts: reference oscillator, counter with indication, input trigger and control circuits. Reference oscillator together with control circuits forms fixed time interval as well as reset impulses for counters. The input signal passes through input amplifier and trigger, becoming the levels used by ICs. Then the impulse sequence formed goes to the `gate`, which periodically opens for precise time determined by control circuit. During this time, counters accumulate the result, which is displayed. The structure diagram of my unit is shown below: In my unit to add to all standard parts internal memory triggers are introduced to make measurements more convenient and fast. If output indicators are connected directly (trough corresponding decoders) to the counters, the...



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