What is a Frequency Counter
Frequency counters are test instruments used to provide very accurate measurements of the frequency of a signal.
Frequency counters are test instruments used in many applications associated with radio frequency engineering to measure the frequency of signals very accurately.
These frequency counters and counter timers are widely used within a variety of areas to measure the frequency of repetitive signals, and also for measuring the time between edges on digital signals.
Whilst the actual requirements and applications for RF frequency counters and timers are different, they use the same basic circuitry, with some simple internal reconfiguration and as a result sometimes RF frequency counters are also able to act as timers. Typically the very high RF frequency counters will not incorporate the timer capability.
What is an RF frequency counter: basics
In essence a frequency counter operates by counting the number of times a signal passes a give voltage point - trigger point - in a given time.
If for example the time for which the frequency counter is set to count is a second, i.e. a gate time of a second, then if a waveform crosses the trigger point a hundred times, there will be a hundred repetitions of the waveform in a second, i.e. its frequency is 100 Hertz.
If the same waveform was used, but the gate time is reduced to a tenth of a second, then only ten repetitions would be seen. The circuitry can easily accommodate this and the circuit can deduce that in a tenth of a second ten repetitions are seen, then the waveform has a frequency of 100 Hz.
RF frequency counter applications
RF frequency counters are used in very many applications where the frequencies of radio frequency or even audio frequency signals are to be measured. Some applications may include:
- Measuring the frequency of a transmitter carrier.
- Measuring the frequency of an oscillator in a circuit.
- Measure the frequency of a signal on a line
- Any application where the frequency of a steady repetitive signal needs to be measured.
To be able to measure the frequency of an RF signal using a frequency counter there are a few prerequisites.
- Frequency must be steady, i.e. not varying.
- The signal should not have modulation applied as this will prevent proper counting.
- Signal must have sufficient amplitude – typically signals over about half a volt are suitable.
- Signals should not be so large that they overload the input - check the manufacturer’s specification if in doubt.
RF frequency counters are a widely used piece of test instrumentation. They are used for many RF measurements. Although Spectrum analyzers are also able to make frequency measurements, and todays analyzers can take very accurate readings, RF frequency counters are relatively cheap and provide measurements that are equally accurate or more accurate.
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