Measurement of Frequency

[remon7]

there have many methods for frequency measurement. Most of the method comparing for unknown signal against a standard signal. so How can i evaluate both unknown frequency?

 

[alec_t]

You must have a reference frequency or time period to determine an unknown frequency.

 

[crutschow]

Typically a crystal oscillator is used to generate the reference standard frequency.

 

[dr pepper]

Thats an interesting question, beats me.
Might be a question for the mathematically minded, if at least one of the freq's is stable there might be a way.

 

[ronsimpson]

there have many methods for frequency measurement. Most of the method comparing for unknown signal against a standard signal. so How can i evaluate both unknown frequency?

Please define "evaluate". What do you want to know? The ratio of the two frequencies? The difference? The stability?
To measure anything you need to know something. You need a reference? You need a starting place.
When measuring temperature you start out with freezing and boiling and compare your temp against these points. OR start at absolute zero and some other point.

 

[ChrisP58]

You really can't measure anything, unless you have some known, stable reference to compare it to.

 

[unclejed613]

you must have a "known" in order to measure an "unknown".... you can compare two "unknowns", but it's only a relative comparison. so you have "unknown-1" and "unknown-2", and you can compare them to find that "unknown-2" is twice the frequency of "unknown-1", but to actually KNOW the frequency of one or the other, you need to compare them with an objective standard. with your "unknowns" you can even have extremely high precision (i.e. repeatability), but not accuracy. now if you add a 10Mhz time base, and compare the unknown with it, now you know what the frequency is....