1 kHz - 100 MHz frequency measurement

[per_lube]

Hi all,

I got a down-converted signal from an RF front-end and the frequency of the down-converted signal varies from 1 kHz -100 MHz.

I need to know the frequency of the down-converted signal and take some decisions based on the frequency in an electronic circuit.

I found some frequency-to-voltage converter chips (such as LM2917) which works only up to 500 kHz - 1 MHz.
I can use this one to measure up to 1 MHz, but I need to measure frequencies up to 100 MHz.
I don't need a very accurate frequency measurement.

Could anyone suggest a method to perform this?

cheers,
per_lube

 

[FvM]

The output signal of a RF front end is rarely a single frequency that can be measured with a frequency counter or f/V converter. Even if it is mostly a single frequency, you need to think about level range and signal-to-noise ratio.

A prescaler (frequency divider) is the usual way to get a frequency range that be measured with a frequency counter or similar.

 

[per_lube]

Thanks for the reply FvM.

Does it require to feed a square wave to the prescaler or is it possible to directly feed the sinosoidal signal which comes out from the RF front-end?

 

[FvM]

The question must be answered for specific prescaler devices. Many of it have a kind of built-in preamplifier and signal shaper, so they can work with signal levels (usually sine) of several 10 or 100 mV. But for a meaningful frequency measurement, the signal must be spectrally clean, not a mixture of different signal components.

 

[crutschow]

You could perhaps use some sort of spectrum analyzer circuit to determine the frequency components.

 

[Borber]

Here is a project of a suitable frequency counter for that frequency range: http://lea.hamradio.si/~s53mv/counter/counter.html just to give you an idea. Althou I think that spectrum analyser is better if measured signal is complex and not single frequency.