Unsupervised Detection of HighFrequency Oscillations Using Circuit Diagram \$\begingroup\$ @Parisa if you need better performance (performance not stated in question) then choose a better VCO. The point of this answer was to show what is possible. This topology (i.e. using a PLL) is probably going to give the best results for most applications but, if you are not too bothered about centre-frequency drift, look for a VCO that has much finer tuning and run it open loop
First, start with a high-frequency oscillator circuit that generates a square wave or DC pulse. We chose TTL digital IC because it works flawlessly at a high frequency of up to 20MHz. The circuit below is a simple crystal oscillator circuit using 74LS04 as a main component coupled with a crystal and two resistors instead of an RC network circuit.
9.3: Single Chip Oscillators and Frequency Generators Circuit Diagram
The output signal of the RF generator is an analog sine (AM modulated or not modulated ) signal. At high frequencies its amplitude decreases a lot. To be able to measure the frequency of the signal with the frequency counter a pre-amplifier / signal form shaper is needed. I took the circuit presented here and soldered it on small perfoboard.
The PLL can only remain in lock with the reference oscillator by producing the same frequency out of the divider. This means that the VCO must generate a frequency \(N\) times higher than the reference oscillator. We can use the VCO output as desired. In order to change the output frequency, all that needs to be changed is the divider ratio.
Generating high frequency sine wave (up to 100MHz ... Circuit Diagram
This generator should be able to sweep through a range of frequencies and the range would be 150 KHz to 80 MHz. the sweep rate is not more than 1.5*10^-3 decades/s. There are different oscillator topoplogies, but I can't use, say a purely RC oscillator or a crystal oscillator as they offer a static method of generation (single frequency).
