Idea for frequency comparator that uses a transistor and LC oscillators

[scruffy783]

My uncle (an oldtimer who can't use computer) asked me to find a circuit design for something he called 'synchronous generator' (SG). I thought that he was talking about electric motors/generators, but he explained that SG is a device which compares two frequencies. It has an oscillator which oscillates at certain known frequency which is used to determine unknown frequency. I know how this can be done with an oscilloscope and Lissajous curves, I've been doing that myself, but he says that such circuit should only have one transistor and one or two LC oscillators.

I cannot even try to search the Internet because I don't know the name of this device, if it exists at all. Help me please.

 

[mister_rf]

Re: Frequency comparator

The Beat-Frequency Oscillator BFO may be used for this purpose.
To produce an AF output signal, you must heterodyne (beat) a signal with an RF signal of the proper frequency. This separate signal is obtained from an oscillator known as a beat-frequency oscillator. When you vary the BFO control, you are varying the output frequency of the BFO and will hear changes in the tone of the output audio signal.

 

[BradtheRad]

Re: Frequency comparator

Is your uncle wanting to listen to short wave radio?

Certain types of broadcasts use single-side-band. They sound garbled on low-end receivers.

A BFO (per mister_rf, preceding post) is needed to hear them properly. The oscillator has to be in the radio receiver circuitry.

A deluxe short wave radio will have a BFO. It's adjusted by a knob on the front (mine is, anyway).

LC oscillators implies coils and capacitors. Sine wave.

Never heard of a synchronous generator that does what your uncle describes. Maybe your uncle means 'sinewave generator'?

Look up Colpitts, Clapp, Hartley, etc. These use one transistor.

It will take some work to obtain (or fabricate) the right coils. Nowadays there are easier ways to make a sine-wave oscillator.