frequency readout circuit

[mstechca]

I want to make a circuit that can tell me exactly what frequency any receiver (whether regenerative or heterodyne) can pick up. How difficult is this task, and how do I start?

As soon as I know the theory behind it, I think I can make one.

 

[David Bridgen]

You need a frequency counter.

With a regen receiver you would need an amplified and filtered signal from the feedback loop.

With a superhet you would need to subtract the i.f. from the local osc. frequency and measure that.

 

[k7elp60]

For the heterodyne type all the systems that I am aware of measure the local oscillator and either add or subtract the IF frequency depending on wether the local oscillator is below or above the received frequency. The normal is to have the local oscillator above the received frequency + the IF frequency, but I have seen it the other way where the local oscillator is below the received frequency - the IF frequency.

I am not sure how you would do it for a regenerative receiver, as the detector is actually oscillating near the received frequency.

I bought an assembly several years ago from a fellow that built some assemblies that does exactly what I described for the hetrodyne type receiver. I'll see if I can find the information for it. It was good for a great range in received frequencies and IF frequencies.

 

[mstechca]

You need a frequency counter.

With a regen receiver you would need an amplified and filtered signal from the feedback loop.

I have an amplified signal.

How do I make a frequency counter? do I mix a 4040 counter chip with something? Is there some simple block-diagram circuit you can show me?

 

[audioguru]

I don't think a 4040 will count VHF FM broadcast band frequencies with its very limited high frequency counting ability. Besides, it is a ripple counter so its outputs aren't syncronized.

 

[David Bridgen]

Is there some simple block-diagram circuit you can show me?

This is a (very basic) block diagram of a counter.

Its simplicity is deceptive. If you want to build one I suggest buying a kit.
There are some available which have the offset facility which is necessary to measure the input frequency of a superhet receiver.

Google searches can reveal much useful information.