I was building the superhet receiver for ham radio. But I seem to have got stuck at the demodulation stage.
As an example:
Suppose the person is transmitting SSB signal (20m band) at 14.250 MHz carrier frequency.
Let the speech signal occupy 1KHz bandwidth.
So the RF signal using Upper Side Band is 14.251 MHz.
I take intermediate frequency of 455 KHz.
So my Local oscillator is set to 14.251 + 0.455 = 14.706 MHz.
Now at the demodulator, the 455 KHz wave is needed to be demodulated. For this particular example, the oscillator frequency I need to inject in demodulator is 456 KHz (to recover 1 KHz speech).
Firstly, am I going wrong somewhere till now?
Secondly, in real situation, I would not be knowing this much information. The only thing I would be knowing is that my Mixer oscillator is set to 14.706 MHz. So the Rf freq must be 14.251 MHz. Now here is the problem:
This 14.251 MHz could be a 14.250 MHz carrier with 1 KHZ sideband or it can be a 14.249 MHz carrier with 2 KHz sideband or any other pair of values. So how do I demodulate?
In other words, how do I know what frequency to inject in the demodulator? Do I just keep tuning the oscillator attached to the demodulator until the combination is struck?
If yes, then wouldn't finding any random person over this wide range of band quite painful; First you set the Mixer oscillator to some value and then you keep tuning the demodulating oscillator over the entire 3 or 4 KHz bandwidth until you find someone?