Tuning the radio receiver

Question

I am trying to understand how exactly to tune the Superhet receiver. In my simulations, I have attached to the initial frequency mixer---> A local oscillator and an AC signal source to model the incoming frequency.

Now my question is how will this wanted frequency reach the mixer from the antenna ( Since antenna is exposed to all frequencies ) ?

Do i need to add an additional tuning circuit or will this be sufficient ?

If an additional tuning circuit is needed, how will I co-ordinate the oscillators attached to them ( since both of them will require different frequency).

I believe gang capacitors come into this play ( not sure) but I have only this piece available ( nothing else) :

http://www.petervis.com/electronics/tuning-capacitor/tuning-capacitor.html

Answer 1

What you have drawn is a demodulator (it can also be used as a modulator and therefore acts as a mixer). Before the demodulator is usually an intermediate frequency (I.F.) circuit that is tuned to a fixed frequency and has several stages of band pass filtering in order to reject out-of-band (unwanted) signals.

Before the IF strip is usually the mixer - this mixes the broad array of signals from your antenna (loosely band-limited) to the intermediate frequency for filtering by the IF strip.

Tuning is done mainly on the IF strip and setting it up is usually an iterative process.

BTW - using 1N4007 diodes will not yield great results because of their slow response - try a BAS16 or 1N4148 - they are much quicker and if you want to run your mixer at beyond 1 GHz, there are others you can choose.

Answer 2

The main feature of the superheterodyne is that tuning is done at the IF stage, not at the carrier frequency stage.

The output of your frequency mixer should go into a bandpass filter. To tune the receiver, you simply change the local oscillator -- the bandpass filter remains fixed.

Wikipedia has a great article on the superheterodyne receiver. Consulting the block diagram would have answered your question.