Hi I'm interested in building receivers that some of you have built yourself. I am also looking for in depth information on the operation of such receivers that is specific to a circuit diagram. I would like to drive an 8ohm speaker, other than that the more basic the better.

Regards,

 

A radio receiver needs to have high sensitivity to receive distant stations but have automatic gain control so that it is not overloaded by strong local stations.
It needs to have many LC tuned circuits for good selectivity so that you do not hear a few stations at the same time with interference from them.
A basic circuit has poor sensitivity and is overloaded by strong local stations. It receives a few stations at the same time with interference.

 

FM receivers generally include a limiter stage to get a constant amplitude signal and eliminate any AM.

 

Here is a kit with all the pieces to understand a FM AM radio.

 

A radio receiver needs to have high sensitivity to receive distant stations but have automatic gain control so that it is not overloaded by strong local stations.
It needs to have many LC tuned circuits for good selectivity so that you do not hear a few stations at the same time with interference from them.
A basic circuit has poor sensitivity and is overloaded by strong local stations. It receives a few stations at the same time with interference.

I've been working with AM to simplify frequency problems. I was able to make my own inductors and capacitors and upon calculation I tuned to a reasonable range. There was no interference from other stations that I could detect and the baseband signal was intact (everything sounds as it was recorded), however there was also a constant mixture of "hums" ie. several simultaneous frequencies of which I suspect may include harmonics of 60hz and I'll be performing some basic auditory tests eventually as well as operating on batteries. I'm yet to improve on my best design as it was a fluke from a real circuit and is now forgotten! All I can remember was a simple germanium diode detector going into a lm386 with the antenna tied to the inverting input but don't quote me on that.

I suspect some artifacts of my designs to be and would greatly appreciate clarification on..

1) I used premade china inductors (1uH, 1mH etc) instead of making one

2) I wound air core inductors

3) I wound onto a ferrite torroid with only the torroid dimensions known

4) Plenty of capacitative and inductive coupling due to poor layout on a breadboard

5) I made a variable capacitor with aluminum foil

6) I used a spool of 22 gauge magnet wire as the antenna, there is more than a meter still on the spool


I will try to replicate the circuit which worked best as I am interested in problem solving because I was otherwise happy with the quality of the baseband. I tried a number of lowpass filters and the like so perhaps one of you could test my circuit when I prepare the diagram and tell me what's missing.

Regards,

 

You made an extremely simple "crystal radio".
It is missing all the important parts in a real AM radio.

 

You made an extremely simple "crystal radio".
It is missing all the important parts in a real AM radio.

I figured that much.. I'm starting to think many users on this forum would rather point out the obvious / redirect elsewhere instead of purpose an in depth analysis on basic concepts. Clearly I need to research much more myself instead of asking for clarity on aspects that are missing in my understanding...

 

Hello,

Peter Vis has quite some schematics available:
Here is a google image link:
am/fm radio schematic petervis

Bertus