Minimal radio receiver?

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
Hi I would like to build the most basic radio receiver possible. Ideally I would like a large bandwidth that I can listen on regardless of the encoding (AM/FM) but either AM or FM is great. I have reviewed a number of circuits and I am unclear on how the data is extracted from the carrier with simple radio circuits with just a few transistors.

I imagine a simple circuit to include: antenna, tank circuit, demodulator and amplifier. Any clarification on the the subject is most appreciated.

Regards,
 

Yaakov

Joined Jan 27, 2019
3,153
Just a point, AM and FM are modulation not encoding. It's in the name.

The detectors for each modulation scheme are different, you would need two. The antennas and tank circuits are resonant components with limited bandwidth, you will need more than one to handle various frequency ranges.

Why do you have this particular specification? It's not very practical.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
These two goals are contradictory.

Bob
Can you elaborate? I'm building this circuit to hear and see with a scope what's being broadcasted locally before the demodulator has a chance at it and then see what the demodulator did to the signal. Imagine for example an army trying to intercept radio signals, surely they have equipment that can listen on all bands to start to code breaking process.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
Just a point, AM and FM are modulation not encoding. It's in the name.

The detectors for each modulation scheme are different, you would need two. The antennas and tank circuits are resonant components with limited bandwidth, you will need more than one to handle various frequency ranges.

Why do you have this particular specification? It's not very practical.
I reviewed the terms and I thought they were synonymous :). I understand that each circuit is tuned to a specific frequency range and demodulation scheme. I am curious to the effect on any one receiver circuit if there is an equal power incoming carrier of the same frequency containing another type of modulation. This interest is off topic but nonetheless applicable.

I should note I would like to drive an 8ohm 350mV speaker.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
That would be an AM receiver using a cat whisker. It's very simple actually. (It doesn't necessarily need a power source either!)

View attachment 240291
This is one of the circuits I found. I understand the components left of the diode. Can you explain how the diode and capacitor are demodulating the signal to output the data in the audible frequency range? The circuit I found uses a germanium diode and a special earphone. I was planning to adapt this circuit to a speaker via amplification.
 

andrewmm

Joined Feb 25, 2011
1,466
Can I just ask,
without prejudice
do you want to build this into your head ?
( sorry if you don't, some one once did )

So,
radio itself is simple,
a bit of wire in the air will receive,
however you wont be able to listen , as you have no selectivity, means do select one frequency over another.
no amplification of the very weak signal
no "demodulation" , single side band , AM, FM, PM, Dab et all.


"simplest" , if your interested in the decoding / listening side
is possibly a soft ware defined radio, as you need a pc to use, certainly not simple to build,
but available from around USD30 , and very wide coverage range.
 

sparky 1

Joined Nov 3, 2018
541
Dick Cappels had commented early morning tuesday on AM radio circuit using IC ZN414 MK484. Looks like one of his projects from 2003.
The advantage to that he can answer questions about it. Was that Manhattan or dead bug style pcb ?
I think the idea is commonly overlooked needs more innovative type experimentors. a link to his post here:
https://forum.allaboutcircuits.com/...rphones-for-crystal-radio.179521/post-1636292
 
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