Will this simplest AM receiver work in theory or even in practical?

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Willen

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-Its detected current has few nA and few nV. And also there is voltage drop exist across diode. How this can work and play station without any external power source (battery)?

-What is the minimum and maximum level of current and voltage needed for crystal earphone to operate?

- Cannot we make FM receiver like this method? Why?

Thanks in advance!
 

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I suggest you google 'crystal set' - which is what that circuit is - a VERY, VERY common radio receiver circuit in the distant past, and fully workable.
 
Nigel Goodwin said:
I suggest you google 'crystal set' - which is what that circuit is - a VERY, VERY common radio receiver circuit in the distant past, and fully workable.
Click to expand...

yup indeed it is

I made my first oe when I was ~ 8 years old
and that's going back more years than I care to remember

Dave
 

I remember reading (back in 70's) that you could run a small electric car with such a setup (motor instead of earphones) around Thule, Greenland - thanks to the Very High Power Radar and Communication transmitters!

Ramesh
 
Willen said:
.............................

- Cannot we make FM receiver like this method? Why?
Click to expand...
Generally you can't make an FM receiver that way since it requires more complex processing to recover the FM modulation from the carrier and this requires more power than can be readily extracted from the RF input. An AM receiver only requires a simple detector (rectifier) to recover the AM modulation which can operate from the antenna power generated by a local AM station.
 
There are many FM Crystal Radio projects in Google. They are basically a simple AM radio tuned to the FM broadcast band. The FM is demodulated using slope detection (tune the radio to one side of a station).
 
- Can I use Schottky diode (like 1N5711) instesd of germenium (like 1N34) as a detector (rectifier)? Which one is better? Germenium is little expensive here and I think Schottky are little cheap.

- I searched various crystal sets which is self powered. And they need too long antenna and compulsory earth connection. So it is not portable. Can't we make simple portable self powered AM detector ?
 
If there is a very powerful AM or FM radio station beside you then the crystal radio can be portable.
 
Willen said:
Can't we make simple portable self powered AM detector ?
Click to expand...

Generally no. It requires a certain amount of radio energy from the station that is sufficient on long aerials and a good ground. However a small coil inside a box doesn't get enough energy from the radiated signal to overcome the diode drop and drive the headphones unless you are really close to the transmitter.

https://en.wikipedia.org/wiki/Antenna_aperture

Or in simple terms, small aerials get less power and in the case of a crystal set, this power is needed to power the headphones as you cannot actively amplify the signal without an external battery.
 
audioguru said:
There are many FM Crystal Radio projects in Google. They are basically a simple AM radio tuned to the FM broadcast band. The FM is demodulated using slope detection (tune the radio to one side of a station).
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what? You mean- such AM detector can receive FM radios? I found- some one is saying it is possible using such basic detector!!! https://solomonsmusic.net/FM_CrystalRadio.html

How it is possible to demodulate FM signal like AM?

I think it is not possible to hear FM witout external power source like AM detector, can we?
 

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A AM detector does not receive FM (well at all). But it can if things are just right.
>>>If the Q of the LC filter is high.
>>>If the AM detector is tuned off to the side of the FM signal.
>>>Strong signal.
With FM the frequency moves to send information. (audio) Because the amplitude does not change a AM detector will not see the audio.
With AM the amplitude changes to send information.
If the AM radio is tuned off to the side of the FM signal, then when the frequency moves UP/DOWN it will get closer/farther away to the frequency the radio is tuned to. As the signal moves away the signal looks weaker. As the signal moves closer it looks stronger. So it is possible to hear FM on a AM radio. (not well but...)
 
As audioguru says, receiving of FM signals by Slope Detection is possible.

You need to have strong signals (either by Proximity or Amplification). It's quite simple for receiving Narrow Band FM. A lot of hobbyists use this technique for listening to Police / Airport / Band 1&3 TV Broadcasts.

FM broadcast can also be similarly received, but Low Q coils need to be used because of the Wide bandwidth of 150 KHz.

Ramesh
 
Nice explanation of ronsimpson!

But being puzzle ronsimpson said "need high Q coil" and Ramussons said "need low Q coil".

I think low Q coil for FM detection is known here as High Q!
 
Slope detection is used to hear FM from an AM radio. You tune the radio to one side of the carrier so the amplitude varies as the frequency varies.
But since the slope of an LC tuned circuit is not linear and an AM detector diode also is not linear then a lot of distortion is produced. Since the extremely simple "crystal radio" does not have de-emphasis then distortion is increased.

I have never seen "crystal" headphones. Maybe they are piezo types. Then they are activated by very low power. Of course the FM radio station must be very powerful and be close to your crystal FM radio.
 
audioguru said:
I have never seen "crystal" headphones. Maybe they are piezo types. Then they are activated by very low power.
Click to expand...

hehehe Yes, I mean 'Crystal ear piece'. I've seen this type of Crystal earpiece used on hearing device for deaf person.
 

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Willen said:
Nice explanation of ronsimpson!

But being puzzle ronsimpson said "need high Q coil" and Ramussons said "need low Q coil".

I think low Q coil for FM detection is known here as High Q!
Click to expand...

I think the attached figure should explain.

Ramesh
 

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another good detector would be a silicon carbide (SiC, also known as carborundum). with a SiC detector, you will need a local battery to bias the junction to just below it's conduction threshold (actually this method works with silicon and germanium diodes as well, but the threshold voltages are lower). this is the technique used by the Marconi company back in the early 20th century. the bias is supplied through very large (1Meg) resistors, so that the battery doesn't act as a low impedance path for RF across the diode.

SiC has the added advantage of ZERO reverse recovery time, which makes it work better at high frequencies.

EDIT: SiC Vf=2V, Ge Vf=0.3V, Si Vf=0.7V
 
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It is also possible to build a true FM detector using two diodes and a 90° phase shift arrangement to make a quadrature detector. I built one a few years ago with a helical resonator (unloaded Q of about 2000, and loaded Q of about 500).

It works quite well picking up all the local stations with an indoor dipole antenna. I did a detailed writeup on it:
**broken link removed**
 
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