Checked if 2 diodes demodulator can decode FM/AM modulated radio without LC tuned circuit

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[Abstract]

I saw an experiment of decoding FM signal by using 2 crystal diodes named
  "Simple FM crystal radio"   (a video on the internet).

I checked if  2 diodes demodulator can decode FM/AM modulated radio without LC tuned circuit.

[Result]
(1) Decoding AM can be possible when the signal is very strong.
(2) Decoding FM is very difficult even though the signal is very strong.
(3) For FM commercial station from 76[MHz] to 108[MHz] is almost impossible.
(4) As an experiment, it is very interesting.  :-)


1. Decoding AM radio station when the signal is very strong


[Result]

Fig. 1.1 and Fig. 1.2 are the transient analysis for AM modulated signal.

It can decode AM modulated signal when the signal is very strong. 

However, it may be difficult to say it is practical.

Fig. 1.1 decoding AM modulated signal (with wide range FFT)

Fig. 1.2 decoding AM modulated signal (with narrow range FFT)

2. Decoding FM radio station when the signal is very strong


[Result]
Fig. 2.1 and Fig. 2.2 are the transient analysis for FM modulated signal of 10.7[MHz].
Baseband frequency is 1[KHz] here.

This result may imply FM modulated signal on 10.7[MHz] used as IF frequency may decode it when the signal is very strong.

However, demodulated signal output is very weak and the tone quality is not good. 

Fig. 2.1 decoding FM modulated signal (with wide range FFT)

Fig. 2.2 decoding FM modulated signal (with narrow range FFT)

3. Characteristics of F/V (Frequency to Voltage) convertor or P/V (Phase to Voltage) 

Fig. 3.1  F/V F/P characteristics (Gain and Phase on 5[MHz] to 200[MHz]) 

Fig. 3.2  F/V F/P characteristics (Gain and Phase on 7.7[MHz] to 15[MHz]) 

Fig. 3.3  F/V F/P characteristics (Gain and Phase on 47[MHz] to 61[MHz]) 

Fig. 3.4  F/V F/P characteristics (Gain and Phase on 68[MHz] to 108[MHz]

(FM band for commercial broadcast stations band) 

This 2 diode decoder has very small characteristics of F/V (Frequency to Voltage) convertor or P/V (Phase to Voltage) .

Because there is very small linear FM/PM decoding capability on Fig. 3.1 to Fig. 3.4.

However, output voltage is very tiny and it is almost impossible to decode FM stations on the band from 76[MHz] to 108[MHz].

Fig. 3.1  F/V F/P characteristics (Gain and Phase on 5[MHz] to 200[MHz]) 

Fig. 3.2  F/V F/P characteristics (Gain and Phase on 7.7[MHz] to 15[MHz]) 

Fig. 3.3  F/V F/P characteristics (Gain and Phase on 47[MHz] to 61[MHz]) 

Fig. 3.4  F/V F/P characteristics (Gain and Phase on 68[MHz] to 108[MHz]

(FM band for commercial broadcast stations band) 

Reference:

[1] "Simple FM crystal radio"a video on the internet.

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