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Need help with this FM detector circuit

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ramy gad

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Nov 6, 2005
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this circuit act as FM detector but how it works
how to design it and change it parameter according to the specification

Need help with this circuit

IFT acts as a frequency to amplitude transform. You have to tune it in the linear region of the characteristic of the transfer function of IFT. The diodes is just a square operator to get the envelope.

Need help with this circuit

where exactly

Re: Need help with this circuit

Circuit image not visible....attach as a file...

Re: Need help with this circuit

Circuit image not visible....attach as a file...

well,I can viewing the schematics, after login

Need help with this circuit

the tank circuit in the front used for FM detection called this method the linear slope detector the signal output from the tank circuit is converted from FM to AM modulated signal so we use the diodes as AM detector with the charging cap then the amplifier stage

    ramy gad

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Re: Need help with this circuit

Check this link, **broken link removed**
There, you will find out how to design an FM demodulator circuit..
I hope it helps,

    ramy gad

    Points: 2
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i think your question is stupid ! and quite terrible

in that you expect too much from others to analyze

from a single scribbled circuit complex FM

i come up with 20 such circuits every day

most of which have a flaw or two in scope.. of the field needed to do a good job

this circuit looks like something i would make as a first time affair in first year electronics and looks like an exam question

and intended as a 'crystal radio' type decoder to enhance

a homebrew 100mhz broudcast band transmition reciever

and it is far from refined...!

i see a few flaws in this 'scribble' already
and no sign of your use of simulators
to gain aspect insight
upon experimentation with your own values set's or tweaks in componentary used

as pointed out above
to learn how to do a thing

first is best !!!

then analyze others 'scribbles' with heinsight

read books man

there aint no easy answeres to rf
other than formular

its multiphasial

so learn each way to manipulate each phase in harmony

best to start with musical instument discrimination in audio

and read some books .,

some people just ask stupid questions to be told off !!!

so slap of hand go read a few book ffs...


Please do not be so harsh when posting. Sometimes things is hard to understand and we are all here to either learn or learn others. Every now and then membes need a short explanation or solution and not really to learn. I cannot judge in this matter and if it is "common knowledge" but try to keep the post clean both regarding language and otehr things.

Any comments sent by PM to me.


I think one of the diodes is backward.

Yeah, look here:
**broken link removed**

    ramy gad

    Points: 2
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how to design a wideband FM dem?
someone give any suggest.

Did you get that circuit from this page: **broken link removed** ?

Anyway, I recommend the book "Communication Circuits: Analysis and Design" by Clarke and Hess. It has a very thorough analysis of this circuit and many other analog communication circuits.

I don't think there's anything wrong with the direction of the diodes. The circuit looks to me as some variation of what is called a Null-and-Balance detector for FM. But in this type of detector which is again a modified Foster-Seeley, the input comes via a split capacitor section (in parallel with the secondary winding) rather than a split secondary winding. This is done to improve symmetry around the center frequency, which is difficult to with a split inductor where you need exact equal inductances. The parallel load resistors over the diodes is characteristic of this type of detector when used with the split capacitor input.

On the page **broken link removed** mentioned, this is how the guy describe this design:

Very Sorry! I learned about FM detection on Japanese textbook. Therefore I do not know correct English about it. Ratio detector needs a special coil designed to use FM detection. It is not easy to get it in Japan.
The detector here I introduced is called as " Wise detector" . I guess the "Wise" may be the name of the developer. This circuit do not need the special transformer. I can use 455kHz AM coil for it, only changing the frequency by adding the capacitor. By adding 470pF , the frequency of this coil becomes 244kHz. After making this circuit, I connect the signal generator on the (H) point and with changing the frequency, I noted the output voltage of this detector. Please see the right side of the circuit diagram! Here I show you the character of this FM detector.

it looks like a tuning problem to me... os please check the criteria

Oh,I have designed a very wide band FM detector by using to resonator. and the result indicate that the S curve is meet requst.

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