FM: Foster-Seeley discriminator

transistor495 · Jan 7, 2009

This wikipedia explanation tells nothing. Anyone have a detailed explanation of the circuit. I didn't understand the underlined portion.

It uses a tuned RF transformer to convert frequency changes into amplitude changes. A transformer, tuned to the carrier frequency, is connected to two rectifier diodes. The circuit resembles a full-wave bridge rectifier. If the input equals the carrier frequency, the two halves of the tuned transformer circuit produce the same rectified voltage and the output is zero. As the frequency of the carrier changes, the balance between the two halves of the transformer secondary changes, and the result is a voltage proportional to the frequency deviation of the carrier.

ericgibbs · Jan 7, 2009

transistor495 said:
This wikipedia explanation tells nothing. Anyone have a detailed explanation of the circuit. I didn't understand the underlined portion.

hi BC,
The small voltage generated due being 'off tune' is used to correct the tuning, usually a varicap.
Is this what you mean.?
Or
Are you asking about the way the ratio detector demodulates a FM carrier.??

OK.?
This is a better description:
**broken link removed**

transistor495 · Jan 7, 2009

Eric,
I didn't understand a single word u told. Please give me a detailed explanation.
When the input equals the carrier frequency and how the output become zero.

ericgibbs · Jan 7, 2009

transistor495 said:
Eric,
I didn't understand a single word u told. Please give me a detailed explanation.
When the input equals the carrier frequency and how the output become zero.

hi,
Did you read the link I posted in my edit.

transistor495 · Jan 7, 2009

OK. That seems like a good link. I'll look on to that.
Do you think frequency modulation is possible below 2MHz?

ericgibbs · Jan 7, 2009

transistor495 said:
OK. That seems like a good link. I'll look on to that.
Do you think frequency modulation is possible below 2MHz?

hi,
What are you modulating the FM carrier with,? audio, data etc..

audioguru · Jan 7, 2009

Infrared headphones and speakers have the infrared FM modulated at 100kHz for one channel and at 200kHz for the other channel. Many of them use a CD4046 Phase-locked-loop IC to create the FM and to demodulate it.

transistor495 · Jan 7, 2009

Hi Eric,
I'm going to design a discrete fm detector circuit.
With minimum circuitry but acceptable performance.
For that I want to get a clear picture of the working principle of the available detectors.

It's on fm broadcast communication range only for audio.

I wonder there's no any clear information is available on net regarding the fm demodulation!

audioguru · Jan 7, 2009

The internet shows many FM demodulator circuits. Enter it in Google.
Don't you know about the Google search engine?

transistor495 · Jan 7, 2009

audioguru said:
The internet shows many FM demodulator circuits. Enter it in Google.
Don't you know about the Google search engine?

Yes!
Lot of patent info is coming
Using the patent they've designed IC's and the technology is welldone

Guruji,
Please explain a highly detailed view of this thing:
**broken link removed**
What is happening on each section and what is the input of the transformer etc

FM: Foster-Seeley discriminator

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