decoding a 10khz tone!

[Qasim1]

i want to decode a signal of 10khz send on a 88 Mhz(FM Carrier wave) but i cant find any frequency counter to count for me the coming frequency that gets the anlog input and gives digital output.Can Anybody suggest me any idea for this?
I will be Much Greatful.

 

[audioguru2]

Qasim,
Why is there a 10KHz tone on an FM station? ???
Listeners with good ears and good speakers would complain, and it would be very hard on their tweeters.
There is a 19KHz tone, which is the stereo pilot tone, which can be measured if you filter it from the lower frequency audio and upper frequency stereo sidebands. So you need a bandpass filter at 19KHz.
Most modern stereo decoders use a phase-locked-loop to extract the 19KHz tone, and lock onto it. You can connect a frequency counter there. ;D

 

[shekhar_dandya]

U could use an IC 567 which is a tone decoder. It consists of a PLL , a comparator and a transistor switch, all integrated inside it.for more info about it search LM 567 datasheet

 

[audioguru2]

National discontinued their LM567 more than 8 years ago.
I think that Philips (the inventer) is still making their NE567.

 

[Qasim1]

actually i am making a tracking system in which each person is assigned a different tone say 10khz.12khz,14khz etc,but the carrier frequency should reamin same.In this case any frequency counter accepts a digital input and there is no one that has an analog one so is there any other way of doing this.I will recongnise the persons by their tone frequency.

 

[audioguru2]

Qasim,
If each person has a carrier frequency transmitter that is nearly the same, what is to prevent your receiver from picking-up interference between them? Your receiver will produce an interference beat frequency until it captures the strongest one.
Also, FM receivers do not "mix" the audio (your persons' tones) of transmitters that have nearly the same carrier frequency. The specification called "capture ratio" determines how little the amplitude of each received carrier must change before the receiver "captures" the strongest carrier, rejecting any others.

So you are going to need a separate transmitter/receiver for each person to be tracked.

 

[Qasim1]

No!You didn't understand my point.Basically i am doing this.

I am going to make a Tracking system in which a person will pass through a walkthrough gate with a transmitter card.The card is having no power supply and i am using here the concept of crystal radio.The Walkthrough gate is having a high power transmitter and the card carried by the person is going to get its required power by that transmitter.Now one person is passing at the time.Each person is assigned a different tone at the same frequency as in case of mobile phones.Can u suggest any thing about this!

 

[audioguru2]

Qasim,
OK, now you have only one person at a time, so it should work.
Any frequency counter will take the analog tone from your FM receiver and display the exact tone frequency. But instead of having a big long number displayed, maybe it is best to just light an LED for the ID of each person. In that case, an NE567 circuit that is tuned to each person's tone frequency is required.
Note that if you are using a standard FM receiver, its de-emphasis rolls off the high frequencies above 2100Hz or 3200Hz, depending on your country's system, at 6dB per octave. Also, the receiver's audio response may have a 19KHz notch, which sharply attenuates frequencies at about 15KHz and up.
I hope that your high power transmitter doesn't cause problems with electronic medical devices such as pacemakers, etc.

 

[Qasim1]

Thanks a lot.I purchased the ic ne567 and its cheap.Thanx a lot for ur assistance.I am recieving the output at controller 8051 input port and then passing it to the serial port.

Thats really the coolest point of electronics related problems on internet.

Thanx alot ELECTRONICS-LAB.
Qasim