walkie talkie
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prajiv
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Posts: 1
Joined: Dec 2009
#1
18-12-2009, 11:09 AM


has anyone woked on walkie talkie or fm transmitter+fm reciever both.pls provide me its report if anyone of u have got it.pls send it at
heatred17@yahoo.com
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ajukrishnan
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Posts: 213
Joined: Dec 2009
#2
18-12-2009, 02:05 PM

Walkie talkie
FM transmitter
The variable capacitor inductor will vibrate at frequencies in the FM radio band (88 to 108 MHz). The electric microphone picks up the sound signals and converts it to electric signals. This microphone is battery powered and according to the V=IR Ohm's Law, changes in resistance for fixed voltage will result in proportional changes in current. This current feeds into the base of the 2N2222 NPN transistor which is connected the variable capacitor, inductor and antenna. depending on your variable capacitor's value, your voice will be modulated to transmit at a frequency between 88 and 108 MHz. If a nearby pocket FM radio is tuned to this frequency, your voice can be picked up by it.
Visit this site for ideas on building one:
boondogtutorials/rfTransmitter/rfTransmitter.htm

FM reciever
Regenerative radio reciever
They are simple detectors which may be used for common wave or single side band when adjusted for oscillation or a-m phone when set just below point of oscillation. It consists consists of three sections: a radio frequency RF stage, a detector stage, and an audio amplifier stage. A bipolar transistor is used in the RF stage, a JFET in the detector and a low-cost IC in the audio amplifier stage. The RF stage transistor amplifies the antenna signals and provides isolation to prevent the radio's oscillations. JFET acts as a "regenerative" detector, which, by the use of positive feedback, greatly increases the receiver's sensitivity. And also provides reference oscillations for CW and SSB signals. The audio stage amplifies the audio signal and provides enough output power to drive speaker or headphones.

A detailed circuit diagram can be found at:
electronics-tutorialsreceivers/regen-radio-receiver.htm
.

.pdf   Wireless-FM-Transmitter.pdf (Size: 310.54 KB / Downloads: 120)
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