WIRELESS_FM_CODE_PRACTICE_TRANSMITTER

Published:2009/7/12 20:45:00 Author:May | From:SeekIC

The circuit shown is a low-power, tone-modulated FM transmitter that can be used with any FM broadcast receiver for code practice. Transistor Q1 and its associated components make up a phaseshift audio-frequency generator circuit. Potentiometer R11 sets the tone frequency. Transistor Q2 is connected in a high-frequency RE oscillator circuit that operates in the FM broadcast band. Potentiometer R12 sets the modulation level. Transistor Q3 operates as a switch, turning on the FM transmitter each time the CW key is closed. Coil L1 is a homemade air-wound coil. Take a 6 1/2-in length of 20-gauge enamel-covered wire and close-wind it around a 1/4-in-diameter form; leave about 1/4 in free at each end. Remove the insulation from the ends and slide the coil off the form. The overall length of the finished coil should be about 1/4 in. Set R11 and R12 to midposition and close the CW key. Then set your FM receiver to a clear spot on the low end of the dial and slowly adjust C8. Once the tone is heard, R11 can be set for the desired tone frequency and the tone level set by R12. If your oscillator won't tune to the top end of the band, carefully stretch the windings of L1 and retune. The circuit's operating range can be increased by adding a very short antenna to the emitter of Q2.



Reprinted Url Of This Article:
http://www.seekic.com/circuit_diagram/Communication_Circuit/WIRELESS_FM_CODE_PRACTICE_TRANSMITTER.html

Print this Page | Comments | Reading(3)