Ftg. 6. Modified transmitter; using a caroon microphone.

livity of each receiver unit. Since if might become necessary to perform field tests, interconnecting various pieces of bulky and heavy test equipment was an undesirable alternative

To meet the requirement, I designed, built, and tested the transistor circuit shown in Fig. 5. The 2N2222 CFrcuitry is a three-element phase-shift oscillator circuit, designed to yield a 1,000-Hz sine wave The 1,000-Hz sine wave ts then applied to the TCG-610 varactor diode (6 pF at 4 volts), which changes the tank capacitance, thus varying the rf oscillator frequency at a 1,000-Hz rate. The 1,000-Qhm potentiometer in the collector circuit may be adjusted to enable the desired frequency modulation level.

The Hartley rf oscillator, designed around a readily availabie MPF-102 JFE"I\ has an output that should be relatively stable if it is enclosed in a metal box (thus minimizing changes in tank capacitance). The completed transmitter has a range of 30 fee* when not enclosed (but without an, antenna) When enclosed, a BMC or F connector car be used to feed the rf to a small foop If you decide to build this unit, be careful, the FCC has regulations regarding the radiation of rf.

One of my colleagues. Bohdan Stryzak. modified the transmitter ay eliminating the sine-wave* oscillator portion and replaced Jt with a carbon microphone as shown in Fig. 6.This created for his children a three-dollar portable transmitter that could be used with any portable FM receiver as a handie-talkie,

William Rynonet PhD Annapolis MD


The AUTO-KaU Ak-io s a CTMF selective calling jnjt n connect to the externra! speaker jack on yo^ VHFvJHF FM transceiver scamef etc Yqi* Speaker rwra-ns silent untiI someone senes ycix personal 3-Cigrt Tfluc^-Tor?" code That means you [and the XYL1) don't have lo lisien to all Ttie chatter aJI the Ijme But fi someone wants to reach you the y tan G^eai for families with two or more hams, activation o\ emergency ne¡s etc

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