By Rudolf F. Graf
Rudolf Graf and William Sheets have written a booklet containing twenty low-power (LP) transmitter initiatives, ideal for the electronics hobbyist and radio experimenter. Now that the FCC has replaced its laws approximately «pirate» transmissions, increasingly more everyone is constructing radio and video stations for broadcast from their houses. construct your personal Low-Power Transmitters addresses functions for hobbyist broadcasting of AM, SSB, television, FM Stereo and NBFM VHF-UHF signs with apparatus the reader can construct himself for hundreds of thousands of greenbacks under related gear offered at the retail market.
The authors additionally totally discover the criminal limits and ramifications of utilizing the gear in addition to tips on how to get the easiest functionality for max diversity. the main virtue is referencing a reasonably cheap resource for all wanted elements, together with the broadcast circuit board, in addition to the kit.
Projects within the booklet comprise: LP FM stereo transmitter digitally synthesized PLL FM stereo transmitter LP AM transmitter for 150-1710 KHz radio regulate transmitter/receiver service present transmitter and AM and FM receivers LP VHF one-way and two-way audio hyperlinks 1-watt 40-meter CW transmitter for ham radio use SSB LP transmitter for 10-meter ham radio use 2-meter VHF FM ham radio transmitter FM video hyperlink for 900 MHz NTSC/PAL operation 2-watt television transmitters for 440, 900 and 1300 MHz novice television NTSC/PAL transmissions linear amplifier for 440MHz, 10-15watt NTSC/PAL operation Downconverters for 440, 900 and 1300 MHz with VHF channel three or four output television video receiving structures and AM-FM IF structures LP video hyperlink for UHF channels 14-18 1-watt CW transmitter for half 15 LF radio experimentation CW identifier for transmitters try apparatus initiatives for LP transmitters in addition to an RF strength meter and modulation video display.
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Additional resources for Build Your Own Low-Power Transmitters Projects for the Electronics Experimenter
R2 biases Q1 and R6 set the bias on Q2. C1 couples mike audio to the ampliﬁer stage. C3 prevents degenerative (negative) feedback through R11 by bypassing any signals at the emitter of Q2. Audio is coupled to the modulated oscillator via C2 and R7. R4 is a gain control and is used to set the optimum value of gain for the application. The oscillator portion is identical to that of the wireless mike, so we do not discuss it in detail. Note that it is fed DC from a resistor and zener diode regulator, R10 and D1, to supply a constant 9 volts to the oscillator.
Cards with wideband receivers covering 500 kHz to 1300 MHz are available for installation in your PC and contain a synthesizer chip similar to the ones previously mentioned. A PLL chip may also be set up to act as a frequency multiplier, enabling elimination of a discrete transistor multiplier chain. The Motorola MC13176 one-chip transmitter does just this, and allows a crystal at 1/32nd of the desired output frequency to control a VCO operating in the VHF or UHF band. 75 MHz, add a few components, and get a few milliwatts at 440 MHz.
In practice, R18 is adjusted so that this occurs at 85–90 percent modulation. Although this scheme does not prevent negative clipping or deliberate overmodulation, it works well for normal application with speech or music. The PLL synthesizer section uses an MC145151-2 LSI chip. This chip contains a reference oscillator, reference divider, charge pump phase detector, and variable divider that can be programmed for divide ratios of 3 to 16383. The reference divider is programmable, by hardwiring pins, at various ﬁxed ratios that are mostly powers of two.