Carrier-current-audio-transmitter
The choice between AM, narrowband FM (less than 15 kHz), or wideband FM (greater than 30 kHz) is determined by the specific application. FM is preferable for music transmission due to its superior noise immunity. For speech or other non-critical applications, AM may suffice. The transmitter allows for either mode to be selected via a switch. Audio is input from source S1 to either the FM or AM circuitry. In the FM section, amplifier Q1 receives an audio signal in the range of 10 Hz to 20 kHz with an approximate amplitude of 0.5 V peak-to-peak. The audio gain is adjustable through resistor R5, allowing for up to 60 kHz deviation from the voltage-controlled oscillator IC1, which is nominally set to 280 kHz. Both IC1 and Q1 are powered by a regulated 12 V supply from IC2.
A square-wave signal from pin 3 of IC1 drives transistor Q2, which in turn drives the output amplifier Q3. A coupling network is implemented to match the nominal 45-ohm output impedance of Q3 to the 10-ohm AC line impedance. In AM mode, audio is coupled to transistor Q8 through resistor R24, followed by amplification through transistors Q4 to Q7. The normally stable DC voltage at test point A is modulated at an audio rate. Since Q2 and Q3 derive their DC Vcc from test point A, the VCO carrier input to Q2 is amplitude modulated by the varying Vee amplitude, resulting in an amplitude-modulated output from the transmitter. Proper adjustment of carrier level resistor R23 and audio level resistor R24 allows for modulation up to 100%. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804.
The transmitter circuit is designed to accommodate both AM and FM modes, catering to diverse audio transmission requirements. The FM section begins with an audio input received by Q1, which is configured to amplify signals within the specified frequency range. The adjustable gain via R5 is critical for ensuring the output signal meets the necessary deviation for effective FM transmission. IC1, functioning as a voltage-controlled oscillator, generates a carrier frequency that is modulated by the audio signal processed through Q1.
The output stage, driven by Q2 and Q3, is optimized for impedance matching to ensure efficient power transfer to the antenna or load. The coupling network plays a vital role in maintaining the integrity of the signal and minimizing reflections that could lead to signal degradation.
In AM mode, the circuit takes a different approach. The audio signal is routed through R24 to Q8, where it is amplified before being passed through a series of transistors (Q4 to Q7) that modulate the carrier signal. This process allows for the amplitude of the carrier wave to vary in accordance with the audio input, achieving the desired modulation depth.
The careful design of the modulation controls (R23 and R24) ensures that the transmitter can achieve high modulation percentages, which is essential for maintaining audio fidelity during transmission. The availability of the kit from North Country Radio provides an accessible option for enthusiasts and professionals looking to implement this versatile transmitter in various applications.The decision to use either AM, narrowband FM Oess than 15kHz), or wideband FM (greater than 30 kHz) depends on the application. For the transmission of music, FM is better because it has greater noise immunity. For speech or other noncritical applications, AM may be satisfactory. Our transmitter permits either mode by switch selection. Audio is fed from Sla to either the FM or AM circuitry. Starting with the FM section, amplifier Q1 accepts an audio signal in the 10 Hz to 20 kHz range of about 0.5 V peak-to-peak.
The audio gain is adjusted via R5 to provide up to 60 kHz deviation of voltage-controlled oscillator I C 1 which is set to nominally 280kHz. IC1 and Q1 are supplied with a regulated 12 V from IC2. A square-wave signal from IC1 pin 3 drives Q2, and Q2 drives the output amplifier Q3. A coupling network is used to match the nominal 45-0 output impedance of Q3 to the 10-0 ac line impedance. In the AM mode, audio is coupled to Q8 via R24 and then amplified again by transistors Q4 to Q7. The normally stable de voltage at test point A is thereby varied at an audio rate. Because Q2 and Q3 obtain their de Vcc from test point A, the VCO carrier input to Q2 is amplitude modulated by the varying Vee amplitude.
That~produces an amplitude-modulated output from the transmitter. Careful setting of carrier level R23 and audio level R24 provides up to 100% modulation. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804. 🔗 External reference
A square-wave signal from pin 3 of IC1 drives transistor Q2, which in turn drives the output amplifier Q3. A coupling network is implemented to match the nominal 45-ohm output impedance of Q3 to the 10-ohm AC line impedance. In AM mode, audio is coupled to transistor Q8 through resistor R24, followed by amplification through transistors Q4 to Q7. The normally stable DC voltage at test point A is modulated at an audio rate. Since Q2 and Q3 derive their DC Vcc from test point A, the VCO carrier input to Q2 is amplitude modulated by the varying Vee amplitude, resulting in an amplitude-modulated output from the transmitter. Proper adjustment of carrier level resistor R23 and audio level resistor R24 allows for modulation up to 100%. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804.
The transmitter circuit is designed to accommodate both AM and FM modes, catering to diverse audio transmission requirements. The FM section begins with an audio input received by Q1, which is configured to amplify signals within the specified frequency range. The adjustable gain via R5 is critical for ensuring the output signal meets the necessary deviation for effective FM transmission. IC1, functioning as a voltage-controlled oscillator, generates a carrier frequency that is modulated by the audio signal processed through Q1.
The output stage, driven by Q2 and Q3, is optimized for impedance matching to ensure efficient power transfer to the antenna or load. The coupling network plays a vital role in maintaining the integrity of the signal and minimizing reflections that could lead to signal degradation.
In AM mode, the circuit takes a different approach. The audio signal is routed through R24 to Q8, where it is amplified before being passed through a series of transistors (Q4 to Q7) that modulate the carrier signal. This process allows for the amplitude of the carrier wave to vary in accordance with the audio input, achieving the desired modulation depth.
The careful design of the modulation controls (R23 and R24) ensures that the transmitter can achieve high modulation percentages, which is essential for maintaining audio fidelity during transmission. The availability of the kit from North Country Radio provides an accessible option for enthusiasts and professionals looking to implement this versatile transmitter in various applications.The decision to use either AM, narrowband FM Oess than 15kHz), or wideband FM (greater than 30 kHz) depends on the application. For the transmission of music, FM is better because it has greater noise immunity. For speech or other noncritical applications, AM may be satisfactory. Our transmitter permits either mode by switch selection. Audio is fed from Sla to either the FM or AM circuitry. Starting with the FM section, amplifier Q1 accepts an audio signal in the 10 Hz to 20 kHz range of about 0.5 V peak-to-peak.
The audio gain is adjusted via R5 to provide up to 60 kHz deviation of voltage-controlled oscillator I C 1 which is set to nominally 280kHz. IC1 and Q1 are supplied with a regulated 12 V from IC2. A square-wave signal from IC1 pin 3 drives Q2, and Q2 drives the output amplifier Q3. A coupling network is used to match the nominal 45-0 output impedance of Q3 to the 10-0 ac line impedance. In the AM mode, audio is coupled to Q8 via R24 and then amplified again by transistors Q4 to Q7. The normally stable de voltage at test point A is thereby varied at an audio rate. Because Q2 and Q3 obtain their de Vcc from test point A, the VCO carrier input to Q2 is amplitude modulated by the varying Vee amplitude.
That~produces an amplitude-modulated output from the transmitter. Careful setting of carrier level R23 and audio level R24 provides up to 100% modulation. The kit is available from North Country Radio, P.O. Box 53, Wykagyl Station, NY 10804. 🔗 External reference