Description
A very simple TV audio video transmitter circuit can be constructed using this schematic diagram . This TV audio video transmitter circuit can be used to transmit video signals from VCR ( or some other device ) to a TV without using any cable .
Video signals input at jack J1 are first terminated by resistor R6 and coupled through capacitor C1 to clamping-diode D1. Potentiometer R3 is used to set the gain of the video signal; its effect is similar to that of the contrast control on a TV set.
Bias-control R7 can be used to adjust the black level of the picture so that some level of signal is transmitted, even for a totally dark picture.
RF-transformer T1 and its internal capacitor form the tank circuit of a Hartley oscillator that's tuned to 4.5 megahertz. Audio signals input at J2 are coupled to the base of Q3 via C2 and R4: the audio signal modulates the base signal of Q3 to form an audio subcarrier that‚s 4.5-megahertz higher than the video-carrier frequency.
Video signals input at jack J1 are first terminated by resistor R6 and coupled through capacitor C1 to clamping-diode D1. Potentiometer R3 is used to set the gain of the video signal; its effect is similar to that of the contrast control on a TV set.
Bias-control R7 can be used to adjust the black level of the picture so that some level of signal is transmitted, even for a totally dark picture.
RF-transformer T1 and its internal capacitor form the tank circuit of a Hartley oscillator that's tuned to 4.5 megahertz. Audio signals input at J2 are coupled to the base of Q3 via C2 and R4: the audio signal modulates the base signal of Q3 to form an audio subcarrier that‚s 4.5-megahertz higher than the video-carrier frequency.
The FM modulated subcarrier is applied to the modulator section through C5 and R9.
Resistor R9 adjusts the level of the subcarrier with respect to the video signal.
Transistors Q1 and Q2 amplitude modulate the video and audio signals onto an RF-carrier signal. The operating frequency is set by coil L4, which is 3.5 turns of 24- gauge enameled wire on a form containing a standard ferrite slug.
Resistor R9 adjusts the level of the subcarrier with respect to the video signal.
Transistors Q1 and Q2 amplitude modulate the video and audio signals onto an RF-carrier signal. The operating frequency is set by coil L4, which is 3.5 turns of 24- gauge enameled wire on a form containing a standard ferrite slug.
Circuit Diagram
Resistor R12 is optional; it is added to help match the output signal to any kind of antenna.
To align this audio video transmitter you need to tune a TV receiver to an unused channel between 2 and 6. The TV must have an indoor antenna connected directly to it; an outdoor antenna or cable won't work. Make sure both potentiometers (R3, R7) are in middle position and apply power to the transmitter. Adjust L4 with a nonmetallic tool until the TV screen goes blank ,then fine-adjust L4 for the "most-blank" picture.
Connect the video and audio outputs from a VCR(AV source) to jacks J1 and J2 (respectively) of the transmitter .
After that you should see a picture on the TV screen: if you do, readjust L4 for the best picture; if you don't, check the board for any bad connections. Next, adjust R3 for the best picture brightness and R7 for the best overall picture.
Finally, adjust T1 with a nonmetallic tool for the best sound .
The TV transmitter combines line level audio and video signals, and transmits the resulting signal up to 300 feet. The circuit can be powered from a 9-12V power supply circuit .
Source - http://www.electroniq.net/radio-frequency/tv-audio-video-transmitter.html
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