The modulator-transmitter is used to connect a VCR or camcorder to a TV via a high frequency.
In most VCRs output at high frequency, but in some models of VCRs and televisions intermediate frequency sound does not correspond to our standard (6.5 MHz), so when you connect with high frequency in the TV has no sound.
Most modulators operates in the UHF range, which requires ACS unit in the TV. The modulator-transmitter forms a complete television signal at a frequency of 1...3 channels MB. The intermediate frequency is set by potentiometer R6. The modulator can be connected to the shielded cable TV or over the air (like a game console such as the "Dandy")
On the VT3 transistor is assembled generator carrier frequency image, and the transistors VT1, VT2 - generator carrier frequency of the sound. On the VT3 transistor converts the low-frequency video and audio signals into radio frequency signals. Coil L1 - frameless, wound on a mandrel with a diameter of 6 mm wire of PEL 0.8 and contains 8 turns. L2 - 2 turns of wire PEL of 0.4 over L1. Potentiometer R6 is set to the desired intermediate frequency. Modulator transmitter can also be used in conjunction with a personal computer.
Author: N. Martynyuk; Publication: N. Bolshakov, rf.atnn.ru