Vhf-transmitter | Electronic Project Circuits

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VHF Test Transmitter

If you want to be independent of the local radio stations for testing VHF receivers, you need a frequency-modulated oscillator that covers the range of 89.5 to 108 MHz â€” but building such an oscillator using discrete components is not that easy. Maxim now has available a series of five integrated oscillator building blocks in the MAX260x series (see the May 2001 issue of Elektor Electronics), which cover the frequency range between 45 and 650 MHz. The only other thing you need is a suitable external coil, dimensioned for the midrange frequency.
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VHF Audio Video Transmitter by BF494

The circuit presented here is a simple audio/video transmitter with a range of 3 to 5 metres. The A/V signal source for the circuit may be a VCR, a satellite receiver or a video game etc. A mixer which also operates as an oscillator at VHF (H) channel 5 TV frequency is amplitude modulated by video signal and mixed with frequency mo enna, contains video carrier frequency of 175.25 Mhz and audio carrier frequency of 180.75 Mhz. Then, the transmitter is a B-System of CCIR compatible.

The circuit consists of transistor Q1 with its resonant tuned tank circuit formed by inductor L1 and trimmer capacitor VC1, oscillating at VHF (H) channel 5 frequency. Transistor Q2 with its tuned circuit formed using SIF coil and inbuilt capacitor forms oscillator. The audio signal applied at the input to Q2 results into frequency modulation of 5.5 Mhz oscillator signal. The output of 5.5 Mhz FM stage is coupled to the mixer stage through capacitor C8 while the video signal is coupled to the emitter of Q1 via capacitor C4 and variable resistor Inductor L1 can be wound on a 3mm core using 24SWG enamelled wire by just giving 4 turns. Calibration/adjustment of the circuit is also not very difficult. After providing 12V DC power supply to the circuit and tuning your TV set for VHF (H) channel 5 reception, tune trimmer VC1.

Read More Source: http://www.newcircuits.com/circuit.php?id=rfr003
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Be the first to comment - What do you think? Posted by admin - November 18, 2007 at 12:15 am

Categories: RF-Radio Frequency Tags: BF494, vhf-transmitter, Video Amplifier circuit

VHF Video Transmitter by 2N3904

This circuit is a powerful video sender in VHF band. The modulator section is designed to operate on either channels 7 to 13 or 14 to 29. For channels 7 to 13, L1 and L2 are 3 turns of #22 wire wound on a 3/16 inch form. For channels 14 to 29, L1 and L2 are 2 turns of #22 wire wound on a 3/16 inch form. Video signal is modulated as AM.

Source:http://www.newcircuits.com/circuit.php?id=rfr007
Thank you