The audio is applied via input connector, J1. This can be a phono type, note also that audio must be mono, if a stereo input is used, either use a stereo to mono adapter, or one channel only. Transistor Q1 acts as an oscillator and amplifier, the primary of T1 and its internal capacitor oscillating at 5.5Mhz, the transistor itself provides audio gain. Some adjustable of frequency may be obtained by moving the core of T1. T1 should be a 5.5MHz IFT, available from an old TV or FM radio or available in UK from Jabdog, see link below:http://www.jabdog.com/toko-10k.htm
The modulated, audio signal, is now passed to Q2, which acts as a modulation and generates the carrier frequency for the transmitter. C5 and inductor L1 form the tank circuit which oscillate at the carrier frequency. Once trasmitting adjustment of C5, will alter the channel of the transmitted signal.
The video signal is fed via input jack J2. The video signal must be composite, e.g. just video and not contain any audio. Suitable inputs from cameras, or video cameras should be ok. Preset R7 allows adjustment of the video signal input, and hence also controls modulation level. Q2 mixes the video input with the sound input to produce a modulated RF video signal containing both audio and video components.
Because this transmitter is working at 54to 216MHz then a short length of wire or telescopic whip antenna will work. Transmitting at higher frequencies, e.g. 546Mhz to 860Mhz requires a different RF transistor and a portable TV antenna to transmit at these frequencies.For more information on TV systems visit the links below:
|Circuit Exchange International||Return to Radio Circuits||http://www.zen22142.zen.co.uk|