A much better idea is to ensure that the HF signal containsa large number of different frequencies. Differentusers will want different channels, the carrier wave can become somewhatdifficult to locate, and unless the frequency is exactly spot on no signalwill be received. If this is only a singlechannel, as suggested above, h gives rise to some practical problems. A very important feature of the circuitthat must be decided is the transmission frequency. The frequencystability must be very good as, indeed, must the quality of the display.The required frequency stability is achieved by the use of a crystal oscillator.A well thought out choice of component values takes care of the displayquality: the modulator allows a resolution of 80 characters per line, asthis is a value that is often needed. The layoutThe whole business is not quite as simple as we have just suggested, ofcourse, as the mini transmitter must meet certain requirements. Then all that remains to do is tune the TV tothe correct frequency The oscillator is modulated with the video signaland the modulated carrier wave thus generated is fed into the TV set'saerial input via a cable. Whatdoes a modulator actually do? In general -and this design is no exceptionto the rule - it is a simple oscillator that generates a frequency somewherein the VHF or UHF region. It is a verysmall transmitter, admittedly, but none the less that is what it is. Then all that remains to do is tune the TV tothe correct frequency.Ī 'TV modulator' is really no more than a transmitter.

It is a simple circuit that processes video signals toenable them to be fed straight into the TV set's aerial input.Ī 'TV modulator' is really no more than a transmitter.

If theTV receiver in question does not have a video input and its owner is reluctantto vandalise it in order to fit one then this sort of modulator is theobvious solution. Computers, video games, video cameras, games computers all of theseproduce video signals that must be displayed via a television set.

Av rf converter circuit