Basic Theory

BASIC THEORY

A VCR may seem like a complicated electronic marvel. If one were to study all that goes on inside electronically, it would be very impressive. But mechanically, it's really only a simple audio recorder with a few extra parts. Figure X.1 shows the transport of a simple audio cassette recorder. Starting on the left, notice it has a supply reel table with brakes, a record and playback head, a capstan, pinch roller and a take-up reel table with brakes. The real similarities are with the controls. An audio cassette recorder has PLAY, RECORD, STOP, FAST FORWARD, REWIND, PAUSE, EJECT and ON-OFF buttons. Just like on a VCR. Most also have a tape counter with reset button, some even have cue and review functions as well.

Figure X.2 shows the transport of a VCR. Note that most of the components are the same. The only major difference, besides the size of the cassette, is a tape tension regulator and a video drum with guide rollers to wrap the tape around it. You can think of the video drum as a video head.

The biggest problem with getting a picture to record on a regular audio deck is the tape speed that is required by video frequencies. It would have to travel at 400 feet per minute! A reel of tape one mile long would only last 12 minutes. Somewhere along the way, someone came up with a better idea. It was found that instead of moving the tape at 400 feet per minute, You could put the head on a spinning drum and move the head 400 feet per minute instead. As long as the head was tilted so it could record long diagonal tracks on the tape, it worked. The method was perfected when a tape tension regulator was invented along with electronics that could precisely spin the head and move the tape at accurate speeds. The rest was history.