The human species seems to be unique from all other living things in that it is the only one that desires to hold on to evidence or memories of the past. No other living thing on this planet purposely keeps a record of what has already occurred. What we are going to explore here is only one of the ways mankind has developed to record his past. There is evidence of human record keeping everywhere, from cave paintings, to hieroglyphs, to movable type. Recording sound and moving images are very recent developments. Part of the industrial revolution.
One of the earliest ways to record sound was by using a rotating wax cylinder, and a needle for making a grove in it. Soon came wire recorders like the one shown on the left in the above photo. The principles involved in wire recording have a lot in common with video recording. In the wire process a supply spool of wire rich in iron is passed across a recording head (an electromagnet ) to be magnetized by an incoming signal from a microphone or some other source. This causes the microscopic iron particles in the wire to acquire a variable magnetic charge that is unique to the signal being introduced. Once the recording has been made the wire can then be rewound and passed back over the head to reverse the process for playback. But this time the the recording head is passive and the stored magnetic charge on the wire produces a field of current that can be amplified and made to produce a sound closely resembling the one recorded earlier. The system works because the signal is converted when recorded so it can be stored on the wire and then converted again back when played back. And it can be played back again and again. The conversion process is what makes it all work. Not to sound corny but just shouting at the wire would accomplish nothing. This conversion process is used time and time again in the world of electronics. One the right in the above photo is a recorder similar to the wire unit but it uses audio tape. Here the iron particles have been ground up to a micro fine powder and then glued to a thin plastic strip. Tape came after wire because the technology had to wait for the development of acetate film, and then later, polyester film. So wire disappeared and tape took it's place. Keeping in mind the key factors of the materials need (the media) and the necessary conversion (converting process) let's take a look at recording or making an archive of a television signal. Click on the photo.
What you see here are several devices that use photographic film. (I'm going to assume you're familiar with the photographic process and I will not explain it here.) The large item on the left is a Kinescope or telecine machine. The device in the upper right is similar. They were used in the days before television was recorded on video tape. It was a relatively simple process. As you can see from the photos a motion picture camera was pointed at a small TV screen and what appeared on the tube was photographed as a movie. The results were grainy, flickered a lot and were in black and white (no color back in these days). The TV picture was simply being converted to film, and much of it survives today. During these times the only other recording methods that could of be used would of been vinyl records or wire. However, the signal requirements to record even a B&W picture was just too large for these to be practical. Magnetic recording of TV would have to wait for a dependable thin tape to be developed.
In the lower right in the above photo is a machine that turned the process of kinescope around. Here a projector sent an image from a motion picture film into a television camera, which allowed it to broadcast over television (or placed on tape, DVD or any other of a dozen chosen media). This is the just reverse of the other device and it is still being used today. Click on the photo again and here we the first broadcast video tape recorder. Certainly not suitable for the home it was the quadruplex system. As you can see it used very large reels because the tape was wide and traveled rather quickly through the machine. (Because lot's of information is required to record and play back a television picture.) Look in the upper left corner and a diagram shows that the unit had spinning heads (called the scanner) that turned at a ninety degree angle across a two inch wide magnetic tape. The quality of recording tape during these early times wasn't as good as it is today so it had to be wide and it had to travel through the machine at a fairly high speed, but it was good enough for network broadcasts, and recordings could be in color. Several drawbacks to this system are obvious. For remote recording you had to have a special truck for the massive amount of equipment needed. Also to send tapes back and forth require big cans, similar to movie theater film cans. The quadruplex was used for quite a few years until the introduction of a new, much handier process came along, and we are going to look at it next. Click on the photo once more.
As time passed magnetic tape improved. The micro fine iron grinding process was developed and the particles were being made a lot smaller so they could accept a stronger signal in a smaller space. Equipment manufacturers developed machines to take advantage of it. (Eventually chromium dioxide was developed and became the strongest particle for recording.) The rewards for these constant improvements were huge. There were a lot of television stations, businesses, etc. that wanted to take advantage of an easier for recording video. Even more impressive was the vast audience of television viewers that was growing at very rapid rate. The television station that could provide the best recordings and the fastest service was in a better position to ask for a higher advertising dollar (think news gathering). Click on the picture.
Sony was one company that developed a improved, smaller reel-to-reel video recorder that used a "helical" scanning drum. Helical simply means that the tape traveled around a video drum and the video heads rotated across the tape at a long angle (not in a 90 degree angle as with quadruplex). The extended recording swipe allowed for a less wider tape to be used that could hold a lot of information traveling at a slower tape speed. Ideal for mobile television. Sony also was ahead of the competition by having snapped early to the value of the transistor just developed by bell labs. With it they could make their units smaller, more portable and they could be very cost effective.
Next we look at just how Sony, along with others, changed video recording as we continue our discussion with the