Videocassette recorder

VCR (abbreviated VCR Video Cassette Recorder from English ) are devices for recording and playback of audio and video signals (typically television images ). Initially devices with magnetizable bands ( MAZ, video cassettes ) were thus always meant, now stands in the German is used (unlike in English ) also increasingly on devices, the data disks ( DVD) or hard disk drives ( HDD) use.

Technology

Mechanics

Mechanical recording

Already in the early days of television hobbyists tried to record the broadcasts. This was achieved with the help of some modified records. The low bandwidth it took for the former mechanical television, was able to be recorded. Some images used even more narrowband formats, such as 30 lines at 4 frames per second.

In the 1970s, the Telefunken company launched a new test of mechanical recording, see image plate.

Magnetic recording

With the advent of wire tape recorders and devices, attempts have been made to record television images on magnetic tapes.

Electronics

Modulation method

Magnetic records are often very frequenzunlinear (not constant). High frequencies are more strongly represented than low. This must be compensated by suitable electronic circuits. Of course, this only works up to a certain ratio between the highest and lowest frequency. For tapes, this ratio is about 1:1000. However, frequencies of a few Hertz to be transferred to several megahertz in the video area. This corresponds to a ratio of approximately 1:10,000,000, too much for the direct recording.

Color recording

Color television was still new, when the first VCRs came on the market. Therefore, the color was once ignored.

VHS, S -VHS, VHS -C: 627 kHz
Video 2000: 625 kHz
Video 8: 743 kHz

Sound recording

Timecode method

For cutting tapes, it makes sense to each image individually labeled with a number in order to find it again.

Digital Systems

Digital video tape recorder systems use different methods to encode video and audio signals. If the signal is sampled, for example, with 4 times the color subcarrier frequency in the pulse code modulation ( PCM), as one speaks of the " composite " method. However, the signal is often divided prior to the encoding in the color difference signals or RGB. Thereafter, as a rule, these signals are processed as PCM signals.

Originally, the PCM signals are recorded without data compression. This resulted in a good quality, but required high recording speeds and the handling of large amounts of data. Later, computers were so powerful that data compression and decompression in real time was possible. This has made it possible for the data rates and volumes to reduce almost no concessions to quality by a factor of 1:2 to 1:100, as the redundant recording of several omitted to little more distinctive pictures from a film and plain surfaces not stored with the full resolution must be.

The digital tape recorder systems are currently displaced by hard disk recorder and digital audio recorder with hard memory, since the acquisition and maintenance costs are lower than for tape devices. The hard disk recording, but especially the solid state recording is also characterized by low access times and low wear.

Home video recorder

The first VCR for home use came the early 1960s on the market. An example of an early device was the Loewe Optacord 500, which was presented at the Radio Exhibition in 1961 to the public. Among the most prominent owners of these early, then still as good as unknown for the home consumer video recorders, were from about 1965, the musician John Lennon and Paul McCartney, who kept their devices not yet entered series production prototype of a still officially in development technology.

In the 1970s, the VCR ( with offshoots VCR Long Play and SVR ) and formats Video 2000 from Philips and Grundig have been developed in Europe. However, this European formats could be difficult to enforce in the United States and Japan.

The European developments were soon beset by two Japanese systems: Sony Betamax and VHS from JVC. The first player to the VHS recording format was the HR 3300 by JVC, the autumn was introduced in 1977.

Although Betamax over VHS offered a minimally better image quality and better tape drive properties, but failed because the licensor Sony from other manufacturers took donations for the production of Betamax machines. By the end of the 1980s, VHS had supplanted mainly due to a more skilful licensing policy the competing systems completely out of the retail business. This ultimately won by VHS battle for market share has been known as a format war. He repeated in similar form from about 2005 as a competition between HD DVD formats, VMD and Blu -ray disc, all of which were developed as a successor to DVD which was won by Blu -ray.

Further, even professional formats, can be found in the article video format.

In the Federal Republic of Germany in 1979 about 270 000 units were sold. In 1981 there were already about 750 000 to 1.4 million in 1983. 1985 stood at about seven million homes a video device and thus in every fourth household.

The introduction of the DVD as playback and since 2000 increasingly as a recording medium for home urges tape-based video devices increasingly slower. However, because many users want to continue using their analog recordings, there are still buying VHS recorder. Some of these devices combine the different recording techniques (usually a VHS drive and a DVD recorder in one unit) and thus offer an easy way to copy from one format to another.

Description of a VHS drive

The video recorder drive ( the picture shows a VHS drive ) has the task to record the video cassette to feed them to thread the tape and transport. This high precision is necessary. This concerns in particular the tracking of the belt ( tracking ) and the tape transport by the so-called band servo (servo motor which drives the capstan ) and the head drum motor ( head drum servo) which drives the top plate with the video heads. The rotational speeds of all the servo motors are controlled by a microcontroller.

Figure VCR drive from above:

2 heads: two video heads for standard play or combined for Standard Play and Long Play with mono- longitudinal track - tone
4 heads: two video heads for standard play or combined for standard play and long-play and two rotating heads for audio hi-fi stereo sound. When editing this only in mono
6 heads: four video heads for standard and long play, and better still image and two audio heads for hi-fi stereo; standing erase head, so dubbing only in mono.
7 heads: four video heads for standard and long play, two audio heads for Hi -Fi stereo and a rotary erase head, better for video editing plus "standing" erase head, audio dubbing in Mono

3: The shaft motor has the task to collect the tape and the tape ( by means of various "fingers" and additional mechanics) extract from the cassette, and to wrap around the rotating drum. In addition, he takes over the control between the operating modes of the VCR (play, fast forward, rewind, etc.). For this purpose, the so-called mod - switch is.
4: The erase head will erase all information on the tape when recording new.
5: pinch roller transports the tape as well as in tape recorders, by pushing it against the shaft.
6: The tape head records the mono sound and plays it. Built-in, the synchronization header (also called CTL head). It is used for recording synchronization pulses, and thereby control the current rotational angle of the wheel head relative to the tape advancing in the reproduction. In addition to the sound and CTL head is the erase head for the mono track (black), which is required for dubbing and video editing.
7: The so-called capstan ( capstan, with tape recorders, also called sound wave ) is driven by a servo band (not seen here). It transports the tape. After threading of the strip, the pinch roller presses the tape against the capstan so that it can drive the belt.
8: IR sensor for detecting whether a cartridge is inserted. 18 is the corresponding transmitter.
9 and 10: The deflection rollers place the tape around the head drum. They are height adjustable to adjust the tracking. The band is placed around the drum head that it covered about half the drum circumference. From above the belt runs in the form of "M", so the method is also called M -loading.
11: The unwinding takes on a reel of video tape. During rewinding it is driven by the servo band.
12: The winding spindle picks up the second reel of videotape. During playback of the tape and the mandrel during forward travel and the servo band ( capstan ) is driven.
13: guide grooves of the cassette holder.
14: A guide pins of the cassette holder.
15: This plastic nose unlocks the cassette lid that protects the tape.
16: This lever pushes the 15 forward to release the cartridge door when you insert the cassette. If the cartridge moves down this lever opens the cartridge door.
17 the cassette holder accommodates the tape.
18: IR sensor for detecting whether a cartridge is inserted. It is mounted on a plastic pen. This plastic pen unlocks the reels of video tape.
19: Depending on the rotational direction of the band servos this lever toggles between On or unwinding.

Figure VCR drive from below:

Quadruplex videotape Bandwidth (signal processing) Still video camera Floppy disk Amplitude modulation S-VHS YUV Charge-coupled Device D9 Film frame Non-volatile memory Video Cassette Recording Videotape format war Servomotor Clockwise

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