The Video Cassette Recorder (VCR)

Introduction

The main purpose of the video recorder is recording and replaying video and audio signals. Although built-in tuners and timers have become integral parts of the average video recorder, they are not prerequisites for reaching the main goal: audio and video registration and playback.

In this chapter we will take a look inside the VCR, at the various video systems, and at the most common features of video recorders. We will also take a close look at the carrier of the video signal: the videotape.

How The VCR Works

The Helical Scan System

In an audio cassette deck, which only registers audio signals, the tape passes over a static recording/playback head at constant speed. The higher the speed of the tape, the more tape particles pass the head opening and the higher the frequencies that can be registered. Thanks to the extremely narrow head opening, it is possible to record and play back the entire tone range, up to 18,000 or 20,000 Hz, despite a slow tape speed of no more than 4.75 centimeters per second.

However, to register video signals, a range of 3.2 MHz is required and so a tape speed of approximately 5 meters per second is a prerequisite. This is over 100 times as fast as the tape speed for an audio cassette deck. The required high recording speed for video recorders is realized by the helical scan system without such high tape speeds. The system basically consists of a revolving head drum, that has a minimum of two video heads.

The head drum has a diameter of approximately 5 cm and rotates at a speed of 1500 revolutions per minute. The 1/2" (12.65 mm) wide videotape is guided around half the surface of this drum, in a slightly oblique manner. This is achieved by positioning the head drum at a slight angle. The tape guidance mechanism then ensures that the tape is guided through the device at a speed of approximately 2 cm per second (half of the low tape speed that is used in audio cassette decks).


Tape guidance along the head drum with the video heads writing tracks on the tape.

In the meantime, the rapidly revolving video heads write narrow tape tracks of no more than 0.020 to 0.050 mm wide on the tape, next to each other, diagonally. Every half revolution, each of the two heads writes one diagonal track which equals half an image. The first head writes one track, i.e., the first field (the odd numbered scanning lines). The second head writes a second track, i.e., the other half of the image (the second field: the even numbered scanning lines), which precisely fits in the first image. This corresponds to the interlacing principle, as applied in television (see Chapter 2: TV set). One full revolution of both heads results in two diagonal tracks right next to each other, together forming one entire image scan (a frame). This means that two apparently contradictory requirements can be realized simultaneously: low tape speed of only 2 cm per second and at the same time a high registration speed (relative tape speed) of no less than 5 meters per second. These two requirements make it possible to record the high video frequencies up to 3.2 MHz. At the same time, the low tape speed gives a time capacity up to three hours.

Azimuth Settings

Compared with early video recorders, modern day video recorders have their video tracks lying right next to each other. To avoid interference, the two video heads are angled slightly away from each other. As a result, the video head openings that transmit the magnetic tracks to the tape, create an angle between them. The heads are 15 degrees angled in opposite direction, making a total angle of 30 degrees.This diverted registration angle ensures no problems are caused if the heads slightly lose track when playing back and touch the next track. The heads only register tape information at an angle that precisely corresponds to the position of the head opening. This system is called the azimuth recording system. If the video heads stray too far from the track, which could lead to distorted images, tracking control can correct this.


Azimuth settings. The head openings are cut with different azimuth angles, so that the tracks can be written next to each other.

Synchronization Track

The revolutionary speed of the head drum and the video heads needs to maintain a constancy within strict parameters. Moreover, the tracks must be scanned during playback in precisely the same way as they were recorded. Each tape track is synchronized at the recording stage by means of field synchronization pulses. These pulses are generated in the video recorder by a separate head which are recorded on a separate narrow track at the side of the video tape. This is called the synchronization, servo or control track.


Position of the video, audio and synchronization tracks on the tape.


Position of the audio, sync and erase heads inside the VCR.

Video Systems

There are three major video systems in use today: 

     Video Home System (VHS)
     Betamax
     Video Hi8

When the video recorders were first introduced, Philips also developed a system called V2000. Despite the fact that is was a high quality system, it was not successful in the market. Although Betamax was reasonably successful at first, its popularity waned and VHS was adopted as the world standard.

Betamax
The Sony Betamax System, launched in 1975, was based on the pre-existing professional Sony U-matic-system. In the Betamax system, the video tape is guided along the head drum in a U-shape for all tape guidance functions, such as recording, playback and fast forward/backward. When the cassette is inserted, the tape is guided around the head drum (called threading). Threading the tape takes a few seconds, but once the tape is threaded, shifting from one tape function to another can be achieved rapidly and smoothly.


The Betamax U-system before (top) and after (bottom) threading.

VHS
JVC's VHS System was introduced one year after the launch of Betamax. In VHS, the tape is guided through in an M-shape; the so-called M-tape guidance system. It is considered simpler and more compact than the U-system. Threading is faster and is done every time the tape guidance function is changed. It is therefore somewhat slower and noisier than the U-system. This problem is being solved by "Quick-start" VHS video recorders, which allow fast and silent changes in tape guidance functions. To avoid excessive wear, M-tape guidance system recorders are provided with an automatic switch-off feature, activated some minutes after the recorder is put on hold, which automatically unthreads the tape. An improvement of the basic VHS system is HQ (High Quality) VHS.

In the VHS system different starting points were used than in Betamax, such as track size and relative speed. VHS has rather wide video tracks, but a slightly lower relative tape speed, and that also counts for the audio track. In general, the advantages of one aspect are tempered by the disadvantages of the other. The end result is that there is not too much difference between the sound and image qualities of both systems.


The VHS M-system before (top) and after (bottom) threading.

Video Hi8
As a direct addition to the Video-8 camcorders, there is a third system: Video Hi8, which uses a smaller cassette than VHS and Betamax. The sound recording takes place digitally, making its sound quality very good. When using the special Hi8 Metal Tape, the quality of both image and sound are equivalent to that of Super-VHS. The Video-Hi8-recorder can also be used to make audio recordings (digital stereo) only. Using a 90 minute cassette, one can record 6 x 90 minutes, making a total of 18 hours of continuous music. The video Hi8-system also allows manipulating digital images, such as picture-in-picture and editing. Video Hi8 uses a combination of the M- and U-tape guidance system.


Cassette sizes compared.

Sound Recording

Mono

In case of a mono video recorder, the audio signal which corresponds with the image is transferred to a separate, fixed audio head. As in an audio cassette deck, this head writes an audio track in longitudinal direction of the tape. This is called linear or longitudinal track recording.

The video recorder has two erase heads. One is a wide erase head covering the whole tape width which automatically erases all existing image, synchronization and sound information when a new recording is made. The other erase head is smaller and positioned at the position of the audio track. With this erase head, the soundtrack can be erased separately, without affecting the video information. In this way, separate audio can be added to a video recording. This is called audio dubbing, and can be particularly useful when making your own camera recordings.

The linear audio track does have some restrictions. Due to its low tape speed, it is not suitable for hi-fi recordings. Moreover, the audio track is so narrow (0.7 mm for VHS and 1.04 mm for Betamax) that not even stereo sound can be recorded properly. The frequency range is limited as is the dynamic range (which relates to the amount of decibels), and the signal-to-noise ratio is not very high.(The signal-to-noise ratio relates to amount of noise compared to the total signal. The higher this ratio, the less noise and the better the signal will be). The sound quality of the mono track can be improved by a noise reduction system. There is a way to get superior hi-fi stereo sound quality on a videotape (used in hi-fi video recorders,) which will be discussed later.

Hi-fi Stereo Sound

Hi-fi video recorders were developed for improved sound quality. The most common quality of video images is HQ. (The recorder is labeled 'VHS High Quality Hi-fi Stereo'). Conventional mono video recorders use linear audio registration, which does not allow hi-fi recordings. A special method was therefore devised to record stereo sound with hi-fi quality.

In the case of hi-fi, the audio signal is also put on tape via revolving heads similar to the video signal, not on the linear track. As there is no space between the video tracks, as the video tracks lie right next to each other with no space in between, the audio tracks need to be recorded in the same place as the video tracks. The way this is realized is by recording the audio signal under (deeper than) the video signal.


Hi-fi video recording, where the audio signal is recorded at a deeper level, after which the video signal is recorded on top.

In hi-fi video recorders, the audio signal is modulated to a high carrier frequency. This is realized via FM modulation, with the right channel stereo signal at a slightly higher frequency than the left channel. The corresponding video and audio signals are written to tape immediately after each other. First the FM audio signal is registered at a deep level in the tape's magnetic coating. Straight after the audio signal, the video signal is recorded. As the frequency of the video signal is higher than the audio signal, it will not register as deep in the tape coating as the audio signal. The video signal erases the audio signal in the top layer and records the video signal instead. Thus, the audio and video signal tracks are written in the same magnetic layer, separately, one on top of the other. The entire magnetic coating is only 0.004 mm thick. To ensure that the two do not interfere, the audio and video tracks are written on tape from a different angle, by means of a different head with a different azimuth setting.

To guarantee compatibility with cassettes not recorded in stereo hi-fi, the fixed audio recording/playback heads remain in place. So, a hi-fi video recorder always has two audio registration systems installed. This offers possibilities for amateur video makers to do audio dubbing using an audio mixer to combine the sound of the hi-fi track with other sounds and to write the mix to the linear audio track. In this way synchronized recordings will be left intact.

Quality Audio Recorders

A hi-fi video recorder is also suitable as a high-quality audio recorder, not only because of the professional recording quality, but also because of the long play possibilities and the low recording costs.

The specifications of hi-fi video sound registration systems equal those of professional tape decks and compact discs. The entire sound spectrum can be covered without any problems, and the dynamic range is 80 dB, close to the 90 dB that compact discs can cover. (As the video recorder is a recording medium, a couple of good microphones can actually cover the whole 80 dB range.) Recordings made on a hi-fi video recorder result in almost unmeasurable wow and flutter and very little harmonic distortion. The low tone quality of a hi-fi video recorder is remarkably good compared to tape recordings of cassette decks. A disadvantage is that sound editing is not possible via a VCR. Instead, the required tape segments can be copied unto another tape without hardly any loss of sound quality.

A hi-fi-video recorder needs to be tuned very accurately. As the two rotating audio heads function alternately, the recorded sound consists of successive particles and need to fit together perfectly. If they do not, the result is rumble, which is a humming sound. In high quality, well-tuned hi-fi video recorders you will not hear this sound.

Super-VHS

Super-VHS or S-VHS (for Betamax: ED-Beta)is a major step forward in the field of video registration. It is a recording-playback system of such high quality that its recordings are equal to the quality of direct TV broadcast signals. S-VHS offers better image quality than normal VHS, fuller colors, more sharpness, clearer color separations and color fields, and eliminate moire effects. Details not visible on normal VHS, become visible on S-VHS, such as fine fabric patterns and eyelashes. As in all video recording systems, recording image and sound on magnetic tape involves the actual image, the colors, the horizontal and vertical synchronization pulses for perfect image building, and finally the sound. S-VHS requires so much information that it takes a frequency band of 7 million Hz (7 MHz) to store all the information. As this would be too much, in S-VHS the 7 MHz bandwidth is reduced to 5 MHz, without seriously reducing the image quality.


The frequency ranges of sound, TV and VCR. The original 7 MHz are reduced to 5 and 3.2 MHz. S-VHS can register the full TV bandwidth. The Y and C signals are put separately on tape and separately transferred to the TV when played back.

Signal Separation
However perfectly the helical scan system works, normal VHS video recorders cannot register the entire 5 MHz range that comes through via a television broadcast. The bandwidth is reduced to 3.2 MHz at the expense of quality, meaning reduced sharpness, detail, and clarity of color transitions and more noise. Taking away almost 2 MHz is not a matter of simply filtering the signal, as that would lead to the loss of essential information. The bandwidth is reduced by separating the interwoven Y and C signals and putting them on tape separately. When played back, both components are re-mixed to one signal and then transferred to the television set, together with the sound and synchronization signals. In S-VHS the reduced bandwidth is brought back to its original full 5 MHz. In order to achieve this, new video heads and a superior kind of tape were developed, with higher recording density and a smoother tape surface, for optimal head-tape contact.

Resolution
Due to the increased bandwidth and the increased dynamic range of the brightness (Y) signal, the resolution of the S-VHS recording is higher than VHS. Resolution relates to the number of distinguishable adjacent vertical picture lines. As the vertical picture lines are placed next to each other and virtually placed on a horizontal line, we also speak of horizontal resolution. Increased horizontal resolution means more detail is visible, resulting in a brighter image, clearer picture lines and smoother image fields. S-VHS has a resolution of 400 picture lines, compared to 240 picture lines in VHS, and 300 in the conventional TV signal. Moreover, a sub-emphasis-circuit suppresses image noise, particularly for weak video signals and also contributes to better image quality.

In S-VHS the brightness and color signals (Y and C) are not combined in the usual manner when played back, and are not sent to the TV as a composite signal, but are transmitted separately. This separated transmission takes place via a special cable and a connection socket: the S-connection (S = Separated Y/C). The result is that the cross color between these signals is largely decreased, which has a positive impact on the color separation.

VHS - S-VHS Compatibility

The S-VHS recorder is a two-in-one recorder: an S-VHS-recorder which can also be switched to VHS mode.

S-VHS recorders are backward compatible, meaning that S-VHS recorders and tapes can handle both VHS and S-VHS, whereas normal VHS recorders and tapes cannot. For S-VHS application, special S-VHS cassettes must be used, which reach the requirements of S-VHS and have an identification slot, that makes the recorder automatically switch to S-VHS mode when the cassette is inserted. When a normal VHS cassette is inserted, the video recorder will automatically switch to VHS. It is not possible to make S-VHS recordings on a VHS cassette but normal VHS recordings can be made on a S-VHS cassette. In these cases, the result is good image quality, but not S-VHS quality. When a pre-recorded VHS cassette is played back on a S-VHS recorder, it is without the S-VHS quality. The recorder will then automatically switch to normal VHS. An S-VHS recording cannot be played back on a conventional VHS recorder, because it cannot cope with the increased bandwidth and the other improvements. The result is a distorted black-and-white image. Recordings made in S-VHS can only be played back on an S-VHS recorder.


VHS - S-VHS compatibility. Only registration of S-VHS recordings via the VHS-system is not possible.

To gain maximum benefit, TV sets to which the S-VHS recorder is connected, must be provided with S-connections. The same applies to transmission via SCART-RGB sockets. If transmission takes place via normal SCART or HF connection, the image improvement would be less impressive, although still noticeable. The advantages of S-VHS and ED-Beta become more obvious when making your own camera recordings, than in normal video and TV use. Especially when making copies of camcorder recordings, even a third generation copy suffers hardly any quality loss. This applies not only to S-VHS and Super-Beta-hi-fi, but also to the Hi8-system.

VCR Connections to TV Sets

A video recorder can be connected to a television set via antenna connection. The TV antenna is connected directly to the antenna input of the video recorder (ANTENNA, AERIAL IN, RF or HF IN. HF stands for High Frequency). The antenna output on the video recorder (AERIAL OUT or HF OUT) is connected to the antenna input of the TV via a coax cable. Both devices therefore receive a TV signal. When playing back a recorded videocassette, the video signal is sent to the antenna input of the TV via the same cable. This is possible as the video recorder has a built-in oscillator (or small sender), that generates a carrier frequency similar to the frequency of the channel reserved for VCR. The A/V-channel of the TV must be tuned to this frequency, so that the recording can be watched on the TV.

The SCART connection will give higher quality, provided there is a SCART bus on both the television set and the video recorder. Both the audio and video signals will then be sent directly to the audio/video amplifier in the TV set, instead of having to make the detour via the oscillator and demodulator, in which the audio/video signal has to be converted twice: first to the high transmission frequency and then back again. The SCART-connection also performs better when copying videotapes.

VCR Features

Heads

The minimum heads required for video and audio registration are two heads for video and one for audio (mono).

Three video heads on the head drum allow still picture without distortion and slow motion. With two heads, distortion lines might be visible on the screen, but in case of three heads, the image will be still and without stripes.


Placement of three video heads on the head drum. During recording and normal playback, heads A and B are used. For still picture heads B and B' scan the same video track for noise-free reproduction.

Besides still picture and slow motion, four video heads offers the choice between standard play and long play. Standard Play (SP) is the cassette's usual playing time. Long Play (LP) allows you to double the recording time. The video heads write tracks that are half as wide as in case of standard play. The narrower tracks mean that there is less information put on tape, which results in somewhat lower quality. In the UK there are VCRs on the market that can record in long play with only two video heads.

Hi-fi stereo audio recording via frequency modulation requires 2 additional audio heads on the head drum instead of one separate audio head for mono.


Showing a 4-head drum plus 2 audio heads for hi-fi recordings.

Flying Erase Head

Besides the separate erase heads already present in the VCR, the flying erase head is an erase head that is placed on the head drum just like the video and hi-fi audio heads. The main benefit of the flying erase head is that it makes better editing compared to the other erase heads. The flying erase head follows the video tracks in the same diagonal direction, contrary to the regular erase heads which erase all information vertically.

Timer Programming

There are several ways to set the timer on the VCR to make your own recordings. In order to make sure that the VCR knows what and when to record, the following information must be entered: start time, stop time, date and channel/program. This information can be entered directly on the VCR or via remote control. However, many people have difficulties with programming, and so, other ways of programming have been developed, some of which are described here below. VPT (Video Programming by Teletext) is a way to set the VCR timer with the help of Teletext. There are two requirements: the first is that the VCR must have the VPT feature, and the second is that the channel, which broadcasts the program you want to record, must have Teletext. By calling up the Teletext page with the program information, and pressing the VPT button, a cursor appears on the TV screen. Using the cursor, the program you want to record can be selected. By pressing the VPT button again, the program will be stored in the timer memory. With the Teletext decoder built into the VCR, it is also possible to use the VCR to display and record Teletext subtitles.

Sometimes programs start at a different time than listed in TV guides or on Teletext. VPS (Video Program System) is a system by which the broadcast station ensures that the VCR starts and stops the recording session at the proper moment, by transmitting signals which are received by the VCR. For this system to operate, the broadcast station has to use VPS, and the VCR must be equipped with the VPS feature. If the reception quality is poor, the VPS feature might not function properly. VPS comments may also appear in TV guides. Currently, this system is only operational in Germany, Switzerland and Austria.

ShowView is invented by US company Gemstar, and works by means of individual codes for every TV program. The VCR must have the ShowView feature. The numeric code, which can range from 3 to 9 numbers contains the channel, date, start and stop time information and is printed in the TV guide next to the program. By entering this code into the VCR, the timer will be set automatically.

Finally, "parallel programming" makes normal VCR timer use more simple, by continuously displaying the start time, stop time, program number and date. The user has direct access to all four settings and can adjust each as needed by remote control.

Digital Image Correction

One of the most effective picture improvements is realized by a digital image correction system. Here, every image that is transmitted by the video recorder is first sent to a memory and not directly to the screen. The memory compares the incoming image with the previous image. Any sudden irregularities, such as drop-outs or distorted lines, are immediately identified and corrected. The digital image memory offers still playback images and a perfect, stable picture-by-picture reproduction, with interval options ranging from one to many seconds.

The Videotape

Tape Characteristics

What makes a videotape a good tape? There are three characteristics which contribute to total tape quality: mechanical, magnetic and electro-acoustical characteristics.

The mechanical characteristics are related to the carrier, the thickness of the tape, the slack resistance and especially the tape guidance system behavior. The latter is a matter of cassette housing, the precision of which should meet the highest requirements, just like the tape itself. The tape guidance should always be tight but flexible, without friction, but also without getting tangled. The vulnerable edges of the thin tape should not wear, even at microscopic level or after many hours of use. Damage at the edges will have a negative effect on the sound reproduction and on the image synchronization, as this information is recorded right next to the edges. Although a VHS recorder will always switch off automatically after a couple of minutes of still playback, to avoid too much wear (the head drum is revolving inside the stopped tape, with a microscopically thin layer of air serving as a buffer), a good tape should be able to cope with a period of still playback of at least 60 minutes. Some tapes have a thin layer of coating on the back, to reduce the friction to an absolute minimum.


Close-up of a video tape.

As far as the magnetic characteristics are concerned, the tape should be resistant to demagnetizing, i.e., should have a high coercive force. The reminance, which is the magnetism that remains on the tape after the magnetism generating field is taken away is another essential characteristic. For audio tapes a high reminance is a prerequisite in order to produce a wide dynamic range, but in case of videotapes high reminance is not required, because of the high registration speed of five meters per second. The reminance of an average normal videotape has more or less the same value as that of a conventional ferro-oxide audio cassette.

The electro-magnetical characteristics largely determine the quality of the tape. These characteristics are:

Poor quality tapes are always recognizable by drop-outs (flashing lights and stripes all over the screen), bad color reproduction and sound interrupts. They can also cause the heads to get dirtier faster. Good tape quality depends largely on the very small particles on the tape surface. They should be only 0.3 microns long, and the width be smaller by a factor of 10. Just as important as the particles being equal in size, is that they also need to be spread equally. The tape thickness should be constant within a 0.1 micron range, the tape surface absolutely smooth and the tape guidance system practically perfect. Only if a tape meets these requirements, will there be a good, stable head-to-tape contact and no fluctuations in the signal and frequency levels. Such fluctuations cause modulation noise that results in unstable, unclear and misty image reproduction.

The electro-acoustical characteristics are listed by the manufacturer in a specification list. The quality of luminance signal (Y) reproduction is expressed by the video signal-to-noise ratio (video S/N). The higher this video S/N, the clearer the image reproduction will be, with improved contrast ranging from deep black to clear white. There is a reference tape that indicates the required standard. This generally accepted reference standard is 0 dB. If the tape's value is 0 dB, the video S/N is above average. But as videotapes get better, the value of a good standard tape is already much more than 0 dB, sometimes even up to +4 dB.

The quality of the color reproduction (chrominance: C) is expressed by the color signal-to-noise ratio (color S/N). The higher this value, the better the hues are reproduced and the deeper the colors are. Here too, 0 dB is the standard, but the latest tapes also achieve higher values, up to +5 dB. The video and color S/N relate directly to how equally the particles are spread on the tape surface.

HF or high frequency output level, also called Sensitivity, expresses the capability of the tape to register the high video frequencies. If this is not done properly, it could lead to, for example, an increased level of noise. Here, too, 0 dB is the reference standard. The HF level relates to the size of the particles.

Tape and Purpose

Different applications require tapes of different quality. It makes sense to use the right tape for the right purpose. There is no need to purchase a high quality tape, if the application does not require it. For almost all normal applications the Standard (or High Standard) tape will suffice. Below you will find the various VHS types. Basically, the listing also applies to Betamax; Hi8 equals S-VHS quality.

Standard or High Standard
For normal TV recordings on any video recorder

High Grade or Extra High Grade
For recordings from TV or camcorder on a modern video recorder, aiming at optimal image and sound quality.

High Grade Hi-fi or Extra High Grade Hi-fi
Recordings on a hi-fi-video recorder, striving for the highest audio quality.

High Definition PRO or HX PRO
For valuable recordings that need to stay in top condition for years or for more demanding applications with electronic tape editing. It has a slightly thicker tape.

S-VHS Video Cassette
For Super-VHS recordings on a S-VHS video recorder.

Cassette Type and Playing Time

     VHS       Playing time
     --------------------------
     E-30        30 min.
     E-60        1 hour
     E-120       2 hours
     E-180       3 hours
     E-240       4 hours
     E-300       5 hours

     Betamax   Playing time
     --------------------------
     L-250       65 min.
     L-500       130 min.
     L-750       195 min.

(Recording at half speed, long play, allows for the double recording time.)

High Speed High-Quality VCRs

A new generation of VCRs has been developed which totally redesign tape handling for higher speed and a more reliable operation of the VCR. The Philips Turbo Drive VCR was the first in this area, and remains a leader with new enhancements each year. The Turbo Drive also introduces laser-cut video heads and laser calibration with benefits to picture quality.

Design

Many of the new HQ VCRs feature a mid-mount design, which places all mechanical operation in the center of the VCR for better chassis stability. Redesigned tape handling allows for 1/3 fewer parts, which increases the reliability.

Picture Quality Control

For optimum picture quality in VCRs, the tape must be closely aligned with the video heads. There are five factors which affect this tape alignment. These are: 

     - Chassis stability
     - Tape path guide pin wear
     - Tape guide placement accuracy
     - Tape path height alignment
     - Tracking accuracy

Tape Alignment
The Turbo Drive uses a steel chassis for much more stability as compared to an aluminium chassis. Turbo Drive VCRs have metal guide pins instead of plastic ones, so that wear is reduced and alignment improved over time. In addition, these VCRs use laser welding and laser calibration.

Laser welding improves the angle tolerance of the guide pins by using precise lasers as compared to conventional welding. Over 30 points in the tape path are welded by laser.

Laser calibration improves the height tolerance of the tape guide elements, from .20 mm to .05 mm. All chassis surfaces have variations in smoothness (and therefore surface height). Laser calibration makes indentations or build-ups in the surface to restore closer tolerance in the tape path.

The tracking accuracy is improved via various digital auto-tracking systems. Tracking involves moving the tape slightly forward or back (via speeding the motor up or down one time) against the video heads to find the optimum head/track alignment position. Turbo Drive uses the Studio Tracking System (STS). STS measures the signal strength in three places in each of two video tracks, in 75 positions. This produces 450 measurements, and the optimum signal strength position can be closely identified. Because of measuring three places on each track, also non-linear tracks can be optimized.


Right: Studio Tracking System. Left: A non-linear track con be optimized.

Laser-cut Video Heads
Video heads wear down over the life of the VCR, causing an increase of the signal strength beyond normal design limits. Most VCRs allow this signal change (as much as +6 dB). Some attempt to compensate for poor head wear, by adjusting the voltage at the video head.

Turbo Drive VCRs use laser-cut video heads. They are cut by lasers, filled with glass, have much smaller tolerances and head gaps, and wear less than ordinary video heads. The innovative design maintains the near-optimum signal strength regardless of wear, throughout the VCR lifetime. It is much more precise than adjusting the voltage, which becomes unnecessary.

Studio Picture Control
Most VCRs have a permanent filter to remove noise. Noise results from a poor antenna and/or a poor/old videotape. It is caused by a weak high frequency signal, and results in 'snow' or interference on the screen.

Filters remove noise by reducing all the high frequency signals in a certain range. This removes the noise, but it also removes the sharpness. This is because the high frequency signals are used to carry the fine details. Reducing the noise also reduces the fine details.

Philips has introduced Studio Picture Control (SPC). With SPC, the tape is checked for quality (the amount of noise). Based on this check, filters are turned on or off. In this way, good tapes which have no noise are not filtered, and excellent picture detail is reproduced well. In addition, medium or old tapes are filtered medium or maximum, in order to optimize the balance between reduced noise and fine detail sharpness.

Ease-of-Use Innovations

New and more advanced VCRs have introduced a range of ease-of-use innovations to improve convenience for the user. They do this in three ways: by making 1) fewer operational steps, 2) more natural/intuitive use of controls, and 3) faster response for less waiting.

Installation
Installing VCRs can be a hassle in trying to tune the VCR tuner to the same program list and sequence as the TV tuner. It involves searching for each channel on the VCR, then finding the matching channel on the TV.

Follow TV is a Philips invention and developed to automate the process. The VCR receives the TV channel through the SCART connection. It then automatically searches the channels on its own tuner. Each is compared internally and electronically, to the TV picture. When a match is found, the VCR tuner presents the chosen signal to the user for confirmation, in the same order as the TV tuner.


Follow TV.

In addition to Follow TV, Easy Link is a system of digital two-way communication between the TV and the VCR by using the SCART cable. Using Easy Link, Follow TV completes the installation of the VCR program list totally automatically. The digital channel frequencies are retrieved by the VCR from the TV, in the same order as the TV!

Quick Recording
One of the most requested user needs in VCRs is to be able to record what one is watching, quickly and easily. Most VCRs require three steps: 1) to select VCR input on the TV, 2) to find the matching channel on the VCR, and 3) to press record.

Direct Record
Direct Record (a Philips invention) - provides an internal comparison of the picture (via the SCART cable), similar to Follow TV. The VCR is automatically tuned to the same TV program, and recording begins. The user presses only one button.

Programming for Later Recording
Storing date, program, start and stop times is a hassle for most VCR users - so much that most simply do not take the time to do it even when they would like to.

Philips has introduced "Parallel programming." This puts all four data elements on display in one view. The user moves each element independently up or down to the desired setting. One always knows where one is, and use is natural. In addition, "Time left" can be displayed so you know if you have room for what you want to record.


Parallel programming.

Operating Speed
Advanced VCRs have significantly speeded up the time to wind and rewind E180 tapes. Some have totally redesigned the tape deck so that also "eject to play" time is cut in half. This reduces waiting time and removes frustration for the user. Operating speed was the major innovation in Philips Turbo Drive.

However, most VCRs do not know exactly where they are on the tape. Therefore they can not operate at higher speeds (even if they were designed to do so), because they might break the tape when reaching the end after wind or rewind.

The Philips Turbo Drive VCR has Automatic Tape Length Recognition (ATLR). The Turbo Drive is designed to be the fastest on the market. And with ATLR, it can always operate at full turbo speed, even when starting in the middle of the tape. For the user, there are 2 benefits to ATLR:

  1. The VCR can wind/rewind at full speed on any tape, from anywhere on the tape.
  2. The VCR can tell the user how much time is left on the tape, which is useful to know when setting up a recording.

ATLR works via a microprocessor, which measures 61 revolutions of the tape wheel. By comparing to a complex algorithm built-in, the deck can predict 1% what length (time) of tape is remaining. A 10% estimate is available after 1 revolution.

Project 50

Project 50 is becoming a new industry defacto standard. It is a command and interface definition for two-way digital TV-VCR communication over the SCART cable. Because it is digital, the number of commands is virtually unlimited.

Philips and Grundig were among the first to introduce Project 50 on their VCRs and TVs. The Philips commercial name is Easy Link. When the user has both a TV and VCR equipped with Easy Link, there are the following automated functions available:

Video Index

Some VCRs are introducing a memory chip internally, which can be used to make much easier cataloguing and finding of selected sequences on multiple videotapes.

When the user first makes a recording, the VCR can know where on the tape it is, if it has Automatic Tape Length Recognition (ATLR). In addition, with Teletext, the program name can be available (over the SCART cable from the TV via Easy Link). These can be automatically stored in a memory in the VCR. (If Teletext is not available, then the user can key in a program name.)

Philips has introduced this catalogue memory called Video Index. Over 300 titles can be stored internally in the VCR, together with tape number, duration, and start position on the tape. In order to find and play a desired recorded program from one's tape library, the user does only the following:

  1. Display the recorded sequences available (including name and tape number) on the TV screen (from the VCR's memory)
  2. Scroll the list to find the one desired
  3. If the tape is not inserted in the VCR, the VCR will display a message: "insert tape."
  4. Upon insertion, the VCR automatically advances to the correct position and begins to play the sequence!

© EXIL SERVICE 1992-2017
  N.Bgd, Bul Z.Djindjica 84, Blok 30 • E-Mail: tvlcdservis@gmail.com • Tel/fax: (011) 3115-135
  w w w . s e r v i c e  . r s 
 www.service.rs  www.service.co.rs www.service.in.rs
 tv servis popravka televizora dvd servis lcd servis servisiranje televizora lcd plazma popravka monitora
 industriska elektronika popravka dvr digitalni videorekorderi servisiranje monitora