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Consumer Video Formats
Betamax
The
Betamax system was developed by Sony
Beta was the first widely used consumer video
recording tape format. It was made by
Sony. At one time Beta machines were also sold
by several other retailers. |
Supporters of Beta
believed that the picture and sound quality of Beta was superior to VHS. Eventually VHS overtook Beta in the
consumer market, ultimately leading to the almost complete
disappearance of Beta machines and pre-recorded Beta tape.
The
tape leaves the supply (left hand ) spool via
internal guide posts and travels around the
tension regulator. In most models the back
tension is regulated by mechanical feedback but
in a few advanced models a sophisticated
electronic system is used.
After
the tension arm the tape travels past a few more
guides and enters the video drum assembly after
passing the full track erase head. The guides
serve to 'bias' the tape ribbon onto the drum
cylinder ruler edge.
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Tape travels around the drum and leaves the drum assembly
to the audio and control track heads which incorporate
ceramic plates to guide the tape. Next the tape passes
between the capstan drive spindle and the pinch roller,
which performs the tape drive. After this, the tape passes
through peripheral guides before re-entering the cassette
shell. The take up spool is lightly driven to provide take
up tension and ensure there is no slack.
Unique to the Betamax format are two small springs which
tension plastic tips to bias the tape as it travels around
the drum. The video head tip contacts the video head at
the bottom edge and leaves it at the upper edge. The video
head rotates in the same direction as the tape moves.
The tape is 1/2 inch thick (same as VHS) and has
the audio track at the top and the control track
at the bottom edge. The original Betamax
specification defined a single audio track
1.05mm wide. When the format was later revised
to allow for a stereo sound track it was
necessary to squeeze both tracks into the
original space which gave disappointing results. |
There was no room for a guard band between video
tracks because this would have resulted in too
small a recording time for the given tape
lengths. This meant that azimuth slant
techniques were needed to minimize cross-talk
between adjacent video tracks. With this
arrangement it was not possible to achieve a
noise free picture in freeze frame mode unless a
special head was employed. |
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Tape end sensors in the Beta format operate on an
inductive system. Betamax leader tape consists of metallic
material that, when they come into the proximity of the
sensor, cause it to saturate and the oscillator to stop.
To improve the sound quality Sony developed Beta Hi-fi.
This recorded Hi-fi quality sound as FM audio tracks by
means of separate audio heads mounted on the video drum.
The audio signals are modulated on to two
carriers, one at 1.44MHz and the other at 2.10MHz. The
deviation is 500KHz in contrast to 150kHz for the rival
VHS format. The tracks are laid down so as to straddle the
gaps in between the video tracks. The azimuth off-set is
30 degrees.
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Betamax
Specifications |
Tape Width |
1/2 inch |
Drum Diameter |
74.487 mm |
Speed of Head
Disc |
1500 rev/min |
Video Head to
Tape Speed |
5.832 m/s |
Tape Speed (PAL) |
1.873 |
Video Head Gap |
0.4 microns |
Tape |
Length |
Running
times for BETA |
PAL
SECAM |
NTSC
BI |
NTSC
BII |
NTSC
BIII |
L-125 |
125 ft |
30 mins |
15 mins |
30 mins |
45 mins |
L-165 |
165 ft |
45 mins |
22 mins |
45 mins |
65 mins |
L-250 |
250 ft |
65 mins |
30 mins |
60 mins |
90 mins |
L-370 |
370 ft |
95 mins |
45 mins |
90 mins |
180 mins |
L-500 |
500 ft |
130 mins |
60 mins |
120 mins |
210 mins |
L-750 |
750 ft |
195 mins |
90 mins |
180 mins |
270 mins |
Contact: email [email protected]
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