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Betamax U-Loading

The tape path is as follows, 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 feedbackbut in a few advanced models notably theSL-C9a sophisticated electronic system is used.

After the tension arm the tape travels past a few more guides and entersthe video drum assembly after passing the full tack erase head.The guides serve to 'bias' the tape ribbon onto the drum cylinder ruler edge.

Tape travels around the drum on a 186 degree wrap and leaves the drum assembly tothe audio and control track heads which incorporate ceramic plates toguide the tape. Next the tape passes between the capstan drive spindle and the pinchroller, which performs the tape drive. After this the tape passes throughperipheral guides before re-entering the cassette shell. The take upspool is lightly driven to provide take up tension and ensure there is noslack.

Unique to the Betamax format are two small springs which tension plastictips to bias the tape as it travels around the drum. The video head tipcontacts 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 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.

Metallic leader tape

There was no room for a guard band between video track because this wouldhave resulted in too small a recording time for the given tape lengths.This meant that azimuth slant techniques were needed to minimise cross-talk between adjacent video tracks. The slant angle is +/- 7 degrees which meant that with a track angle of 5 degrees 58 seconds and a track width of 32 micronsit was not possible to achieve a noise free picture in freeze frame mode unlessa special effect head was employed.

Tape end sensors in the Beta format operate on an inductive system, with eachsensor being a coil forming part of an oscillator tuned circuit. Betamax leadertape consists of metallic material that, when they come into the proximityof the sensor, cause it to saturate and the oscillator to stop.

The audio signals are modulated on to two carriers, one at 1.44MHzand the other at 2.10MHz. The deviation is 500KHz in contrast to150kHz for the rival VHS format. The tracks are laid downso as to straddle the gaps in between the video tracks. The azimuthoff-set is 30 degrees.