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The ATS must work the same way it did in the 8 mm. video decks. In them,
there are four rotating frequencies used. The primary on track frequency is
the strongest coming out of the head, two other frequencies are expected at
lower levels. The capstan motor is adjusted by the servo to equalize the two
off track frequencies.

At each pass of the head it uses a different frequecy for the on track
frequency and of course it expects two other frequencies just the same as
last time.

There are four frequencies and the reason for that rather than just three is
to keep it from getting confused. When F1 is recieved it KNOWS it is looking
for F2 and F4 for example, then when F2 is on track it looks for F1 and F3,
then when it goes to F3 it looks for ........ I forget. It doesn't matter,
but this should illustrate the reason to use four frequencies rather than
only three. It assures the proper operation of the servo because there can
be no mistake about which track is leading the "on" track and which is
lagging.

This system eliminates the need for a control head and errors introduced due
to tape stretching. The 8 mm. decks did actually usually have a sub audio
head but I doubt it was ever used except maybe in some super cheapo deck
which didn't even make it to market. It may have been used for a tape
counter as well, I simply don't remember those details.

Interestingly there were decks that used the 8 mm. tape strictly for audio.
The tape wrap was actually greater than 180 degrees and one sector was used
for digital audio tracks. These were not the greatest format in the world
but they beat BTSC and were good enough for music, as in better than most
cassettes. The 8 mm. decks with the feature to go all audio simply used more
sectors for more digital all audio mode. If you recorded say tracks 5 and 6
on a tape that had video on it you would see a band across the screen where
the new audio tracks were recorded. The system also had the drawback of
having to completely rewind before playing the subsequent tracks.

Needless to say these things did not get a huge market share. I just know
about them because I worked for a high end Sony dealer.

This is completely different than the auto tracking feature in any VHS deck
and I am unaware of automatic tracking being incorporated in any Beta deck,
though I might not have seen them all.

Additionally, in the DAT formet I don't know, and I simply don't remember on
the 8 mm. decks if the actually recording carrier frequency was rotated or
if they were like "pilot" frequencies simply chosen not to interfere with
the signal, but it really doesn't matter. That's how such a system works.







There's another thing I've just remembered after sleeping - DAT heads were
offset with regards to azimuth, i.e. head A was set at a very different
azimuth to head B, which made it easy to separate certain frequencies
intended for one particular head.


Gareth.