Re: Mark space ratio in 1531 data signal

From: Mia Magnusson <mia_at_plea.se>
Date: Wed, 11 Dec 2019 17:51:51 +0100
Message-ID: <20191211175151.00006715_at_plea.se>
Den Wed, 11 Dec 2019 00:08:05 +0000 skrev smf <smf_at_null.net>:
> The second has a much higher frequency, which might even get filtered
> out entirely by the datasette's analogue path.

Has anyone really examined the bandwidth of the electronics of the
Datasette?

In general one limit is a combination of the width of the rec/play
head (not the complete assembly but the actual active electromagnetic
part) in combination with the tape speed.

With a given tape speed, a given frequency can be expressed as full
waveforms per length measurement. If that length equals to the width of
the head, no signal can be read by the head as it always sees an
average of one full waveform. Frequencies below that can be read feely
by the head. It's kind of possible to read some higher frequencies but
it's not that useful and requires specific considerations. With various
manufacturers of the heads used in various tape units, you can't really
count on this.

(BTw for recording you rather want a head that's wide, as a wider head
can push more magnetic strength to the tape. Therefore the more
expensive/better audio tape recorders have separate heads for recording
and playback. Due to this conflict you can also at least in theory gain
better playback on tape units that has no record function, than on tape
units using the same head for recording and playback. In practice I
assume that it were mostly car stereos that actually used this, as
those usually had specific heads with electromagnets for all four
tracks to be able to play both sides by just running the tape in both
directions (and having two sets of capstan axles and pinch roller - one
for each direction). I assume that most other playback-only devices
usually used the same heads that were mass produced for units that can
also record. Perhaps some of the more expensive Walkman type products
might also have had better heads).

And then there is the electronics. The bandwidth wasn't that great on
some of the OP amps used back in the 70's/80's, so there might a limit
there too. Although it looks like the schematics actually has three
amplifier stages before the schmidt trigger waveform shaper, and in
general that means better bandwidth (as compared to using more
amplification gain from fewer op amps to gain the same total gain), so
it might not be that bad.

It's probably not that hard to find datasheets for the OP amps. However
it's most likely the tape heads and the tapes that set the limit.

-- 
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
/_|_\ We have cookies.
Received on 2020-05-29 23:52:47

Archive generated by hypermail 2.3.0.