At 11:41 AM 8/3/2026, Paul Koning wrote:
> On Aug 3, 2026, at 1:59PM, Len Shustek via cctalk
<[email protected]> wrote:
>
> At Sat, 1 Aug 2026 20:42:23 -0400, David Gesswein
<[email protected]> wrote:
>> The reader is a bunch of instrument amps that amplify to levels usable by
>> Saleae logic 16 pro which has analog digitization mode and way too many
>> times repurposed code to decode it. Doesn't look like I have put it online
>> probably because the code is embarrassing but ok with giving it away if
>> someone has use for it.
>
> Here's an alternative to consider: Years ago I wrote a program to decode
> waveforms digitized from cruddy old mag tapes in various formats,
> including 7-track NRZI, 9-track NRZI, PE, and GCR, and 6-track Whirlwind.
> https://github.com/LenShustek/readtape
> We've read hundreds of tapes, mostly digitized using a Saleae analyzer.
> I never wrote a DECtape decoder, but it would be doable.
Clearly, yes. One problem is that you'd need a suitable tape
head. All the rest is just software.
It sounded like David has already done that, and has digitized the analog
track data. That's what my "just software" program expects as input.
Did you use one of those high track count MR heads that some others
have used, so you can deal with funny track counts? I know of some
1/2 inch tape with 10 tracks (Electrologica X1).
No, we used vintage 7- and 9-track heads. The oddballs were the 6-track 1/2"
Whirlwind tapes, but it turns out that 6 of the 9 tracks read on a 9-track
head are close enough to the Whirlwind tracks to get strong signals without
any track-to-track crossover.
