Deciphering an odd floppy disk format.

Mattis Lind mattislind at
Sat Feb 13 11:18:28 CST 2021

I have a few 8 inch floppy disks coming from a Q1 Lite computer. I tried
reading them on a PC with a Adaptec 1522A floppy controller but it failed

Then I tried my Catweasel and dumped the raw flux data. The format differs
from what I have seen before.

I did a quick histogram of the flux lengths and it appears that there are
four groups of sample lengths evenly spaced. Peaks at 30, 48, 66 och 84
samples flux lengths.
The longest flux lengths are interspersed in between more normal flux
lengths in the actual data and I get the same type of result regardless of
reads of the same track and between different tracks. But the relative
frequency is much much lower for the longer flux lengths than the shorter

An  RX02 (MFM ish) had 26, 41, 55 samples as the peaks in the histogram.

As far as I understand cw2dmk software uses 14 MHz setting in the catweasel
so each sample length is around 70ns.

Anyone that has seen this kind of format before? Or is it just a reading
error? I have the same result from several discs though and they look to be
in quite good shape physically.

Link contains histogram files and a raw track flux file.

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