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    • CommentAuthorAsterix
    • CommentTimeJan 27th 2019
     
    A bit of both, actually. Exact track placement isn't known and neither is the recording method. These are not computer tapes, but analogue telemetry tapes.
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      CommentAuthorAngus
    • CommentTimeJan 27th 2019
     
    Just wondering whether you could use some fluid that you distribute along a section of a rolling tape long enough to acquire the domains, vacuum it up at some point via a drying blade, and read the signal out of the vacuumed fluid. Then you reel the tape up in a dry configuration.
    • CommentAuthorAsterix
    • CommentTimeJan 27th 2019 edited
     
    You have to remember that these tapes are 50 or more years old and quite fragile. You really don't want to do anything extreme to them. I don't even like the idea of exposing them to a conventional magnetic induction head. Maybe GMR...
  1.  
    What kind of physical dimensions are we talking about? I mean the magnetic features. Is the tape just a single analog track about the full width of the tape? And over what distance do the domains vary from max polarization in one direction to max in the other? I'm wondering if you could scan the tape across a sensitive Hall effect sensor. Make a transport jig, go really slowly, use a sensitive SMD ratiometric HE sensor, some low-noise amplification, etc.
    • CommentAuthorAsterix
    • CommentTimeJan 27th 2019 edited
     
    At best evidence, there are 9 tracks on the 1/2" tape, which probably moved slower than 3 Ips (best guess). Said recording is not saturation-level, as far as anyone can tell. I'm not aware of any Hall-effect sensor that can resolve details in the micron range. GMR seems like the best best, but again, linearity is an issue.

    I'll also add that some guesses indicate that the tape may be a slow-period analog data recorded as an FM signal, but we'll know more later.
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      CommentAuthoralsetalokin
    • CommentTimeJan 27th 2019 edited
     
    Well, resolving details along the length of the tape is a matter of transport speed and sensor sensitivity, isn't it? You don't need micron resolution if you can scan slowly enough, no?

    And getting 9 sensors across a half-inch tape could probably be arranged as well. Or you could use multiple passes, moving a single sensor laterally across the tape to capture a single track per pass.



    Of course I've never done this before and you're the expert... You presumably have the necessary transport system already so it shouldn't be much of a pain to try various physical sensors. Far easier than trying to use an optical method involving fluids and microfine powders, I'll wager.
    • CommentAuthorAsterix
    • CommentTimeJan 27th 2019 edited
     
    Note that we're not trying to read the tape using micron-sized iron, just trying to get the gross details. That is, we'll do about an inch or so with the powder and have a look with a microscope.

    It's something I do often with computer tapes--how many tracks, what's the bit packing density, what encoding scheme...

    Note that GMR (and MR) tape heads already exist; I'm not aware of any that use Hall-effect devices.
  2.  
    Oh, I see. You don't need to read the whole tape this way. So if you often do it with computer tapes... what's the problem with using the same system for these telemetry tapes?
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      CommentAuthorAngus
    • CommentTimeJan 27th 2019
     
    Oh yeah. Multi tracks. Forgot about that.
    • CommentAuthorAsterix
    • CommentTimeJan 27th 2019
     
    The big problem is that I don't have physical custody of the tapes--for some unknown reason, they're in the EU and I'm trying to remotely deliver some guidance. I've suggested magnetic developer, but the other end is balking at ordering some from the only existing source that I know of--shipping alone for a small bottle is over $100.

    So I'm trying to work out some locally-sourced affordable alternatives. If I actually had the tape in my possession, it wouldn't be an issue.
  3.  
    Ah. The plot thickens.

    They must not want it very badly if they are worried about a hundred dollar shipping fee. Isn't there a government involved?
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      CommentAuthorAngus
    • CommentTimeJan 27th 2019
     
    What about a liquid crystal coating with polarised light output. (I am reduced to suggesting off-the-wall research projects.)
    • CommentAuthorAsterix
    • CommentTimeJan 27th 2019
     
    No government, unfortunately--just a bunch of enthusiasts who have come into possession of Apollo telemetry tapes.

    According to the tapeheads guys, the magnetic viewer card isn't very sensitive:
    • CommentAuthorloreman
    • CommentTimeJan 27th 2019
     
    Posted By: AsterixI've got a gallon or so of DMSO, but it's hardly inert in my experience (it's used as an industrial solvent) and evaporatesveryslowly.

    HFC227 is a thought, but perhaps a little too volatile.


    You can put DMSO on your sore knees as well.
    • CommentAuthorAsterix
    • CommentTimeJan 28th 2019
     
    That's why I bought it. Curious stuff-freezes much below 18C.
  4.  
    Posted By: tinkerLimonene?


    Smells good too.
  5.  
    Posted By: AngusWhat about a liquid crystal coating with polarised light output. (I am reduced to suggesting off-the-wall research projects.)

    The idea being that the plane of polarization is rotated by the Faraday effect and should be visible in the microscope using a polarizing filter?
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      CommentAuthorAngus
    • CommentTimeJan 28th 2019
     
    Yes. No idea if it has a chance.