Why is video inverted for transmission?

Discussion in 'Digital Photography' started by Green Xenon [Radium], Sep 20, 2007.

  1. Green Xenon [Radium]

    Jerry Avins Guest

    glen herrmannsfeldt wrote:

    ...
    Yellow: interesting. The best yellow glazes I've seen contain uranium.

    ...

    Jerry
     
    Jerry Avins, Sep 25, 2007
    1. Advertisements

  2. Green Xenon [Radium]

    Allen Guest

    Especially since his post was made later than mine.
    Allen
     
    Allen, Sep 25, 2007
    1. Advertisements

  3. Green Xenon [Radium]

    Jerry Avins Guest

    Spark-gap transmitters used tank circuits. Even Hertz's original
    microwave transmitter used a resonant circuit, the tuned transmitting
    antenna. Each spark excited the tank to ring for a few cycles, with
    heavy damping. (What we now measure in time constants was called
    "logarithmic decrement".) Most had no way to keep the phase of one burst
    coherent with the preceding one, so splatter was heavy. (Various ways to
    achieve coherence were truly ingenious.)

    Spark-gap transmitters of any purity are illegal in US jurisdictions
    because the FCC says so. Likewise illegal, no matter how stable it may
    be, is an AM modulated oscillator.

    Jerry
     
    Jerry Avins, Sep 25, 2007
  4. Green Xenon [Radium]

    Jerry Avins Guest

    About as many as discrete transistors: too many. One synchronizes in
    other ways. I remember when only very sophisticated scopes had triggered
    sweeps. (Was Tektronix the first?)

    Jerry
     
    Jerry Avins, Sep 25, 2007
  5. Green Xenon [Radium]

    Jerry Avins Guest

    It was called a "Nipkow disk", after the inventor. The spiral pattern of
    holes was quite ingenious. It was a 2D version of what later became
    facsimile technology.
    :) ...

    Jerry
     
    Jerry Avins, Sep 25, 2007
  6. Green Xenon [Radium]

    Ron Hunter Guest

    Grin.
    Now there is a great idea, uranium glass for radiation shielding....
    BTW, is there a warning on those lead glass bricks about not eating
    them, or letting children play with them? More paranoia.
     
    Ron Hunter, Sep 25, 2007
  7. If you would read the adjacent post I made on this very subject
    Remember that propogation of Usenet posts is "best-effort"
    store-and-forward. There is no "handshaking" or feedback
    mechanism to ensure transmission or reception. Remember
    also that time/date stamps are not necessarily coordinated.
    And finally, remember that every different Usenet NNTP server
    may display messages in a different order than what you are seeing.
     
    Richard Crowley, Sep 25, 2007
  8. Green Xenon [Radium]

    Joel Kolstad Guest

    Ah, ok. Interesting... I suppose such a rule probably made a lot of sense at
    one point.

    I suspect that if one managed to build a spark gap transmitter for, say, the
    HF amateur bands that had good enough filtering to splatter no worse than a
    typical commercial radio, you would at least be pretty low on the FCC's list
    of people to prosecute. :)
    As opposed to a leveled oscillator with a separate modulator? Aren't things
    like 49MHz kids (100mW) walkie talkies something like three transistors that's
    someone's very creative kludge (the same transistors work for transmitting and
    receiving) but that is still some sort of "amplitude modulated oscillator?"
     
    Joel Kolstad, Sep 25, 2007
  9. Somewhat OT, an 1895 demonstartion of microwaves
    http://www.tuc.nrao.edu/~demerson/bose/bose.html


    Martin
     
    Martin Griffith, Sep 25, 2007
  10. Green Xenon [Radium]

    Jerry Avins Guest

    Ron Hunter wrote:

    ...
    It might be good shielding. Uranium is far heavier than lead, and
    "spent" uranium is less radioactive than many other elements.

    Jerry
     
    Jerry Avins, Sep 25, 2007

  11. I have a roll of metaized mylar film from the Sprage plant that was
    closed in teh Orlando area, years ago, along with a 20 pound spool of
    component lead. Capacitors aren't hard to make, but why bother, these
    days? Try keeping a 50 year old broadcast transmmiter on the air when
    there are no spare parts availible.


    WHEN did he operate it? Spark is not a legal mode, and hasn't been
    for a LONG LONG time. Even with a tuned circuit to couple the RF to the
    antenna, the broadband noise will wipe out other communications. Spark
    was replaced by Alexanderson generators.

    When more uses were found for the radio spectrum, spark was made
    illegal.

    http://en.wikipedia.org/wiki/Ernst_Alexanderson


    --
    Service to my country? Been there, Done that, and I've got my DD214 to
    prove it.
    Member of DAV #85.

    Michael A. Terrell
    Central Florida
     
    Michael A. Terrell, Sep 25, 2007
  12. Green Xenon [Radium]

    Jerry Avins Guest

    If the power is low enough, they don't care. But the rules definitely
    apply to a 5W, or even a 2W set. Those are crystal controlled -- perhaps
    via a PLL -- and the modulated stage is not the oscillator.

    Jerry
     
    Jerry Avins, Sep 25, 2007
  13. Probably circa 1920. When he told me the stories I wasn't much
    interested in dates.

    In the mid-50's the AWA Museum had a operating permit for a spark gap
    transmitter that allowed them to operate for up to 5 minutes with no
    antenna attached. At that time nothing within 10 miles except farms.
    Definitely impressed me as a teenager.
     
    Richard Owlett, Sep 25, 2007
  14. Green Xenon [Radium]

    Jerry Avins Guest

    Michael A. Terrell wrote:

    ...
    I was once so far out in the Atlantic that the Coast Guard, who were
    looking for us in Long Island Sound, found us only by accident and that
    only after five hours of motoring closer to shore. The motor had quit
    the afternoon before, then a storm came up. We drifted as far as we did
    because of the tide pulling us out with a sea anchor I gas improvised to
    keep from getting swamped by waves.

    Come first light and a calm sea, I got the flywheel off and figured out
    that the condenser was shorted. I made a replacement from four sheets of
    foil-lined paper from cigarette packs -- smoking saved our lives -- that
    worked well enough to get us under way. There are plenty of reasons to
    make capacitors. :)
    Marine spark equipment was grandfathered for a long time after it was
    banned on land. You didn't need a BFO to read it precisely because it
    wasn't CW. A late friend was a passenger in a two-seater in Alaska that
    broke up on making an emergency landing. He improvised a spark-gap
    transmitter using the battery and spark coil, as well as other wires
    ripped out of the plane. For two hours he alternated between tapping out
    his best-guess position and keeping fire going. Then a plane dropped
    survival equipment and food. Two hours later yet, a helicopter landed
    and picked them up. He asked the crew if his signal had been heard of if
    they had been found by accident. "Hear you" came the answer. "You were
    all over two bands. Nobody could hear anything else." To quote the Edda,
    "Even the black dog will have its day."
    Jerry
     
    Jerry Avins, Sep 25, 2007
  15. Green Xenon [Radium]

    G Guest


    When I was fairly young I got a remote control bus for Christmas. it used a
    spark gap transmitter. The receiver used a powered carbon detector.
    Every time a signal was found, the carbon would start to conduct and fire a
    relay setting up action on the preprogrammed mechanics and motor. When
    an action ws complete, a arm would come down a hit the carbon detector
    to break conduction and get ready for another command. it used to trigger
    on lightning. I got my first real shock when i unscrewd the insulated antenna
    out, and stuck my finger in the hole and pushed the button. I guess
    that was my first electronic project, except my mother used to tell me about
    the time when I poured water into a lamp socket. It goes buzzz.

    greg
     
    G, Sep 25, 2007
  16. Oh - Thunderbird. I use it for e-mail. Its spell checker is very
    bizarre, IMHO :)

    Luckily I also use the organic spell checker after a pass or three of
    Thunderbird's. When I remember to do it, that is...

    I use a bunch of spell checkers (not by choice - each program seems to
    have a checker of its own), and they *all* are bizarre - it's just that
    what one screws up the next does fine, etc :)
     
    Gene E. Bloch, Sep 25, 2007
  17. Jerry Avins wrote:

    (snip)
    Trying to remember non-electronic ignition systems, I thought they
    would work without the capacitor. (or condenser as I remember it.)

    The points would ark more and wear out faster, but probably not
    so fast that you wouldn't get back to shore.

    -- glen
     
    glen herrmannsfeldt, Sep 25, 2007
  18. Ron Hunter wrote:

    (snip)
    There are plenty of things in physics labs that do radiation
    work that don't have warnings on them. I would expect lead glass
    bricks to be less of a problem than solid lead bricks.

    The usual problem with lead crystal goblets is acidic liquids
    that can dissolve some of the lead out. Usually lead glass bricks
    are not stored in acidic liquids.

    -- glen
     
    glen herrmannsfeldt, Sep 25, 2007
  19. Jerry Avins wrote:

    (snip on lead glass bricks)
    As I remember them, lead glass would be a fairly light yellow.
    You could look through a three or four inch thick brick and it still
    looked light yellow. As a thin glaze, you might not notice it.

    -- glen
     
    glen herrmannsfeldt, Sep 25, 2007

  20. Beryllium oxide transistor pads are dangerous! Don't cut your finger
    with one!
     
    ChairmanOfTheBored, Sep 26, 2007
    1. Advertisements

Ask a Question

Want to reply to this thread or ask your own question?

You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.