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RF through water question

Discussion in 'Electronic Design' started by Ron H., May 11, 2004.

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  1. Ron H.

    Ron H. Guest

    What are the design issues involved with passing medium wave ( 10s of MHz )
    higher power ( KWatts) RF through a water jacket. Assume "tap" water and of
    course non conductive non ferrous housing material.

    Ron H.
     
  2. Checkout: http://www.qsl.net/vk5br/UwaterComms.htm

    --
    Scott

    **********************************

    DIY Piezo-Gyro, PCB Drill Bot & More Soon!

    http://home.comcast.net/~scottxs/

    **********************************
     
  3. Guest

    Um.. unless your water is de-ionized or distilled, you don't pass RF through it.
    It gets absorbed and turned into heat just like in a microwave oven. Tap water
    is not de-ionized.
     
  4. At a frequency somewhere around 1 gigahertz, water (even pure water)
    changes from a dielectric to a lossy dielectric. At frequencies well
    below 1 gigahertz, water should perform much like any other high
    dielectric constant material, with loss depending mainly on the
    conductivity and thus the ionic contaminants.

    See:
    http://www.lsbu.ac.uk/water/microwave.html
     
  5. Tim Auton

    Tim Auton Guest

    How do you think they talk to submarines? (the answer is: slowly!) You
    can pass RF through water (even sea water), but unless it's very low
    frequency (or extremely low - ELF) it doesn't get very far. You'd get
    serious attenuation with 10s of MHz.


    Tim
     
  6. Tim Auton wrote...
    For the most part, with acoustic signaling. And sub-20kHz ELF,
    but only if the sub is near the surface and trailing an antenna.

    Thanks,
    - Win

    (email: use hill_at_rowland-dot-org for now)
     
  7. Read and understand one of my favorite texts or one of its successors: Ramo
    and Whinnery, "Fields and Waves in Modern Radio." Learn how to calculate
    skin depth. Look up appropriate values for conductivity and dielectric
    constant. End up by doing the calculations. They are easy using a modern
    scientific calculator.

    Otherwise, send me a check for $200, and we can negotiate what you get for
    that.

    Bill
     
  8. maxfoo

    maxfoo Guest

    like this...

    http://www.darpa.mil/ato/programs/bcaa.htm




    Remove "HeadFromButt", before replying by email.
     
  9. Tim Auton

    Tim Auton Guest

    AFAIK VLF (3-20kHz) is only used near the surface with a trailing
    antenna, but the latest ELF systems have neither requirement. What I
    can find on the ELF system in use by the US (76Hz) suggests they can
    receive ELF at operational speed and depth, which doesn't suggest
    "near the surface" to me. It's all relative of course and hard figures
    are hard to come by (hardly surprising!), but I've seen 2-300m
    mentioned. AIUI they use on/in-hull antennas (presumably SQUID based)
    instead of trailing wire antennas for ELF too.

    OK, perhaps it's not how they /usually/ talk to submarines though :)


    Tim
     
  10. Wow, 76Hz? And this stuff is being discussed in public?

    Thanks,
    - Win

    (email: use hill_at_rowland-dot-org for now)
     
  11. Tim Auton

    Tim Auton Guest

    76Hz indeed. Wavelengths of thousands of km. Antenna *feedlines* tens
    of km long. It's fascinating stuff. If it's meant to be a secret
    they're not doing a very good job of keeping it :)

    Do a search, there's info out there on the 'net ('ELF submarine'
    should get you started). Here's some info on the Russian equivalent
    system (Zevs) that gives a pretty good overview.

    http://web.tiscali.it/vlfradio/zevs/zevs.htm


    Tim
     


  12. Yes. About 10 or so years ago, when I worked for a company who made variable
    speed motor controllers, an engineer with Continental Electronics called and
    asked about our 250 kW inverters. During the question/answer process, it
    came out that he wanted an output of about 250 kW with frequency variation
    of something less than 60 Hz to near 100 Hz to communicate with submarines.
    Huh? I said, you can't pass any information with a carrier at that
    frequency. He said it all depends on how it's modulated and how much time
    you take to decode it. That shut me up.

    I'll never forget that phone call.

    John
     
  13. bushbadee

    bushbadee Guest

    Messages can be transmitted by morse code at those frequencies.
    But we have better methods now of communicating with Subs under the water.
    It is called Blue light which penitrates sea water to pretty good depths.
    They do not talk about it much but if you can talk to a sub with blue light,
    then you should be able to detect bounce back and locate subs under the
    ocean.
    I forget for the momment the names of those lasers.

    I once worked on a laser of that type and the voltage was so high that it
    made it's way around about 4 feet of Plexiglass insulator to spark. Left a
    carbon streak on the Plexiglass and it had to be replaced.
     
  14. Max Hauser

    Max Hauser Guest

    "Repeating Rifle" in news:BCC6A5B1.173B6%...:
    Or if you are really, really desperate, search Usenet archives for the
    phrase "skin depth" in the year 1987.

    There you may read (with growing awe, if you know the subject) one Commander
    Brett Maraldo describing speaker cables of mercury-filled tubing, and an
    ensuing Grand Debate -- as popular then as now -- on skin depth in
    conductors: one camp insisting that depth of penetration is the electrical
    wavelength at frequency, and the other group countering that it's the (!)
    acoustical wavelength instead.

    (At that time, and also in a follow-up, I too cited Ramo and Whinnery. For
    what good it did, but maybe it did, who can say?)

    Max
     
  15. Max Hauser

    Max Hauser Guest

    "The other John Smith" in message
    You're damn right it does. (The intuitive notion of a tight relationship
    between bit rate and analog bandwidth disappears like parted waters if you
    study communication theory -- you can have data rates far greater or far
    less than bandwidths, in exchange for requirements for SNR or other
    constraints.) But the subject tends to the counterintuitive, so it
    collects notions and suppositions and opinions. (Like various other areas
    of electronics.) This by the way is partly the domain of the newsgroup
    comp.dsp .
     
  16. There is not much secret to it. The physics is well known and not
    complicated. The trick will be to implement a working system. That is not
    easy. There will be no way to prevent interception. I am sure that any
    potential adversary is listening now. The key will be encryption and hiding
    that there may have been successful communication.

    Bill
     
  17. I sometimes wonder about the sanity of some audiophiles. Although many do
    indeed know what they are talking about, others are like Art Bell. What else
    would explain the love affair with tube ampifiers, monster litz cables,
    vinyl records over compact disks, and my favorite, a green marker to green
    up the area around a CD spindle hole? To tell the truth, I have not heard
    much about that last on letely. Is it still in vogue?

    Bill
     
  18. Fascinating. Here're a few quotes from that site:

    Why use ELF? "In the middle of the Atlantic ocean, with a salinity
    of 3.2%, a VLF signal will penetrate down to a depth of 10-20
    meter, barely periscope-depth for a modern large scale submarine."

    "At the Zevs' military operating frequency (82Hz), the wavelength
    more than 1/4 of the earth's diameter."

    "frequency shift observed, in the narrow range 81Hz to 83.3Hz...
    The carrier shift of only 2.3Hz makes up the difference in a mark
    and a space of the MSK signal. ... The ELF carrier frequency is
    shifted from the normal carrier frequency of 82Hz, down to 81.6Hz
    and up to 82.7Hz, prior to this message. This is most likely the
    'message waiting' call function of the Russian ZEVS transmitter."

    "The coded message sent is a repeated, error correcting code. The
    bit rate is a few bits per minute, repeated until enough data..."

    Thanks,
    - Win

    (email: use hill_at_rowland-dot-org for now)
     
  19. In message <>, Winfield Hill

    [snipped]
    I bet they're mightily pissed off by HTML messages.

    Cheers
     
  20. Keith Wootten wrote...
    Yes, and no binary attachements allowed.

    Thanks,
    - Win

    (email: use hill_at_rowland-dot-org for now)
     
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