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very small low power simple transmitter (ideally single chip)?

Discussion in 'Electronic Design' started by megoodsen, Aug 18, 2006.

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  1. megoodsen

    megoodsen Guest

    I'd like to build a very small, low power RF transmitter circuit that
    is small and light enough (and cheap enough not to worry about) to be
    attached to a cats collar.
    I just want it to transmit either a constant or pulsed carrier (pulsed
    prob best for battery life) of a known frequency, that I can monitor
    with a receiver and DF antenna.

    There must be single chip transmitters about these days?

    Anyone suggest suitable circuit?
  2. something like this?

  3. megoodsen

    megoodsen Guest

  4. megoodsen

    megoodsen Guest

    One more Q..

    Where might I source in a suitable small crystal for operation at
    somewhere between 144 and 146MHz?

  5. Barry Lennox

    Barry Lennox Guest

    The best commercial tags still seem to use 2 or 3 transistors, with
    the smallest available SMD parts.

    If you want a lot of choice, and various circuits to experiment with,
    I'd recommend you ask your local library to see if they can get the

    "Scientific American" (Amateur Scientist columm, pgs 128-134) of March
    1968 . You can get all the Amateur Scientist articles on 2 x CDs for
    about $30 now.

    "Mammal Review" pgs 118-141 Dec 1978. (This one is very good, and
    very practical)

    "Biomedical Telemetry", MacKay 1968 (Wiley and Sons)

    "Wildlife Radio Tagging, Equipment, Techniques and Analysis",
    Kenward, 1987

    "A Manual for Wildlife Radio Tagging", Kenward, 2001.

    The last two are pretty comprehensive, but include a lot on collecting
    and analysing data, probably not what you need.

    Barry Lennox.
  6. Phil Allison

    Phil Allison Guest

    ** Groper alert !

    ** Lotsa luck - that schem is fake.

    Cat collar transmitters and receivers are commercially available.

    But only absolute fuckwits buy them.

    Go ahead - make my day.

    ......... Phil
  7. ....and I'm sure you have the ham radio license required for transmission in
    this band? And if you do, why are you asking the question in the first

  8. Luhan

    Luhan Guest

    I'd buy one of those $5, 418 Mhz transmitters. Then you need a
    PIC12F200 running in low power mode to send bursts of signal and extend
    the battery life.

  9. Luhan

    Luhan Guest

    Ooops, that would be PIC10F200. 53 cents from Mouser.

  10. BobG

    BobG Guest

    Why not bootleg something low power on the bottom end of the AM band
    and sniff it with a regular radio?
  11. Rich Grise

    Rich Grise Guest

    An antenna that would be at all effective on the AM band wouldn't fit
    on a cat. :)

    Radio Shack has key fob transmitters, but you'd have to hack a little
    micropower pulser, maybe a CMOS 555, or a 556 to do bursts.

    A PIC, maybe, if he already has the development kit and knows how to
    program it.

  12. Luhan

    Luhan Guest

    Hey, I believe I've been 'misquoted'!!!

  13. Mark

    Mark Guest

    If it's under 100mW, is that not legal?

  14. Is there an accepted band for use with animal tracking, rather than
    ther usual unlicenced bands?


  15. No. it has to be on specified band segments. Wade through CFR 47 for
    all the regulations for the US. Most other countries have similar
    regulations and laws.

    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
  16. John - KD5YI

    John - KD5YI Guest

    No. For Part 15 rules (unlicensed operation), see

    which says, in part....

    Subpart C_Intentional Radiators

    Sec. 15.209 Radiated emission limits; general requirements.

    (a) Except as provided elsewhere in this subpart, the emissions from

    an intentional radiator shall not exceed the field strength levels

    specified in the following table:



    Frequency (MHz) Field strength distance

    (microvolts/meter) (meters)


    0.009-0.490...................... 2400/F(kHz) 300

    0.490-1.705...................... 24000/F(kHz) 30

    1.705-30.0....................... 30 30

    30-88............................ 100 ** 3

    88-216........................... 150 ** 3

    216-960.......................... 200 ** 3

    Above 960........................ 500 3


    According to the above, you are allowed 200 uV/m at 3 meters.

    This is equivalent to 13 nanowatts of isotropically radiated power.

  17. Luhan

    Luhan Guest

    I guess that makes my 500 milliwatt, 560,000 Gigahertz transmitter

    (LED flashlight)

  18. Rich Grise

    Rich Grise Guest

    It might be called out on this:"allochrt.pdf"

    Or you could look at Radio Control eauipnent - they seem to be allowed
    a decent range, and AFAIK they don't need licenses. Have you ever been
    to a place where a bunch of folks are flying RC planes? They each have a
    streamer attached to their antenna, and the color of the streamer
    corresponds to which freq. they're on in the channel - it's sort of a
    gentleman's agreement that they won't step on each other's signals.

    I have no idea what the common frequencies are[1] - a cat would look a
    little funny with a 6' whip antenna sticking out of its collar. ;-)

    Good Luck!
    [1] ISTR somewhere around 27 MHz and somewhere around 49 MHz, but quote
    me at your own risk! :)
  19. Rich Grise

    Rich Grise Guest

    And even less, if your antenna has gain, right? Because it still has to
    be < 200 uV/m at 3 meters, looking right up the throat of the antenna,

    So, what's the deal with those RF modems with thousands of meters' range?
    Are they, like, pre-licensed or something?

    And will a signal that weak reach an RC airplane that's, say, 300m away?
    Anyway, here's some frequencies:

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