I need an educational guess on frequency

Discussion in 'Wireless & RF Design' started by mik3ca, Apr 25, 2008.

  1. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    yesterday, as I was buying electronics, I bought a pair of kids walkie-talkies, so that I can rip one apart, and synchronize my transmitter and receiver with them.

    The only controls on the walkie talkies are the on-off switch, a button (when pressed, transmits pulses), and the push-to-talk switch.

    After I bought them, (because the price was cheap), I discovered that they were set to only one frequency.

    I tested them against my commercial radio. If the commercial radio is about 50 centimeters or less away from the walkie talkie, the walkie talkie can transmit somewhere between 99Mhz and 101Mhz range.

    If the commercial is at least 1 meter away, it won't pick any of the walkie talkie signal up.

    so the only thing I won't know for sure is the actual (resonant) frequency these walkie talkies are transmitting on.

    I'm guessing 49Mhz, but I am not 100% sure.

    and the package makes no mention of the frequency.
     
  2. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Years ago in the States, single channel walkie-talkies transmitted on CB radio channel 14, or 27.125 MHz.
    But if your walkie-talkies are GMRS or FRS, they would be using a different frequency.
    FRS frequencies:
    http://www.csgnetwork.com/frsfreqtable.html
    GMRS frequencies:
    http://www.csgnetwork.com/gmrsfreqtable.html

    Since you are in Canada, the frequencies may be very different.
    There were differences in Canadian vs U.S. CB radio channel frequencies, but it's been so long now that I don't remember.
     
  3. SgtWookie

    Expert

    Jul 17, 2007
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  4. mik3ca

    Thread Starter Active Member

    Feb 11, 2007
    189
    0
    ok thanks.
     
  5. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The harmonic from a walkie-talkie is 100MHz. The superhet radio has an image frequency of 110.7MHz or 89.3MHz.

    110.7MHz is the 4th harmonic of 27.675MHz which is probably the carrier frequency of the walkie-talkies.
    99.8 is the second harmonic of 49.9MHz. The walkie-talkies could be using it.

    There is the schematic of a 49mHz walkie-talkie linked in Google. It uses only 3 transistors and a quartz crystal. It is an extremely poor quality (cheap) circuit.

    I bought a pair of FRS radios on sale. They have excellent performance, a long range and were inexpensive.
     
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