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Advice on building a radio transmitter in the Radio Control band

  1. Mar 13, 2015 #1
    << Mentor Note -- post separated out of a different thread to deal with a separate question >>


    I am looking transmit as well as receive power within close proximity.
    Currently I am looking at 27.255 MHz AM in the citizens band.
    It is listed on Wikipedia and in statues I found to be for radio controlled devices, as in not to be used for communication. The particular channel has a max power of 25 watt.

    The current setup I want to have the emitter and receiver approximately 3m apart.

    I have done a rough calculation of the per square meter flux by representing it as a sphere of 3m radius.

    I have yet to look into the optimal type of antenna for sending/receiving but approximated the receiving as a disc of 10cm diameter. It looks like resonant antenna of 5.5m length is important here. (wavelength = 11m)

    This calculated power available is well above the power I want for charging my devices battery.

    I am interested in any information I can get on antenna configurations, as well as any information on any interference that could come about from this set up.

    The transmitter I understand will be a crystal oscillator tuned to 27.255 MHz put through some type of amplifier to boost its power.
    Last edited: Mar 13, 2015
  2. jcsd
  3. Mar 13, 2015 #2


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    Staff: Mentor

    Does this mean you are wanting to wirelessly power some device using a continuous transmission on that RF frequency? Is that allowed under the rules? What are the bandwidth, rolloff and harmonic content regulations for that band?
  4. Mar 14, 2015 #3
    I'll have to understand your reply, thank you for asking the questions.

    Bandwidth. I gather this refers to use of the channel? I can intermittently use the channel, using the RF charging when needed.
    From what I read it, fair use is important, but not enforced. The actual devices will not be around consumers but in large scale industrial projects. I don't know if that is of any importance? I guess I'm suggesting that it will be a distance from people who might want to use this frequency for themselves.

    I'm unsure about rolloff, I guess it's a description of how far the signal travels. I haven't found any limitations on that persay.

    harmonic content, voice transmissions on the set that the frequency, 27.255 MHz is from are not allowed for data transmission and only for one way communication via some kind of audible or inaudible tone.

    The allowance for power transmission is not explicit. But the wording is close to saying any device can operate on this frequency.

    To remove the focus on this particular RF, and to clarify that the wireless transmission will be used internationally (But I focused on USA law because it was the first instance of a non regulated relatively high wattage channel being available for business use) are there any suggestions on how I could approach the general point of this thread?
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