What size antenna for 35MHz?

Discussion in 'General Electronics Chat' started by Little Ghostman, May 3, 2014.

  1. Little Ghostman

    Thread Starter Member

    Jan 1, 2014
    294
    97
    Hi
    I have finally found the radio controller for my helicopter, however the antenna is missing, I need to do some test for a short period, would it be ok to use a temporary antenna (bit of wire) for a temporary antenna?
    The other question of course is how long should it be for 35MHz?
    I am going to use the joysticks from this controller to make a hand held one, but before I start stripping it down I want to get some measurements from the current set up on the helicopter.
    The new controller will operate around 868 MHz, so it's a bit pointless buying a antenna for 35 MHz, I may even use the complete controller and just add my own electronics to it and switches etc, I also intend to have a ground control station, there will be a key switch that chooses which of the controller has control. Finally feels like I can make some progress!
     
  2. Brevor

    Active Member

    Apr 9, 2011
    279
    54
    The formula is 300/freq. in Mhz, or 300/35. this is the wavelength in meters. for a quarter wave antenna you would then divide the result (8.57) by 4. Finally you multiply that number by .95 to account for the velocity factor. So the final length would be very close to 2 meters. (2.0357)
     
  3. Little Ghostman

    Thread Starter Member

    Jan 1, 2014
    294
    97
    Thank you, I did google it but I doubted my calculation, and I was correct to doubt it! Somehow I got it wrong :(, the page I found didnt mention the .95.
    I have a radio antenna that I have no idea what its from, but its extendable (one of those portable radio skinny antenna's for fm radio), I might give this a try now I know the correct length, the new transceiver has a rubber duck stubby antenna I can use for 868MHz.
     
  4. Brevor

    Active Member

    Apr 9, 2011
    279
    54
    The .95 (velocity factor) isnt all that important unless your a perfectionist. It's because the electromagnetic energy moves slightly slower through a conductor than it does through free space.
     
  5. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    just as cb walkie talkie atennas arent 8 ft long, the antenna is probably shorter for your transmtter. if you have a shop with that brand transmitter there, measure the antenna. there is an internal loading circuit to compensate for the length that will have to be adjusted if it is changed mucn.
     
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