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Adjust the range of Transmitter

Discussion in 'General Electronics Discussion' started by Einstein Jr., Oct 21, 2014.

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  1. Einstein Jr.

    Einstein Jr.

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    Oct 21, 2014
    Hello, everyone! Does anyone know how one would be able to use a variable capacitor or potentiometer or something of that nature to adjust the range of an FM transmitter. Attached is the circuit.
     
  2. Arouse1973

    Arouse1973 Adam

    5,165
    1,087
    Dec 18, 2013
    Hello
    There is no attachment. Increasing the range of the transmitter would normally involve either increasing the power of the transmitter of the sensitivity of the receiver. Increasing the transmitted power might cause you to be transmitting illegally, dependant on what the laws in your country allow. you have to be very careful doing this, and increasing the receiver sensitivity may not be as easy as it sounds. What frequency are you transmitting and what distance are you after. Just using a better receive antenna maybe all you need.
    Thanks
    Adam
     
  3. Einstein Jr.

    Einstein Jr.

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    Oct 21, 2014
    Yea, I just wanted to be able to adjust it from my transmitter in the event that I dont want people in 20 houses down hearing my transmissions. But sometimes I do so I would like to somehow build an adjustable range into the circuit.
     

    Attached Files:

  4. Gryd3

    Gryd3

    4,098
    875
    Jun 25, 2014
    I think we all thought you wanted to 'extend' it, not reduce it.
    If you are tinkering with the transmitter, it should be easy enough to add a potentiometer to reduce signal strength.

    I can't give you any detailed tips though, as I am not familiar with radio enough to tell you if simply adding a potentiometer will do any good. My current understanding is that you will most likely need a logarithmic potentiometer if my proposed solution is a valid one.
     
  5. Bluejets

    Bluejets

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    Oct 5, 2014
    Maybe put it inside a fruit tin, lift the tin up to adjust range...o_O
     
    Einstein Jr. and davenn like this.
  6. davenn

    davenn Moderator

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    Sep 5, 2009

    there's no easy way to do that

    Bluejets suggestion is funny but in your case isn't a bad suggestion

    Dave
     
  7. hevans1944

    hevans1944 Hop - AC8NS

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    Jun 21, 2012
    There really is no way to control the range of a radio transmitter, except perhaps by changing the transmitter power. Even lowering the power is no guarantee that the range will be reduced. Range depends on a lot of factors and how you define "receive". Voice modulated FM (your circuit) will have a range that is very much dependent on the receiver. Try taking a portable FM radio out into the country to see what effect range has on your reception. Anyway, to decrease range you might try using less than 9 V to power it. It might even work with a single 1.5 V dry-cell.

    I also like @Bluejets idea of placing it inside a can and lifting the can to adjust range.

    What are you going to use this for? Will your neighbors tell you if they "overhear" conversations you are "broadcasting" on the commercial FM radio band?
     
  8. Einstein Jr.

    Einstein Jr.

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    0
    Oct 21, 2014
    Ok well maybe the range cannot be adjusted without a fruit can ;). I thought that I had never heard of it but decided I would look around - ok well thanks for the information everybody.
     
  9. hevans1944

    hevans1944 Hop - AC8NS

    4,595
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    Jun 21, 2012
    The fruit can is just one way to easily adjust the radiated power to limit the effective range. Radio signals propagate.
     
  10. Arouse1973

    Arouse1973 Adam

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    Dec 18, 2013
    Oh I thought you wanted also wanted to increase the range sorry it's just what most people want to do. You can easily reduce the range by adding an attenuator on the output. Fit your PCB into a simple metal enclosure with a BNC connector on the outside so you can add your own different size antennas if you want. The attenuator could be a BNC 50R attenuator but your going to have to match your transmitters output to 50R first for a known transmission performance / output power . Because your circuit is low power, a simple potential divider or maybe a resistor T or PI attenuator before the BNC connector might be all that's needed to reduce the output.
    Thanks
    Adam
     
    Last edited: Oct 22, 2014
  11. Electro132

    Electro132

    261
    3
    Feb 12, 2013
    There is a way to increase the range and that depends on how far you want to go. For e.g. Satellite Communications or FM Radio.
     
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