Increasing the range of 343MHz Rx TX

Discussion in 'The Projects Forum' started by jimit, Jan 4, 2012.

  1. jimit

    Thread Starter Member

    Oct 28, 2010
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    0
    Hi every one :p
    I have made a rf car which works at 434 MHz
    the transmitter works on 9v and the receiver works on 5v.
    the range of this is about 5 feet
    and according to the kit it should go up to 100 feet
    actually it is a spy car it also has a wireless cam on it so i need more rang for it to work
    my question is can i increase the rang of it and if yes then how?????
    this kit had a p rebuild 343 MHz Rx TX module
    and i am using a 7cm ant for this
    i found that we can use some transistor for boosting the range (after some googling) but how???
    thx in advance :):)
     
    Last edited: Jan 5, 2012
  2. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    If the range is THAT low there is probably something wrong with your antenna configuration. First of all, a quarter wavelength monopole would be 21.85cm long, how does 7cm fit in there?

    Did you use 7cm on receiver and transmitter side?

    What model is the kit you used?

    Post pictures, schematics and datasheets.
     
  3. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    Once you get it to normal working range (either no antenna or bad device right now), install a highly directional antenna on both ends if possible. Look at a Yagi design a "dish" would be way to big for this wavelength.

    A big boost will be found if both of your antennas are in the same plane/polarization. Such as both vertical or both horizontal. Having one vertical and one Horizontal will cut the signal down a lot, 6-9dB or more depending on antenna type.
     
  4. jimit

    Thread Starter Member

    Oct 28, 2010
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    0
    this is the pdf copy given with the kit.
    and this is the PCB.
    I have used a vertical ant on both RX and TX.
    and also have changed the length of it to 21 cm but not much difference.
     
  5. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    Ok. That's 434MHz, so a quarter wavelength is 17cm.

    You did try the whip antenna I presume?

    5 feet is really not enough. The datasheet specs normally give the transmitting/receiving distance for line-of-sight. Did you test this through walls or with no obstacle between the two devices?

    Last but not least, the signal you can receive indoor varies greatly due to reflections.
    Have a look at this simulation:
    [​IMG]

    However, these RF modules are normally quite easy to use since antenna impedance matching LC networks etc are already integrated...
     
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  6. jimit

    Thread Starter Member

    Oct 28, 2010
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    I am sorry its 434MHz not 343MHz got confused sorry once again. :p
     
  7. jimit

    Thread Starter Member

    Oct 28, 2010
    57
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    yes i have tried it between walls and other obstacle it does work but not always....
    no i have not tried a whip antenna actually i am new to antenna
     
  8. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    Can you post high resolution, clear/well focused pictures of the board after you assembled it (both sides)?

    Max .JPG size is 300kB, and it may take a few minutes to have the attachment moderated, but that will help us determine if there are problems with the transmitter and receiver itself.

    If you don't have a camera, use a flatbed scanner to get the images.

    Download Irfanview (freeware) which will allow you to "Save For Web" with the R|0T plugin and specify size to be 300k, it does a good job of keeping the high resolution while getting good compression.
     
  9. jimit

    Thread Starter Member

    Oct 28, 2010
    57
    0
    Is it necessary to have the same length of antenna on both RX and TX ??????
     
  10. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    For a quarter wavelength antenna, try a straight wire 6.5" long on each side.

    For a half wavelength antenna, it would be 13" on each end, which may not fit too well with the "spy" part.

    Use the longest antenna possible, so maybe half wavelength on the receiver/non-moving portion, and the 6.5" on the moving portion.

    It would help if you can get the antenna mounted over a ground plane, which is 4 to 12 pieces of 1/4 wavelength (6.5") wire connected to ground, going North, South, East, West from the base of the antenna, with the antenna sticking straight up from where all 4 ground wires meet. Try to make at least a 3-4" "diameter" (imagine circle made from the 4 horizontal wires being 2 perpendicular diameters) ground plane, the circuit board may have ground cladding beneath the antenna, range will be greatest in the direction with the most ground plane. This is probably not possible on the receiver side, so try to get at least 2" of "ground" around the other end. For the ground plane, more is better, and some is better than none.

    Bad TeX rendition: \stackrel\mid\bigoplus The vertical line sticking up is the antenna, the + in the middle are the 4 ground plane wires, and the circle is the imaginary ground plane. It can be split up to 8 wires or more to a complete halfwave circle if desired.

    The ground plane is why many police car antennas are mounted in the center of the roof instead of the edge, at least 1/4 wavelength from an edge, and the RF tends to be directed in the direction with the most ground plane.
     
    Last edited: Jan 5, 2012
    jimit likes this.
  11. DickCappels

    Moderator

    Aug 21, 2008
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    Since this was a kit, there is a very good chance that it was not assembled properly, not adjusted properly, or might even have incorrect parts in it.

    Could it be your receiver? Did you tune your receiver according to instructions?
    Most likely it is a regenerative receiver (a good one would have a preamp to isolate the regenerative detector from the antenna), and being a regenerative receiver, it probably needs to be tuned to the transmitter's frequency.

    Another thing to check is that the transmitter's frequency determining element (most likely a SAW device) is of the correct frequency -I repaired an RC car with a similar problem last year -the transmitter was crystal controlled at 35 MHz while the receiver was tuned to 27 Mhz -range was pretty poor until I put the transmitter on the receiver's frequency.
     
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  12. jimit

    Thread Starter Member

    Oct 28, 2010
    57
    0
    thx to all but i have fixed the prob
    i just connected a loop antenna to the RX and got upto 133feet of range :p
    thx again...........:)
     
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