RN-41 BT module _very_ short on range

Discussion in 'Embedded Systems and Microcontrollers' started by aeroguy, Oct 18, 2012.

  1. aeroguy

    Thread Starter Member

    Sep 16, 2009
    40
    2
    Hello,

    I did some development work on my breadboard using an RN-41 BT breakout from sparkfun. It worked really well, and at great distances on my breadboard.

    Later, I developed and fabricated a PCB for the same circuit, and integrated an RN-41 module into it. Unfortunately, the range that I can transmit from my PCB is very short/weak - about 10 feet or so instead of 100+..

    I verified that the RN-41 is set to transmit in it's highest power mode, but I don't think that is the problem. I feel that there is a hardware issue of some kind.

    I do have a little bit of metal beneath the antenna on my PCB, in the form of my name, and a single trace passing by. It would surprise me if this was the problem, since my range limitation is so profound.

    There are pads on the underside of the module that are supposed to be grounded per the data sheet, but research I did on this indicated that people generally don't connect those. Thus, I didn't connect them.

    I've attached an image of both sides of my board, plus a schematic of the RN-41 connections. I sketched in the placement of the RN-41 in red, and depicted its antenna in blue. The RN-41 pads not shown as connected in the schematic are sitting on pads, but not soldered to them.

    If anyone has any thoughts or experience on this matter, I'd really appreciate any suggestions.

    Kind regards,
    Eric

    PS - perhaps I should have put this thread in the RF forum..?
     
    Last edited: Oct 18, 2012
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    As bluetooth is working in the 2.4 Ghz range, anything that is closeby the antenna will interfere.
    It could indeed be that the single trace going under the antenna is giving the trouble.
    Is there a free space (around the antenna) given in the datasheet of the module?

    Bertus
     
  3. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    Looking in the datasheet, there must be a free space around the antenna part of the module:

    [​IMG]

    Bertus

    PS the complete datasheet is also attached
     
  4. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,395
    1,607
    Can you make an extension cable to place the RN-41 a distance away from your PCB?
     
  5. aeroguy

    Thread Starter Member

    Sep 16, 2009
    40
    2
    I guess maybe that is my problem.

    This may be one of those times when intuition can lead a person astray. To the uneducated (me) it seems so hard to believe a little trace and a couple of copper letters under the antenna can render it virtually useless! It is very easy to believe that the range would be reduced some, but for practical purposes it basically went to zero.

    I'd like to remove the module from this board and "edit" the board to remove those traces, then reinstall for experimental purposes. Without a hot air station though, it may be tricky.. I'll have to ponder that a bit.

    Your feedback and effort is appreciated, as always.

    Thanks!
     
    Last edited: Oct 19, 2012
  6. aeroguy

    Thread Starter Member

    Sep 16, 2009
    40
    2
    I could have done something like that if I'd planned for it from the beginning. This one is surface mounted. For space savings, I'd like to figure out how to get this to work "on board" for my next iteration, since it should be doable.

    thanks!
     
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