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Homebrew passive antenna coupler

Discussion in 'General Electronics Discussion' started by flippineck, Jan 30, 2014.

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  1. flippineck

    flippineck

    320
    13
    Sep 8, 2013
    I have a Sony Xperia phone. As far as I know it works on the 2100MHz band, and the antenna is housed in the bottom part of the phone, widthwise along the base.

    There's no jack on the phone for an external antenna, but I'd like to try connecting one.

    I've come across 'passive coupler' designs many times which seem to consist of a short whip type antenna intended to be mounted on the exterior of a vehicle, connected to a length of coax with I think, some form of induction coil at the other end which you're supposed to place in proximity to the phone. The idea being, that you get some form of inductive coupling between the external antenna and the phone's built-in one.

    Does this approach work and if I was to try a homebrew attempt, what sort of coil etc arrangement would be best at the phone end?

    Being almost completely clueless about V/UHF I would probably just wrap 20 turns of enamelled copper wire round the base of the phone and solder the ends to the coax and see what happened.. but before I do, any suggestions?

    Or are these passive patch type antenna kits all a load of marketing hot air and no theory :confused:
     
  2. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi flippineck,

    I have few doubts about your post, why do you believe that 2100Mhz is used in your phone, are you sure about the bottom antenna location, are you sure about the jack lack (because it's needed for a car kit).

    What's your Xperia phone type ?

    Olivier
     
  3. flippineck

    flippineck

    320
    13
    Sep 8, 2013
    Hi Olivier thanks for responding.

    I'm in the UK and I use 'Three':

    http://blog.three.co.uk/2011/11/25/spectrum-2/

    This is why I'm under belief my 3G phone will be using the 2100MHz frequency.

    It's a Sony Xperia E model C1505.

    I couldn't find an exact document for my phone but I did find teardown links for a very close phone:

    http://www.xperiablog.net/2012/04/30/xperia-s-disassembly-guide/
    http://www.sonymania.cz/storage/1331332888_sb_xperia_s_wi.pdf

    These links are what make me think the antenna is located in the black plastic bar spanning the width of the bottom of the phone.

    There are two jacks on the phone. one power jack, similar to a mini-usb jack (but not quite the same I don't think), and a 3.5mm size 4-terminal headphone jack - which I know does serve as a reception antenna for a builtin FM radio but not, I think, for the cellphone signal)

    I've looked pretty hard both physically on the phone itself, and on google, for a possible 'hidden' antenna jack but haven't succeeded in finding or hearing of one.
     
  4. Y2KEDDIE

    Y2KEDDIE

    259
    15
    Sep 23, 2012
    I bought a cell phone booster amplifier from Wilson. I also bought an inductive pickup/cell phone holder and a second pickup which is Velcro'd to my Verizon computer air card. Both devices deliver 3 signal bars more when attached. There has to be at least one bar of signal to amplify, but it does work well. I toke the inductive coupler/cell phone holder apart, there was just a simple loop inside made from a flexible pc board.
     
  5. shumifan50

    shumifan50

    582
    58
    Jan 16, 2014
    As far as Experia phones are concerned look at this link:
    Passive antenna external is bad

    From what I have seen on the web, the phone will have a connector (the article mentions it as well), so it is a matter of finding the adapter, which might even be a car cradle with an external antenna socket.
     
  6. flippineck

    flippineck

    320
    13
    Sep 8, 2013
    Hiya

    Thanks for the link.

    I'm still looking for any sign of a connector on the phone (maybe one of the pins in the power lead is for an antenna?) but no joy so far.

    The generic patch antenna connector is generally a flattish, squarish sticky thing which does not match up well to the antenna on the Xperia as far as I can tell, so yes, a cradle-type design would probably be more suitable

    What I'm particularly interested in is this line from the link you gave:

    also what Eddie said:

    I'd like to know the parameters, theory etc behind this 'special design' / coil / loop.. so I can try to make something up myself, which i could maybe solder to a length of coax going to a yagi antenna etc.
     
    Last edited: Jan 31, 2014
  7. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Never ear about "three" before, nice learning.

    For the coupling matters look's like Y2KEDDIE provide very handy information's

    cheers,
    Olivier
     
  8. shumifan50

    shumifan50

    582
    58
    Jan 16, 2014
  9. flippineck

    flippineck

    320
    13
    Sep 8, 2013
    hmm pin 4, yes I will look into that :)

    ok looking at the plug on the end of the wall transformer that came with the phone,

    - it's 5 pin
    - it has the USB symbol stamped into the plastic housing of the plug
    - label says "sony model ec450"
    - googling it, it does look very much like micro USB, specifically, micro-B USB.

    would be made up if pin 4 did turn out to be an antenna connection

     
    Last edited: Feb 1, 2014
  10. Paul1966

    Paul1966

    2
    0
    Feb 22, 2020
    Hi All
    sorry to *Bump* this after so long...
    but there has been no resolution posted ?
    @ filippineck did you get/make USB antenna ?
    @ anyone? is this possible ( I use USB C to keep this interesting !!)
    if not is an inductive antenna difficult to make ?
    I would like to do this in conjunction with charging
    either inductive charging pad or USB
    would this be possible ??
    would 2X inductive pads interfere with each other ??

    Thanks in advance
    Paul1966
     
  11. flippineck

    flippineck

    320
    13
    Sep 8, 2013
    Sorry to say, I never took this any further & no longer have the phone
     
    Paul1966 likes this.
  12. Paul1966

    Paul1966

    2
    0
    Feb 22, 2020
    Hi flippineck,
    thanks for the quick reply !
    sorry to 'hijack' your thread, sad you didn't take this further...
    but not really surprised you no longer have the phone ;)

    TBH I thought this would be quite a common mod/hack,
    I live less than 50 miles from London & my daily commute
    (20 miles toward london into another city !!)
    takes me through 2X 'dead spots' on an A road !!
    I can't be alone.. can I ??

    thanks in advance for any input
    Paul1966
     
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