Electronic – adding a yagi antenna to a bluetooth dongle

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I want to set up a Bluetooth link between devices that are over 2000 feet apart. Yagi antennas for 2.4GHz that can connect to routers are available. A cheap Bluetooth dongle that can be easily taken apart can be found on DealExtreme (see the insides of one at http://we.easyelectronics.ru/Stress/prikruchivanie-usb-ustroystva-k-vnutrennostyam-noutbuka.html [In Russian] ). The cheap Bluetooth dongle has an antenna on its PCB. How can the internal antenna, with its single wire connection, be disabled and the external Yagi, with its coax wiring, be connected for strong signal strength?

This is an example of the type of dongle I'd like to modify. The antenna trace can be seen on the right side of the PCB.

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Best Answer

A Yagi antenna for bluetooth may increase your gain. Keep in mind that Yagi antennas are directional antennas so if you move your target around you will have to move your antenna.

In order to use an external antenna, you would have to take following into consideration:

  1. Use a coaxial cable with the same impedance as your antenna and your final amplifier at bluetooth end.
  2. Cut the trace on the PCB that acts as an antenna
  3. Try o match the feed point impedance and the impedance at source by minimally separating the coaxial conductors (center and shield) at either end.
  4. Make sure you account for signal loss in the co-axial cable. Use a better cable if you want to reduce the loss.
  5. There could be more points to consider apart from the ones above
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