This modification is something I came up with after struggling to get a reasonable range from my Nokia N82 to my computer in another room.
The victim was a $8 USB Bluetooth dongle, with a usable range of about 10 metres (less through walls).
Being a radio ham, I am familiar with antennas, and know how critical it is to get the CORRECT antenna length, if your signal is going to be efficient.
I was surprised to find other 'range extender' mods on the net, which did not mention this important fact! (One site had someone who had attached a "foot long piece of wire" onto his USB dongle and was wondering why it didn't work very well!!!)
There is a recognised formula for calculating antenna length/frequency, which is (without going into detail) 300/frequency - i.e. 300/150(MHz) will give you 2 metres.
As Bluetooth devices work at frequencies of around 2450MHz, the formula will give you an antenna length of +/- 12cm.
This figure then has to be divided by 4 to give us a quarter wave antenna, which will be 30mm in length - THIS LENGTH IS CRITICAL!!!
25mm or 35mm will just make it less efficient (Lower range).
Your old CB antenna WILL NOT WORK!
So - if you are happy to try something (at your own risk), and want to get a significant increase in usable range for you dongle, go to the next step, but remember, the end result doesn't look pretty, but performs brilliantly!
Step 1: Opening up the USB Bluetooth device
To get started, we obviously have to get inside the dongle.
The picture shows the dongle with the 'antenna' on the side removed.
Don't worry, this antenna is just a plastic dummy, and performs no function at all!
The plastic case then has to be prised open, using either a flat blade screwdriver, or a blunt knife.
There are no screws.