Airdrop on iMac will not work with iPhone 6

I have an iMac 21 inch, late 2009 running Yosemite. I cannot get my iPhone or iPad to be recognized by Airdrop on my iMac. I read a forum online that said something about the Bluetooth being an older version (0x4 not 0x6). There supposedly is a way to fix this but I don't know how. Any ideas?