Airdrop on iMac mid-2011 not seeing iOS or OSX devices

I have a mid 2011 iMac running Yosemite that does not show any Airdrop options.

My other devices are iPhones 5 & 5S, iPad Air and a MacBook Pro mid 2012 all running most current OS.

The other devices all see each other on airdrop, but none see the iMac and the iMac doesn't see the others. I have run through a couple online lists of things that could be wrong and it still does not work. WiFi and Bluetooth are on for all devices and the Firewall on the iMac is not set to "block all incoming connections".

Any help would be appreciated.