It's digital TV there (so don't bother getting an analogue stick). Get a good quality one as well - they tend to last longer (my initial cheap one failed after a few weeks). The small aerial you get with them is sufficient (generally is not in the UK) as the signal is strong. Try getting one from Amazon direct (not through one of the Amazon resellers) as you can then send it back if it fails through BFPO.
How do I watch BFBS TV?
BFBS TV in Afghanistan is via DTT in the main areas of Helmand Province. This means you can take your own TV with you and watch it in your own bedspace - you'll just need to take a 'Freeview' box and of course an external aerial. Most new TVs have an integral digital tuner, so you won't even need a Freeview box, just an aerial. If you are taking a laptop, a USB stick (such as Freecom) to let you watch DTT on your laptop costs around Â£35. This will also require an external aerial and co-axial cable. If it's too late for you to buy before you go, all these items are available on the internet from websites like Amazon, who will post to BFPO addresses, and are under the 2kg BFPO limit. Make sure you follow their BFPO address guidelines.
Is DTT everywhere in Afghanistan?
DTT is available at Kandahar Airfield, Camp Bastion, Lashkar Gar and Gereshk. At smaller FBs there is more likely to be a communal TV fed directly from a satellite dish. Further forward at small patrol bases there may be no TV at all. Elsewhere in Afghanistan, reception is via cable or DTH. There's a cable system in Camp Souter, so you plug your own TV into the socket in your accommodation. Elsewhere in Kabul it's DTH to communal TVs.