They only need to maintain the property in the condition in which you leased it.

So if the TV aerial was working when you rented the place and now there is a physical issue with it, then they must fix it.
If you caused the problem (kicked the footy on the roof and knocked the aerial off) then it is your responsibility.
If it wasn't working when you moved in (ie you didnt tell them it wasn't functioning as per condition report as soon as you moved in) then it is your issue to deal with.

From personal experience, check all your connections and your tv cable, it can often be damaged and you may not know Replace the connections and the cable and see if it makes a difference.