Aerials are quite simple things so fixing a broken aerial is often a DIY task.
Understanding your aerial
Whether it is a car radio or a tv receiver, the aerial works in a simple way. The metal rods or dishes catch radio waves.
The radio waves flow through the metal antenna and cause the electrons within it to vibrate, generating a very small electrical current carrying a replica of the original signal. This is then boosted (amplified) and sent to speakers (in the case of analog) or decoded (digital) and then turned into audio or visual data.
Therefore the major problems occur when the connection between the aerial and the rest of the receiver is broken.
You may find that simply wedging the aerial a little more tightly into its socket is all you need. Another trick is to drop a steel needle into the aerial socket to improve the connection. (Don’t try this on a mains powered receiver without serous precautions against electrocution).
Fixing an AM aerial
AM signals require an aerial that is very long (we are talking 1000metres plus), but luckily we can wrap a km of thin copper wire around a ferrite metal core and stuff it inside the body of the radio itself. So, if your AM signal fails, open the radio and check that the ends of the copper coil are attached to the circuit board. If not, they can be soldered back in place.
Broken arm on a TV aerial
Glue it back in place using ‘wire glue’ (electrically conductive adhesive) and you should see an immediate improvement in signal quality.
Repairing Satelite Dishes
Firstly, it may simply be that a storm, snow or torrential rain has slightly moved your dish so you are no longer pointing at a satellite. If this is the case you can try realigning yourself, but it is probably easier to call out a repairman who has a realignment tool.
If your parabolic dish is cracked, a bit of superglue should be fine. The Parabolic dish justs reflects the signal, focusing it onto the the little receiver (LNB) so the glue shouldn’t cause you problems. If the LNB is playing up, you can replace it without swapping the reflector. Maplins do them really cheaply. The one thing you should not skimp on is the quality of the coaxial cable that leads from the LNB to your sky/freesat box. Good quality outdoor grade coaxial will serve you well for many years.