TV antenna signal strength is an important metric to measure and know about as it is the single most reliable measurement that tells you how good the visual coming through to your television is. Signal quality is measured in a unit known as Decibel milli-watts. A bad signal is usually around -55 dBm and a good signal is around -75mm dBm. The signal quality is usually measured by the inbuilt devices inside the televisions so you do not need to do this yourself. In case you need to measure the signal coming from the antenna to make sure that it is not damaged, you can do this using a store-bought ammeter. Connect one lead to the antenna and hold the other in your hands, then switch the ammeter to resistance reading mode and it should ideally say 0 ohms. If there is a higher resistance than 1 0hm, this means that the antenna is damaged and needs replacement or repair.