How can I tell if my FM/AM aerial is amplified?

Unamplified

Your FM/AM aerial is almost certainly unamplified (also called passive) if it is any ONE or more of these:

Longer than 60cm
Telescopic
Fully Retractable
Electrically powered up/down

Amplified

Your FM/AM aerial is almost certainly amplified (also called active) if it is/has any ONE or more of these:

Built-in-the-glass
‘Beesting’ type
Shorter than 50cm
A spiral outer
A power supply cable

By Test

Test #1) Disconnect the aerial from the radio. Set a multimeter to its lowest resistance range. Measure the resistance between the aerial element /mast and the centre pin of the plug that in the back of the radio. If it measures less than a couple of ohms the aerial is probably unamplified (also called passive).

Test #2) Disconnect the aerial from the radio. Set a multimeter to its highest resistance range (200M or more). Measure the resistance between the aerial element/mast and earth (be  certain not to touch the metal of either probe with your fingers). If the measurement is anything other than open circuit the aerial is probably amplified (also called active).

Still Unsure?

If you remain unsure and the aerial is factory-fitted, please ask the vehicle manufacturer or dealer. If they don’t know, no-one does!

How To Bypass An Existing Aerial Amplifier

Please see here.