What is the effect of ice on an antenna?

Question

A local FM radio station transmitting at 89.3 MHz recently announced that it would be running at 50% power due to freezing weather and a forecast of ice accumulation, as "when ice is forecast ... it can damage our antenna if we run at full power."

What is the effect of ice on (the electrical properties of) an antenna?

Answer 1

Ice, like water, has a much higher dielectric constant than air. This can detune the resonant frequency of the antenna so there is now an impedance mismatch with the feedline (transmission line feeding the antenna) at the frequency you're using. This is manifested as an increase in VSWR (voltage standing wave ratio). Basically this means that, since more power is being reflected from the antenna back into the feedline, you need to have a higher power in the feedline to get the same radiated power.

See the second question here: http://www.michwave.com/bbnetwork/faq/troubleshooting.htm