When they change systems, the mic frequencies will change too.
The mic system is a part of the actual video recording system.
The digital system is supposed to use a 900 MHz mic, and the receiving antenna is mounted on the charging cradle for the mic which is installed in the car. So they will no longer need an external antenna on the car. The company that sells the recording systems claim they work up to 1000 feet (no typo one-thousand). The transmission is also digital.
Some of the newer VHS systems are already using this digital 900 MHz mic.
As far as the older VHS systems go, the 170 MHz mics are digital encoded, and again are said to work for 1000 feet.