"Yours Truly" checking the antenna tuning unit (ATU) prior to the day's transmissions. The box contains a simple T-network for matching the 66 ohm impedance of the tower to the 50 ohm output impedance of the transmitter while tuning out the reactive component of the tower. The antenna base current was constantly monitored while WP3XEN was on the air. The round window in the door of the ATU allowed me to view the base current meter and the CCTV camera fed a picture of the meter to a monitor in the construction trailer.

ATU closeup

Another view of the ATU door, showing the base current meter a few minutes before the day's scheduled transmissions.