In some aircraft there is an updated version of the AN/ARC-513 (Figure 1-10-17). This VHF/FM is essentially the same as the original version, with the following minor differences:

a. Manual Tone Switch Selections. ON/OFF/MAN TONE. Since the radio does not have a tone generator embodied in its design, this switch will have no effect on radio function. Switch can be left in any position, however, it is recommended that it be left in the OFF position.

b. Photo Resistor. On the upper right hand corner of the control panel is a photo resistor. This device will automatically dim the frequency read-out LED display and the MAIN, GUARD and XMTR lights during reduced lighting conditions.

c. CHANNEL Selector. To further simplify control function, the CHANNEL selector has been rotated CCW 90 degrees to the 9 o’clock position.

d. PRESET RX/TX Switch. When the radio is turned on, the frequency read-out LED display will not automatically illuminate. To illuminate LED display, select RX or TX on PRESET and the frequency read-out LED display will illuminate.

e. XMTR MAIN/GUARD Switch. The two functions performed by the switch have not been altered, however, the switch selections are opposite to the original version.