What resolutions does the StarTech.com ST122UTPA support at various distances?

The StarTech.com ST122UTPA supports 1440x900 at 150 feet, 1280x1024 at 300 feet, and 1024x768 at 500 feet.

What is the maximum distance this VGA video extender can transmit signals?

The maximum distance this VGA video extender can transmit signals is up to 500 feet (150 meters).

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StarTech.com ST122UTPA VGA Video Extender over Cat 5 with Audio - Up to 500ft (150m) - VGA over Cat5 Extender - 1 Local and 1 Remote

Extend and distribute a VGA signal and the accompanying audio to a remote display over Cat5 cable
1440 x 900 @ 150ft. / 50m
1280 x 1024 @ 300ft. / 100m
1024 x 768 @ 500ft. / 150m
VGA Extender
VGA over Cat5
VGA Monitor Extender
VGA to Cat 5
External
Up to 490 ft.