Alternating dash lengths within a dashed line

Hi, I am brand-new to Illustrator and hoping there is an easy answer to this. I've looked at several videos, but I can't find anything that explains exactly what I need.

I'm trying to create a dashed line with alternating dash lengths. I've been playing with the "dash" and "gap" fields in the stroke options but can't figure out how to make the dashes uniform, where every other dash is long, and every other one short, with the same gap for each. I want it to look something like this (I didn't create the image below) -

How would I create a dashed line like this? Thanks in advance!