One alleged reason for the stainless steel, fixed length masts was how easily a telescoping mast antenna could be destroyed on the streets of NYC, by people "walking around". A quick karate chop and it's history. With a fixed mast (if they didn't notice it first!), that same "chop" could result in a bent mast that rebounded to smack its attacker. Not to mention how the edge of the attacker's handle felt.
It was always easy to tell the people who lived/worked in the boondocks, as they'd run the telescoping antenna mast all the way up. Which then meant that highway speeds (and any tree branches) would give it an arc toward the rear of the car. Car was usually not recently-washed either. To me, the stainless steel mast was the best compromise, for many reasons.
The progression was: normal, round telescoping antenna masts. then the tear-drop shaped (at least the bottom two sections) telescoping masts for less noise, and then the 31" stainless steel fixed masts. At a time when GM (and Chrysler Imperials) were trying to make "windshield antennas" work better. As power antennas were a luxury option.
Enjoy!
CBODY67
