I'm running Stata/SE 15.1 (updated 27/08/19) on MacOS 10.13.5

I would like to convert string data to quarterly dates. I have read and tried to follow much of the advice here:

https://www.statalist.org/forums/for...-date-variable
https://www.statalist.org/forums/for...-to-stata-date
https://www.statalist.org/forums/for...date-variables,

as well as in Chapter 24 and the DateTimeTranslation documentation. None of my attempts are working. I post the simplest of my efforts; I'd appreciate an explanation of my error.

The data:

Code:
* Example generated by -dataex-. To install: ssc install dataex
clear
input str8 quarter_str
"Q12011"
"Q12012"
"Q12013"
"Q12014"
"Q12015"
"Q22011"
"Q22012"
end

My code:

Code:
gen quarter = quarterly(quarter_str, "QY")
The result:

. gen quarter = quarterly(quarter_str, "QY")
(5,280 missing values generated)

I've also tried different formats for the string variable, and adjusted accordingly. e.g.

"Q1/2011"
"Q1/2012"

. gen quarter = quarterly(quarter_str, "Q#Y")

with the same result: an empty variable generated.

Though I'm a regular consumer, this is my first posting to Statalist, and I will be delighted to have my error pointed out in the simplest terms.
Thanks.