Many thanks to SRAA contributor, Dan Greenall, who shares the following recording and notes:

KC2XIO was an experimental radio station operated by the National Bureau of Standards in Boulder, Colorado between July 1970 and May 1971. This was to gather information in preparation of the format change for WWV and WWVH which happened in July 1971. Here are two recordings of their voice announcement (one male and one female) as heard in Ancaster, Ontario, Canada on a Hallicrafters S-52 receiver that was hooked up to an outdoor longwire antenna. The frequency used for these test transmissions was 13560 kHz shortwave.

Reception location: Ancaster, Ontario, Canada

Receiver and antenna: Hallicrafters S-52 using a longwire antenna