Richard Allen, reporting via Glenn Hauser's DX Listening Digest, is reporting the experimental test station on the air from Chilocco, Oklahoma. This is on the state's northern border, near Arkansas City, Kansas and roughly midway between Wichita and Stillwater.
1kHz test tones have been reported on 540 and 830kHz. The station is also authorized to use 1680, as well as 92.3, 99.1, and 107.5 FM.
For more information see previous DXLD items on:
It should be noted tests are also authorized (on different frequencies) from Flying H, New Mexico, near Roswell.
Previous similar tests seem to have been in connection with portable temporary stations for the military.