This is a 720k disk image.  You need Teledisk to recreate the disk.
Teledisk can be found at:

    ftp://tvdog.shacknet.nu/tandy1000/system/teled212.zip

The disk should be labelled:

Msdos.td0      MS-DOS/GW-Basic 3.2.21

Tandy DOS 3.2 is usable on other 1000-series models (it will not 
run on a non-Tandy machine).
