The radio must be using a system type that enables the extensions. This can be done on a per-mode basis in the radio. The SCGAR, scgar, HQ, HQII and HQIIA system types permit the use of the extensions. The extension values are driven by a host computer or dll running on the DACS.

Hint: When going into Frequency Hopping (FH) mode and enabling the extensions many users also switch from mulaw to CVSD as a voice encoding scheme. This roughens up the audio between FH and non FH modes of operation.

For Model Builder versions prior to 4.06 the extensions were only used when in SCGAR mode and scgar.

MB is aware of the system type being used so that a HQ radio will not talk to a SINCGARS radio if they happen to use the same extension values.