Before the ATU can be used for an application, it must be connected to an antenna to "learn" its characteristic. Learning takes place in a user-defined frequency range in the HF band (1.5 MHz to 30 MHz).
The ATU "learns" the antenna characteristic by receiving tuning data for a maximum of 1500 predefi ned frequencies. Once the tuning data for these frequencies is known and stored, the typical ATU setting time to these channels is less than 5 ms.
Repeated tuningA change in environmental conditions may slightly alter the actual antenna tuning data as compared to the stored data.
The quality of antenna matching is therefore checked during operation by means of an integrated VSWR measuring device. If the required VSWR (<1.5:1) is not attained, the ATU can be retuned in less than (typ.) 100 ms.
The advantage for the user is low probability of intercept (LPI), since ATU frequency setting is performed very quickly and without any emission of RF power.