Applicable to SU/RB and to AU/BU.
Not applicable to SU/RB with SW version 4.0 and higher.
Applicable to all units with HW revision B and lower
(for units with HW revision C and higher replaced by
brzaccVLFrequencySubsetFrequencyNew to support a
resolution of 0.5 MHz).
The frequency in MHz of an entry in the Frequency Subset table.