Fig. 4 summarizes the measured peak or operating frequencies (fig. 3a) of the four generators at different power settings.
The data represent the averages of six measurements done every other month for a period of one year.
The standard deviation shows the frequency shift of each generator in one year.
Generators had varying operating frequency typically within 1-2 MHz over one year for a specific power setting.
Considering the 2-10 kW possible power setting for generators 1 and 2, the operating frequency bandwidth of generators 1 and 2 was 908-914 MHz and 912-919 MHz, respectively.
In comparison, generators 3 and 4 had relatively consistent operating frequency (