For SSB operation the 36 MHz signal is mixed down to 6 MHz. This 6 MHz signal is again feet into a phase comparator where it is compared to the signal of the 6 MHz VFO. This way the stable 6 MHz VFO is able to control the 36 MHz VFO which again is able to control the 96 MHz VFO. A well designed 6 MHz VFO is by far good enough for SSB, so the 96 MHz VFO in this system is good enough too. (For experts: since the time constant of the PLL loop filter is quite large, the phase noise of the 96 MHz VFO is significantly reduced also.) The frequency range of the 6 MHz oscillator is only 500 kHz, but this is completely sufficient since all SSB/CW operation is located in the 144 – MHz area.