A common VCXO specification is the Vc input impedance. A typical value might be 100KOhm or 10MegOhm. What does this actually mean?
Like most oscillators, VCXOs have many specifications. APR – Absolute Pull Range – is a single specification that combines many of them to make selection easy. The term “Pull” is unique to the oscillator industry and refers to the small frequency tuning available via the voltage control pin. Pull is measured as df/fnom in ppm.