[Tom] used a Teensy 3.1 Arduino compatible board ... The VCXO means voltage controlled crystal oscillator. The crystal is 25 MHz and provides a very stable frequency source for the chip.

The oscillator in the setup and shown in Figure 1 is just a pair of 2N3904s, a 10 µH inductor, a 2.6 nF capacitor, and a 1K bias resistor operating from -2 V. This produces a ~1 MHz oscillator output.

Abracon has released several new lines of MEMs oscillators for the electronics market. The company’s portfolio now includes over 1,700 distinct part numbers designed to address specific requirements ...