The 207-5 VLF Receiver/Comparator with internal standard and comparator provides frequency coverage of 8.0kHz to 31.9kHz in steps of 100Hz with an additional 60kHz channel. Short and long term stability is ±0.5 µs. Under laboratory conditions intrinsic calibration accuracy (relative to received VLF carrier) is ±1x10E-11 per 24 hours. Receiver sensitivity is 10 nV signal at 50-ohms antenna input terminal. A built-in recorder on the front-panel records a time history of the accumulated phase difference between the local standard and VLF carrier, up to 9999.9 µs. Internal standard is 1MHz with 24 hour stability of ±2x10E-09 (after one month)