Signal Hound VSG25 - Modification for better frequency stability

Signal Hound VSG25 - Disassembled Signal Hound VSG25 - Modification Closeup Signal Hound VSG25 - Mod Schematic Signal Hound VSG25 - Mod Layout

Tests

Tests run at 162MHz nominal with 0dBm output power. Ambient Temp: 24C Deg

VCTCXO Freq is measured by Racal 2202R Universal Counter/Timer (it has a rubidium reference so it is reliable!)

Frequency drifting before modifications were over 500Hz

Frequency drifting after VCTCXO modification was 19Hz

Initial freq: 162.000006MHz

After 2.5hrs: 162.000025MHz and kept drifting

Frequency drifting after VCTCXO and heatsink added was 10Hz and stabilized relatively quickly

Initial freq: 161.999983MHz

After an hour frequency stabilised on 161.999993MHz