Signal Hound VSG25 - Modification for Better Frequency Stability

Date: 2024-06-01

In this post, I’ll walk you through the modifications I made to the Signal Hound VSG25 to enhance its frequency stability. These modifications included replacing the original 24MHz clock with VCTCXO and adding a heatsink. Below are the details of the tests conducted before and after the modifications.

Test Setup

Frequency: 162MHz nominal
Output Power: 0dBm
Ambient Temperature: 24°C
Measurement Tool: Racal 2202R Universal Counter/Timer (rubidium reference for reliable measurements)

Results Before Modifications

Frequency Drifting: Over 500Hz
Initial Frequency: 162.000006MHz
After 2.5 Hours: 162.000025MHz and continued drifting

Results After VCTCXO Modification

Frequency Drifting: 19Hz
Initial Frequency: 162.000006MHz
After 2.5 Hours: 162.000025MHz and kept drifting

Results After VCTCXO and Heatsink Addition

Frequency Drifting: 10Hz and stabilized relatively quickly
Initial Frequency: 161.999983MHz
After 1 Hour: Stabilized at 161.999993MHz

These modifications significantly improved the frequency stability of the Signal Hound VSG25, reducing the frequency drift and allowing for quicker stabilization.

Schematic and Implementation Below are the schematic and implementation pictures of the modifications:

Schematic:

Implementation:

Feel free to reach out if you have any questions or suggestions for further improvements. Your feedback is always appreciated!

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