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====== Signal Hound VSG25 - Modification for Better Frequency Stability ======

Date: {{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.

{{ :projects:signalhound_vsg25:20240513-121755.jpg?direct | Signal Hound VSG25 PCB and Modification}}
===== 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: =====
{{ :projects:signalhound_vsg25:20240513-122256.png?direct | Schematic}}
{{ :projects:signalhound_vsg25:20240513-124435.png?direct | Layout}}


===== Implementation: =====
{{ :projects:signalhound_vsg25:20240513-121921.jpg?direct |Modification}}


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