diff --git a/NOTES.txt b/NOTES.txt
index 34a67f8..4a8fd36 100644
--- a/NOTES.txt
+++ b/NOTES.txt
@@ -171,4 +171,11 @@ radio538   102100000  (medium)
 radio10    103800000  (bad)
 radio west  89300000  (medium)
 
+
+Stereo pilot frequency
+----------------------
+
+radio3 19 kHz pilot = 18999.8 Hz +- 0.05 Hz
+(5 hour measurement of pilot vs internet NTP)
+
 --