diff --git a/README b/README
index 4e6286c..883156d 100644
--- a/README
+++ b/README
@@ -7,6 +7,9 @@ port to Antenna (and LPF), operates on LF, MF, HF and VHF bands from
 Compatible with the original Raspberry Pi, the Raspberry Pi 2/3, and
 the Pi Zero.
 
+This version uses https://github.com/F5OEO/librpitx
+**You need to add gpu_freq=250 in /boot/config.txt. Without that transmiting is unstable"
+
 
 ******
 Installation / update: