diff --git a/Radio-operation.md b/Radio-operation.md
index 24b1af2..35ff81f 100644
--- a/Radio-operation.md
+++ b/Radio-operation.md
@@ -81,4 +81,25 @@ Menu items for DTMF calling:
 * `D Decd` - turns on the DTMF decoding
 * `D List` - list of DTMF contacts
 
+# Not all original features are available in this firmware.
+
+Because the size of the firmware is limited (60kB), not all functionalities may be available in the firmware. That is why a choice was made so that other functionality could be realized in the radio.
+The menu has also been adjusted as a result. See [Menu](https://github.com/egzumer/uv-k5-firmware-custom/wiki/Menu) for a current description.
+
+The most important differences compared to the original firmware are:
+
+> ENABLE_AIRCOPY        := 0 
+> 
+> ENABLE_NOAA           := 0 
+> 
+> ENABLE_VOICE          := 0 
+> 
+> ENABLE_ALARM          := 0 
+> 
+> ENABLE_TX1750         := 0 
+> 
+> ENABLE_PWRON_PASSWORD := 0 
+
+If you want to change something here, read the **README.md** under [User customization](https://github.com/egzumer/uv-k5-firmware-custom/blob/main/README.md#user-customization).
+