diff --git a/tnc/modem.py b/tnc/modem.py
index 3acf6d13..ae8db8b8 100644
--- a/tnc/modem.py
+++ b/tnc/modem.py
@@ -1251,11 +1251,11 @@ class RF:
                         range_end = range[1]
                         # define the area, we are detecting busy state
                         #dfft = dfft[120:176] if TNC.low_bandwidth_mode else dfft[65:231]
-                        dfft = dfft[range_start:range_end]
+                        slotdfft = dfft[range_start:range_end]
                         # Check for signals higher than average by checking for "100"
                         # If we have a signal, increment our channel_busy delay counter
                         # so we have a smoother state toggle
-                        if np.sum(dfft[dfft > avg + 15]) >= 400 and not TNC.transmitting:
+                        if np.sum(slotdfft[slotdfft > avg + 15]) >= 400 and not TNC.transmitting:
                             ModemParam.channel_busy = True
                             ModemParam.channel_busy_slot[slot] = True
                             # Limit delay counter to a maximum of 200. The higher this value,