diff --git a/designs/reflectometer_base/reflectometer_tb.sv b/designs/reflectometer_base/reflectometer_tb.sv
index 95abf25..1d1cbd9 100644
--- a/designs/reflectometer_base/reflectometer_tb.sv
+++ b/designs/reflectometer_base/reflectometer_tb.sv
@@ -11,7 +11,7 @@ module reflectometer_tb;
     localparam LOGIC_ZERO_LEVEL     = 0; // DAC -5V for logic zero
     localparam VOLTAGE_ZERO_LEVEL   = 2**(DAC_DATA_WIDTH-1); // DAC 0V for logic zero
     localparam PACK_FACTOR = 1;     // not used in TB
-    localparam PROCESS_MODE = 1;    // 0 - uint, 1 - int
+    localparam PROCESS_MODE = 0;    // 0 - uint, 1 - int. Current accumulator don't support signed sum
     localparam ACCUM_WIDTH = 32;    // accumulator number bit witdth
     localparam N_MAX = 4096;        // max value of windows to average by experiments
     localparam PACKET_SIZE = 1024;  // bytes per UDP packet