diff --git a/simulations/airshower_beacon_simulation/aa_generate_beacon.py b/simulations/airshower_beacon_simulation/aa_generate_beacon.py
index b932649..132fe03 100755
--- a/simulations/airshower_beacon_simulation/aa_generate_beacon.py
+++ b/simulations/airshower_beacon_simulation/aa_generate_beacon.py
@@ -306,16 +306,18 @@ if __name__ == "__main__":
         if False: # modify trace lengths
             N_samples = len(antenna.t)
             new_N = 2*N_samples
+            new_N = 10000 # ns = 10us
+            pre_N = 2000 # ns = 2us
 
             dt = antenna.t[1] - antenna.t[0]
-            new_t = np.arange(0, new_N)*dt + antenna.t[0]
+            new_t = np.arange(-pre_N, new_N - pre_N)*dt + antenna.t[0]
 
             antenna.t = new_t
 
             # TODO:trace extrapolation?
-            antenna.Ex = np.pad(antenna.Ex, (0, new_N-N_samples), mode='constant', constant_values=0)
-            antenna.Ey = np.pad(antenna.Ey, (0, new_N-N_samples), mode='constant', constant_values=0)
-            antenna.Ez = np.pad(antenna.Ez, (0, new_N-N_samples), mode='constant', constant_values=0)
+            antenna.Ex = np.pad(antenna.Ex, (pre_N, new_N-N_samples-pre_N), mode='constant', constant_values=0)
+            antenna.Ey = np.pad(antenna.Ey, (pre_N, new_N-N_samples-pre_N), mode='constant', constant_values=0)
+            antenna.Ez = np.pad(antenna.Ez, (pre_N, new_N-N_samples-pre_N), mode='constant', constant_values=0)
 
         t0 = 0
         c_light = 3e8*1e-9 # m/ns