diff --git a/pyat/ram.py b/pyat/ram.py
index d122b84..32c436f 100755
--- a/pyat/ram.py
+++ b/pyat/ram.py
@@ -23,8 +23,8 @@ def call_ram(freq, sd, bathm, ssp, sed, dr=0.1):
     rmax = max(bathm.r)             # Maximum receiving range (unit: m)
     zmax = round(max(bathm.d) * 2)  # Maximum receiving depth (uint: m)
     zmplt = round(max(bathm.d)*1.1)     # Maximum depth of plot (uint: m)
-    dz = 1500 / freq / 15           # Step in depth direction: wavelength / 15
-    dr = 1000* dz                     # Step in range direction
+    dz = 10          # Step in depth direction: wavelength / 15
+    dr = 1000* dr                     # Step in range direction
     Zmax = calZmax(ssp, sed)
     rd = Zmax
     pos = PosRAM(sd, rd, rmax, zmax, dr, dz, zmplt)