diff --git a/amodem/config.py b/amodem/config.py
index c356fe3..1cf7b54 100644
--- a/amodem/config.py
+++ b/amodem/config.py
@@ -1,15 +1,24 @@
-import numpy as np
-
-## Parameters
 Fs = 32000.0  # sampling frequency [Hz]
-Nfreq = 8  # number of frequencies used
 Tsym = 0.001  # symbol duration [seconds]
+Nfreq = 8     # number of frequencies used
 Nx = 8
 Ny = 8
+F0 = 1e3
+
+# Update default configuration from environment variables
+settings = {k: v for k, v in locals().items() if not k.startswith('_')}
+
+import os
+for k in settings.keys():
+    v = settings[k]
+    settings[k] = type(v)(os.environ.get(k, v))
+locals().update(settings)
+
+import numpy as np
 
 Ts = 1.0 / Fs
-
-frequencies = (1 + np.arange(Nfreq)) * 1e3
+Fsym = 1 / Tsym
+frequencies = F0 + np.arange(Nfreq) * Fsym
 carrier_index = 0
 Fc = frequencies[carrier_index]
 Tc = 1.0 / Fc
diff --git a/scripts/amodem b/scripts/amodem
index 4ebdc7c..f16ffa2 100755
--- a/scripts/amodem
+++ b/scripts/amodem
@@ -11,6 +11,9 @@ import logging
 format = '%(asctime)s %(levelname)-10s %(message)-100s %(filename)s:%(lineno)d'
 logging.basicConfig(level=logging.DEBUG, format=format)
 
+log = logging.getLogger('__name__')
+
+from amodem import config
 from amodem import recv
 from amodem import send
 from amodem import wave
@@ -97,6 +100,8 @@ def main():
     if getattr(args, 'plt', 'None'):
         import pylab
         args.plt = pylab
+
+    log.debug('MODEM settings: %r', config.settings)
     args.main(args)
 
 def run(args, process):