2 files changed, 8 insertions, 3 deletions
diff --git a/README.md b/README.md
index a8dd221..a1acc2d 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ usage: calctenna.py [-h] [-f [frequency]] [-V [velocity_factor]] [-q]
 optional arguments:
   -h, --help            show this help message and exit
   -f [frequency], --frequency [frequency]
-                        desired frequency in Hz
+                        desired frequency in Hz (e.g. 144800000 or 433e6, ...
   -V [velocity_factor], --velocity-factor [velocity_factor]
   -q, --quiet           print only result
 ```
diff --git a/calctenna.py b/calctenna.py
index c4670c1..79d6ce1 100755
--- a/calctenna.py
+++ b/calctenna.py
@@ -12,10 +12,11 @@ def run_argparse():
     argparser.add_argument(
         '-f',
         '--frequency',
+        required=True,
         metavar='frequency',
-        help='desired frequency in Hz',
+        help='desired frequency in Hz (e.g. 144800000 or 433e6, ...',
         nargs='?',
-        default='100e6'
+        #default='100e6'
     )
     argparser.add_argument(
         '-V',
@@ -32,6 +33,10 @@ def run_argparse():
     )
     args = argparser.parse_args()
 
+    if not args.frequency:
+        argparser.print_usage()
+        exit()
+
     return args
 
 def calc(args):