diff --git a/GPS-Sim.md b/GPS-Sim.md
index ce72644..cc8b61b 100644
--- a/GPS-Sim.md
+++ b/GPS-Sim.md
@@ -4,7 +4,7 @@ This app allows you to broadcast GPS baseband signal data streams.
 You can use [gps-sdr-sim](https://github.com/osqzss/gps-sdr-sim) to generate data for this app.  
 
 `gps-sdr-sim -e brdc3540.14n -l LAT,LONG,HEIGHT -o BBD_NNNN.C8`
-That will create `BBD_NNNN.C8`
+That will create `BBD_NNNN.C8`, but note that you also need to specify its sample rate and frequency in another file, as explained below.
 
 ### Sample rate and frequency specification
 Create `BBD_NNNN.TXT` with: