diff --git a/hardware/hackrf-one/README b/hardware/hackrf-one/README
index 54189a1c..a0112d35 100644
--- a/hardware/hackrf-one/README
+++ b/hardware/hackrf-one/README
@@ -41,6 +41,7 @@ PCB description: 4 layer PCB 0.062 in
     Copper        4   0.5 oz foil plated to approximately 0.0017 in
 
 FR4 or similar substrate with Er=4.5 (+/- 0.1)
+required impedance: 50 ohm (+/- 5%) 20 mil microstrip impedance
 double side solder mask green
 single side silkscreen white
 6 mil min trace width and