diff --git a/README.md b/README.md
index 578a0e0..2fffcb2 100644
--- a/README.md
+++ b/README.md
@@ -93,6 +93,9 @@ PTRS
 SSB
 : Single Sideband (half of an AM signal with the central carrier suppressed. Commonly Upper Sideband, except Ham voice below 10 MHz.)
 
+SWL
+: Short Wave (Radio) Listening
+
 UHF
 : Ultra High Frequency 300 - 3000 MHz