From 1691a3dfb3c27e70155cb347a04affcc1879c8d5 Mon Sep 17 00:00:00 2001
From: f4exb <f4exb06@gmail.com>
Date: Fri, 5 Apr 2024 14:43:17 +0200
Subject: [PATCH] ChirpChat demod: optimize SFD detection

---
 plugins/channelrx/demodchirpchat/chirpchatdemodsink.cpp | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/plugins/channelrx/demodchirpchat/chirpchatdemodsink.cpp b/plugins/channelrx/demodchirpchat/chirpchatdemodsink.cpp
index 3fe3f8fd2..1c45b38ca 100644
--- a/plugins/channelrx/demodchirpchat/chirpchatdemodsink.cpp
+++ b/plugins/channelrx/demodchirpchat/chirpchatdemodsink.cpp
@@ -286,8 +286,10 @@ void ChirpChatDemodSink::processSample(const Complex& ci)
 
             m_preambleHistory[m_chirpCount] = imax;
             m_chirpCount++;
+            double preDrop = magsqPre - magsqSFD;
+            double dropRatio = -preDrop / magsqSFD;
 
-            if (magsqPre <  magsqSFD) // preamble drop
+            if ((preDrop <  0.0) && (dropRatio > 0.5)) // preamble drop
             {
                 m_magsqTotalAvg(magsqSFDTotal);