From 0cecaf72e5a7b1ee2ecc81fd11d72b7cf27e7d72 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jan=20K=C3=A4berich?= <j.kaeberich@gmx.de>
Date: Mon, 6 Jun 2022 17:28:03 +0200
Subject: [PATCH] Prevent higher frequency output spike when sweep starts at DC

---
 .../.settings/stm32cubeide.project.prefs             |  4 ++--
 Software/VNA_embedded/Application/VNA.cpp            | 12 +++++++++---
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/Software/VNA_embedded/.settings/stm32cubeide.project.prefs b/Software/VNA_embedded/.settings/stm32cubeide.project.prefs
index 586dde5..60e3eec 100644
--- a/Software/VNA_embedded/.settings/stm32cubeide.project.prefs
+++ b/Software/VNA_embedded/.settings/stm32cubeide.project.prefs
@@ -1,5 +1,5 @@
-2F62501ED4689FB349E356AB974DBE57=EF826FD321FB312AEADE4DB74B81458C
+2F62501ED4689FB349E356AB974DBE57=6F84FD31C089E822CF61FFCABCD0B7D1
 66BE74F758C12D739921AEA421D593D3=2
-8DF89ED150041C4CBC7CB9A9CAA90856=EF826FD321FB312AEADE4DB74B81458C
+8DF89ED150041C4CBC7CB9A9CAA90856=6F84FD31C089E822CF61FFCABCD0B7D1
 DC22A860405A8BF2F2C095E5B6529F12=6E2D4146EA2709ED1E4A1764BC291F57
 eclipse.preferences.version=1
diff --git a/Software/VNA_embedded/Application/VNA.cpp b/Software/VNA_embedded/Application/VNA.cpp
index 4e3e4e5..52cf778 100644
--- a/Software/VNA_embedded/Application/VNA.cpp
+++ b/Software/VNA_embedded/Application/VNA.cpp
@@ -404,12 +404,18 @@ void VNA::SweepHalted() {
 		}
 
 		// need the Si5351 as Source
-		Si5351.SetCLK(SiChannel::LowbandSource, frequency, Si5351C::PLL::B, driveStrength);
+		bool freqSuccess = Si5351.SetCLK(SiChannel::LowbandSource, frequency, Si5351C::PLL::B, driveStrength);
+		static bool lowbandDisabled = false;
 		if (pointCnt == 0) {
-			// First point in sweep, enable CLK
-			Si5351.Enable(SiChannel::LowbandSource);
+			// First point in sweep, switch to correct source
 			FPGA::Disable(FPGA::Periphery::SourceRF);
+			lowbandDisabled = true;
+		}
+		if(lowbandDisabled && freqSuccess) {
+			// frequency is valid, can enable lowband source now
+			Si5351.Enable(SiChannel::LowbandSource);
 			Delay::us(1300);
+			lowbandDisabled = false;
 		}
 
 		// At low frequencies the 1.LO feedthrough mixes with the 2.LO in the second mixer.