diff --git a/TNC/AFSKModulator.cpp b/TNC/AFSKModulator.cpp
index e169216..d4d1c66 100644
--- a/TNC/AFSKModulator.cpp
+++ b/TNC/AFSKModulator.cpp
@@ -9,11 +9,7 @@ void AFSKModulator::init(const kiss::Hardware& hw)
 {
     set_twist(hw.tx_twist);
 
-    if (HAL_RCC_GetHCLKFreq() != 48000000)
-    {
-        ERROR("Clock is not 48MHz");
-        CxxErrorHandler();
-    }
+    SysClock48();
 
     // Configure 48MHz clock for 26.4ksps.
     htim7.Init.Period = 1817;
diff --git a/TNC/Fsk9600Demodulator.hpp b/TNC/Fsk9600Demodulator.hpp
index 5abe2dd..a4ce20d 100644
--- a/TNC/Fsk9600Demodulator.hpp
+++ b/TNC/Fsk9600Demodulator.hpp
@@ -51,7 +51,6 @@ struct Fsk9600Demodulator : IDemodulator
 
     void start() override
     {
-        INFO("Setting 80MHz SysClock.");
         SysClock80();
 
         auto const& bpf_coeffs = bpf_bank[kiss::settings().rx_twist + 3];
diff --git a/TNC/Fsk9600Modulator.cpp b/TNC/Fsk9600Modulator.cpp
index e04f2c0..2f2d7b7 100644
--- a/TNC/Fsk9600Modulator.cpp
+++ b/TNC/Fsk9600Modulator.cpp
@@ -6,16 +6,26 @@
 namespace mobilinkd { namespace tnc {
 
 /*
+ * Cosine.
 const Fsk9600Modulator::cos_table_type Fsk9600Modulator::cos_table = {
     2047,  2020,  1937,  1801,  1616,  1387,  1120,   822,   502,   169,
     -169,  -502,  -822, -1120, -1387, -1616, -1801, -1937, -2020, -2048
 };
 */
 
+/*
+ * Square wave -- filtered in hardware at 7200Hz
 const Fsk9600Modulator::cos_table_type Fsk9600Modulator::cos_table = {
      2047,  2047,  2047,  2047,  2047,  2047,  2047,  2047,  2047,  2047,
     -2048, -2048, -2048, -2048, -2048, -2048, -2048, -2048, -2048, -2048
 };
+*/
+
+// Gaussian
+const Fsk9600Modulator::cos_table_type Fsk9600Modulator::cos_table = {
+    2042,  2027,  1995,  1931,  1815,  1626,  1345,   968,   507,     0,
+    -507,  -968, -1345, -1626, -1815, -1931, -1995, -2027, -2042, -2048
+};
 
 void Fsk9600Modulator::init(const kiss::Hardware& hw)
 {
@@ -26,11 +36,7 @@ void Fsk9600Modulator::init(const kiss::Hardware& hw)
     state = State::STOPPED;
     level = Level::HIGH;
 
-    if (HAL_RCC_GetHCLKFreq() != 80000000)
-    {
-        ERROR("Clock is not 80MHz");
-        CxxErrorHandler();
-    }
+    SysClock80();
 
     // Configure 80MHz clock for 192ksps.
     htim7.Init.Period = 416;
diff --git a/TNC/Fsk9600Modulator.hpp b/TNC/Fsk9600Modulator.hpp
index aceeaf9..5bc53d2 100644
--- a/TNC/Fsk9600Modulator.hpp
+++ b/TNC/Fsk9600Modulator.hpp
@@ -211,8 +211,8 @@ private:
         case Level::LOW:
             if (bit)
             {
-                std::transform(cos_table.rbegin(), cos_table.rend(), buffer,
-                    [this](auto x){return adjust_level(x);});
+                std::transform(cos_table.begin(), cos_table.end(), buffer,
+                    [this](auto x){return adjust_level(-1 - x);});
                 level = Level::HIGH;
             }
             else