From 7495ea66d2efa2c9f42224cea01c5f2f45a9f555 Mon Sep 17 00:00:00 2001
From: c vw <dl1ycf@darc.de>
Date: Thu, 5 Nov 2020 14:46:38 +0100
Subject: [PATCH] Better "drive level adjustment" for HermesLite2

---
 old_protocol.c | 16 ++++++++++++++++
 transmitter.c  | 30 ++++++++++++++++++++++++++++++
 2 files changed, 46 insertions(+)

diff --git a/old_protocol.c b/old_protocol.c
index c66d500..4c9345d 100644
--- a/old_protocol.c
+++ b/old_protocol.c
@@ -1683,6 +1683,22 @@ static int last_power=0;
           } else {
             power=transmitter->drive_level;
           }
+          if (device == DEVICE_HERMES_LITE2) {
+            //
+            // from the "intended" drive level power, calculate the
+            // next lower TX attenuation which can be from 0.0 to -7.5 dB
+            // in 0.5 dB steps, encode the step in a four-bit word and shift
+            // it to the upper 4 bits.
+            // we always use the att level that produces a little bit *less* attenuation
+            // than required, and down-scale the IQ samples in transmitter.c
+            //
+            if (power > 0) {
+              int hl2power = 15+(int)lround(ceil(40.0 * log10((double) power / 255.0)));
+              if (hl2power < 0) hl2power=0;
+	      // hl2power=0: -7.5 dB, hl2power=1: -7.0 dB, ..., hl2power=15: 0dB
+              power=hl2power << 4;  // shift to upper bits
+            }
+          }
         }
 
 //if(last_power!=power) {
diff --git a/transmitter.c b/transmitter.c
index 9cba43c..6054862 100644
--- a/transmitter.c
+++ b/transmitter.c
@@ -1089,6 +1089,36 @@ static void full_tx_buffer(TRANSMITTER *tx) {
         gain=gain*(double)transmitter->drive_level*0.00392;
       }
     }
+    if (protocol == ORIGINAL_PROTOCOL && radio->device == DEVICE_HERMES_LITE2) {
+      //
+      // The HermesLite2 is built around the AD9866 modem chip. The TX level can
+      // be adjusted from 0.0 to -7.5 dB in 0.5 db steps, and these settings are
+      // encoded in the top 4 bits of the HPSDR "drive level".
+      //
+      // In old_protocol.c, the TX attenuator is set according to the drive level,
+      // here we only apply a (mostly small) additional damping of the IQ samples
+      // to achieve a smooth drive level adjustment.
+      // However, if the drive level requires an attenuation *much* larger than
+      // 7.5 dB we have to damp significantly at this place, which may affect IMD.
+      //
+      int power;
+      double f,g;
+      if(tune && !transmitter->tune_use_drive) {
+        f=sqrt((double)transmitter->tune_percent * 0.01);
+        power=(int)((double)transmitter->drive_level*f);
+      } else {
+        power=transmitter->drive_level;
+      }
+      g=-15.0;
+      if (power > 0) {
+        f = 40.0 * log10((double) power / 255.0);   // 2* attenuation in dB
+        g= ceil(f);                                 // 2* attenuation rounded to half-dB steps
+        if (g < -15.0) g=-15.0;                     // nominal TX attenuation
+        gain=gain*pow(10.0,0.05*(f-g));
+      } else {
+        gain=0.0;
+      }
+    }
 
     if (txflag == 0 && protocol == NEW_PROTOCOL) {
 	//
-- 
2.45.2