Fix Elecraft K4 set_mode to work with VFOB

https://github.com/Hamlib/Hamlib/issues/825

rigs/kenwood/k3.c

@@ -484,7 +484,7 @@ const struct rig_caps k4_caps =
     RIG_MODEL(RIG_MODEL_K4),
     .model_name =       "K4",
     .mfg_name =     "Elecraft",
-    .version =      BACKEND_VER ".14",
+    .version =      BACKEND_VER ".15",
     .copyright =        "LGPL",
     .status =       RIG_STATUS_STABLE,
     .rig_type =     RIG_TYPE_TRANSCEIVER,
@@ -1088,9 +1088,11 @@ int k3_get_mode(RIG *rig, vfo_t vfo, rmode_t *mode, pbwidth_t *width)
 int k3_set_mode(RIG *rig, vfo_t vfo, rmode_t mode, pbwidth_t width)
 {
     int err;
-    char cmd_m[4];
+    char cmd_m[5];
     char buf[KENWOOD_MAX_BUF_LEN];
+    char *dtcmd;
     struct kenwood_priv_caps *caps = kenwood_caps(rig);
+    struct kenwood_priv_data *priv = rig->state.priv;
 
     rig_debug(RIG_DEBUG_VERBOSE, "%s called\n", __func__);
 
@@ -1112,40 +1114,46 @@ int k3_set_mode(RIG *rig, vfo_t vfo, rmode_t mode, pbwidth_t width)
     else
     {
         rig_debug(RIG_DEBUG_TRACE,
-                  "%s(%d): changing mode=%s, oldmode=%s, width=%ld, oldwidth=%ld\n", __FILE__,
+                  "%s(%d): changing oldmode=%s, to mode=%s, oldwidth=%ld, to width=%ld\n", __FILE__,
                   __LINE__, rig_strrmode(tmode), rig_strrmode(mode), twidth, width);
     }
 
+    dtcmd = "DT";
+    if ((priv->is_k4 || priv->is_k4d || priv->is_k4hd)  && vfo == RIG_VFO_B)
+    {
+        dtcmd = "DT$";
+    }
+
     switch (mode)
     {
     case RIG_MODE_PKTLSB:
         mode = RIG_MODE_RTTYR; // in "DT0" Subband RIG_MODE_RTTYR = USB and RIG_MODE_RTTY = LSB
         snprintf(cmd_m, sizeof(cmd_m),
-                 "DT0"); /* DATA A mode - DATA (REV) on LSB optimized for HF Packet, VFO dial is suppressed carrier QRG */
+                 "%s0", dtcmd); /* DATA A mode - DATA (REV) on LSB optimized for HF Packet, VFO dial is suppressed carrier QRG */
         break;
 
     case RIG_MODE_PKTUSB:
         mode = RIG_MODE_RTTY; // in "DT0" Subband RIG_MODE_RTTYR = USB and RIG_MODE_RTTY = LSB
         snprintf(cmd_m, sizeof(cmd_m),
-                 "DT0"); /* DATA A mode - DATA on USB general, VFO dial is suppressed carrier QRG */
+                 "%s0", dtcmd); /* DATA A mode - DATA on USB general, VFO dial is suppressed carrier QRG */
         break;
 
     case RIG_MODE_RTTY:
         mode = RIG_MODE_RTTY; // in "DT1" Subband RIG_MODE_RTTY = LSB and RIG_MODE_RTTYR = USB
         snprintf(cmd_m, sizeof(cmd_m),
-                 "DT2"); /* FSK D mode - direct FSK on LSB optimized for RTTY, VFO dial is MARK */
+                 "%s2", dtcmd); /* FSK D mode - direct FSK on LSB optimized for RTTY, VFO dial is MARK */
         break;
 
     case RIG_MODE_RTTYR:
         mode = RIG_MODE_RTTYR; // in "DT2" Subband RIG_MODE_RTTY = LSB and RIG_MODE_RTTYR = USB
         snprintf(cmd_m, sizeof(cmd_m),
-                 "DT1"); /* FSK D mode - direct FSK keying, LSB is "normal", VFO dial is MARK */
+                 "%s1", dtcmd); /* FSK D mode - direct FSK keying, LSB is "normal", VFO dial is MARK */
         break;
 
     case RIG_MODE_PSK:
         mode = RIG_MODE_PSK; // in "DT3" subband RIG_MODE_PSK = USB # kenwood.c mode but may need kenwwod.c mode table review.
         snprintf(cmd_m, sizeof(cmd_m),
-                 "DT3"); /* PSK D Mode - direct PSK keying, USB is "normal", VFO dial is MARK */
+                 "%s3", dtcmd); /* PSK D Mode - direct PSK keying, USB is "normal", VFO dial is MARK */
         break;
 
     default: