UmTRX: Manually set Tx gain stages for the best signal quality.

New UHD versions support split configuration of Tx gain stages.
We utilize this to set the gain configuration, optimal for
the Tx signal quality. From our measurements, VGA1 must be
18dB plus-minus one and VGA2 is the best when 23dB or lower.

1 files changed, 39 insertions, 5 deletions

diff --git a/Transceiver52M/UHDDevice.cpp b/Transceiver52M/UHDDevice.cpp
index bdeb1b5..48b89d6 100644
--- a/Transceiver52M/UHDDevice.cpp
+++ b/Transceiver52M/UHDDevice.cpp
@@ -40,6 +40,8 @@
 #define TX_AMPL          0.3
 #define SAMPLE_BUF_SZ    (1 << 20)
 
+#define UMTRX_VGA1_DEF   -18
+
 enum uhd_dev_type {
 	USRP1,
 	USRP2,
@@ -421,9 +423,23 @@ void uhd_device::init_gains()
 {
 	uhd::gain_range_t range;
 
-	range = usrp_dev->get_tx_gain_range();
-	tx_gain_min = range.start();
-	tx_gain_max = range.stop();
+	if (dev_type == UMTRX) {
+		std::vector<std::string> gain_stages = usrp_dev->get_tx_gain_names(0);
+		if (gain_stages[0] == "VGA") {
+			LOG(WARNING) << "Update your UHD version for a proper Tx gain support";
+			range = usrp_dev->get_tx_gain_range();
+			tx_gain_min = range.start();
+			tx_gain_max = range.stop();
+		} else {
+			range = usrp_dev->get_tx_gain_range("VGA2");
+			tx_gain_min = UMTRX_VGA1_DEF + range.start();
+			tx_gain_max = UMTRX_VGA1_DEF + range.stop();
+		}
+	} else {
+		range = usrp_dev->get_tx_gain_range();
+		tx_gain_min = range.start();
+		tx_gain_max = range.stop();
+	}
 
 	range = usrp_dev->get_rx_gain_range();
 	rx_gain_min = range.start();
@@ -514,8 +530,26 @@ double uhd_device::setTxGain(double db, size_t chan)
 		return 0.0f;
 	}
 
-	usrp_dev->set_tx_gain(db, chan);
-	tx_gains[chan] = usrp_dev->get_tx_gain(chan);
+	if (dev_type == UMTRX) {
+		std::vector<std::string> gain_stages = usrp_dev->get_tx_gain_names(0);
+		if (gain_stages[0] == "VGA") {
+			LOG(WARNING) << "Update your UHD version for a proper Tx gain support";
+			usrp_dev->set_tx_gain(db, chan);
+			tx_gains[chan] = usrp_dev->get_tx_gain(chan);
+		} else {
+			// New UHD versions support split configuration of
+			// Tx gain stages. We utilize this to set the gain
+			// configuration, optimal for the Tx signal quality.
+			// From our measurements, VGA1 must be 18dB plus-minus
+			// one and VGA2 is the best when 23dB or lower.
+			usrp_dev->set_tx_gain(UMTRX_VGA1_DEF, "VGA1", chan);
+			usrp_dev->set_tx_gain(db-UMTRX_VGA1_DEF, "VGA2", chan);
+			tx_gains[chan] = usrp_dev->get_tx_gain(chan);
+		}
+	} else {
+		usrp_dev->set_tx_gain(db, chan);
+		tx_gains[chan] = usrp_dev->get_tx_gain(chan);
+	}
 
 	LOG(INFO) << "Set TX gain to " << tx_gains[chan] << "dB";