From 1c2e9180a2db989f26c5cff01eaa6ef12bb45011 Mon Sep 17 00:00:00 2001
From: Andreas Eversberg <jolly@eversberg.eu>
Date: Sat, 19 Aug 2017 12:21:35 +0200
Subject: [PATCH] Radiocom 2000: Use high-pass filter to remove supervisory
 signal

---
 src/r2000/dsp.c   | 11 ++++++++++-
 src/r2000/r2000.h |  2 ++
 2 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/src/r2000/dsp.c b/src/r2000/dsp.c
index 3b9dbd2..73a6d95 100644
--- a/src/r2000/dsp.c
+++ b/src/r2000/dsp.c
@@ -60,7 +60,7 @@
 #define SUPER_BIT_ADJUST	0.5	/* how much do we adjust bit clock on frequency change */
 #define SUPER_F0		136.0
 #define SUPER_F1		164.0
-#define FILTER_STEP		0.002	/* step every 2 ms */
+#define SUPER_CUTOFF_H		400.0	/* filter to remove spectrum of supervisory signal */
 #define MAX_DISPLAY		1.4	/* something above dBm0 */
 
 /* global init for FSK */
@@ -102,6 +102,13 @@ int dsp_init_sender(r2000_t *r2000)
 		return -EINVAL;
 	}
 
+	/* remove frequencies of supervisory spectrum:
+	 * TX = remove low frequencies from speech to be transmitted
+	 * RX = remove received supervisory signal
+	 */
+	iir_highpass_init(&r2000->super_tx_hp, SUPER_CUTOFF_H, r2000->sender.samplerate, 2);
+	iir_highpass_init(&r2000->super_rx_hp, SUPER_CUTOFF_H, r2000->sender.samplerate, 2);
+
 	return 0;
 }
 
@@ -248,6 +255,7 @@ void sender_receive(sender_t *sender, sample_t *samples, int length)
 	 && r2000->callref) {
 		int count;
 
+		iir_process(&r2000->super_rx_hp, samples, length);
 		count = samplerate_downsample(&r2000->sender.srstate, samples, length);
 #if 0
 		/* compandor only in direction REL->MS */
@@ -314,6 +322,7 @@ again:
 	case DSP_MODE_AUDIO_TX:
 	case DSP_MODE_AUDIO_TX_RX:
 		jitter_load(&r2000->sender.dejitter, samples, length);
+		iir_process(&r2000->super_tx_hp, samples, length);
 		/* do pre-emphasis */
 		if (r2000->pre_emphasis)
 			pre_emphasis(&r2000->estate, samples, length);
diff --git a/src/r2000/r2000.h b/src/r2000/r2000.h
index 6eb0bc5..6d5ad46 100644
--- a/src/r2000/r2000.h
+++ b/src/r2000/r2000.h
@@ -99,10 +99,12 @@ typedef struct r2000 {
 	uint32_t		super_tx_word;		/* supervisory info to transmit */
 	int			super_tx_word_length;
 	int			super_tx_word_pos;
+	iir_filter_t		super_tx_hp;		/* filters away the speech that overlaps with the supervisory */
 	uint32_t		super_rx_word;		/* shift register for received supervisory info */
 	double			super_rx_level[20];	/* level infos */
 	double			super_rx_quality[20];	/* quality infos */
 	int			super_rx_index;		/* index for level and quality buffer */
+	iir_filter_t		super_rx_hp;		/* filters away the supervisory */
 double super_bittime;
 double super_bitpos;