--- a/test-fsk/modem_rx.c	Mon Mar 04 23:21:07 2024 -0800
+++ b/test-fsk/modem_rx.c	Tue Mar 05 10:57:45 2024 -0800
@@ -14,7 +14,58 @@
 
 extern int fsk_mode_rx;
 
+#define	MAX_TEXT_LINE	80
+
 static fsk_rx_state_t *fsk_rx_state;
+static u_char rx_line_buf[MAX_TEXT_LINE];
+static unsigned rx_buf_fill;
+
+static void
+safe_print_char(c)
+{
+	if (c >= ' ' && c <= '~') {
+		putchar(c);
+		return;
+	}
+	switch (c) {
+	case '\t':
+		putchar(c);
+		return;
+	case '\n':
+		return;
+	case '\r':
+		putchar('\\');
+		putchar('r');
+		return;
+	case '\b':
+		putchar('\\');
+		putchar('b');
+		return;
+	case '\f':
+		putchar('\\');
+		putchar('f');
+		return;
+	}
+	printf("\\x%02X", c);
+}
+
+static void
+print_rx_line()
+{
+	u_char *dp, *endp;
+	int c;
+
+	fputs("MRx:\t", stdout);
+	dp = rx_line_buf;
+	endp = rx_line_buf + rx_buf_fill;
+	while (dp < endp) {
+		c = *dp++;
+		safe_print_char(c);
+	}
+	if (c != '\n')
+		putchar('\\');
+	putchar('\n');
+}
 
 static void
 byte_rx_func(user_data, byte)
@@ -25,7 +76,11 @@
 		printf("Modem state change: %s\n", signal_status_to_str(byte));
 		return;
 	}
-	printf("Rx byte: 0x%02X\n", byte);
+	rx_line_buf[rx_buf_fill++] = byte;
+	if (byte == '\n' || rx_buf_fill >= MAX_TEXT_LINE) {
+		print_rx_line();
+		rx_buf_fill = 0;
+	}
 }
 
 void