diff --git a/srslte/examples/usrp_txrx.c b/srslte/examples/usrp_txrx.c
index 298aa30ee..33c21be9f 100644
--- a/srslte/examples/usrp_txrx.c
+++ b/srslte/examples/usrp_txrx.c
@@ -40,23 +40,26 @@
 uint32_t nof_prb    = 25;
 uint32_t nof_frames = 20; 
 
+float tone_offset_hz = 0;
 float uhd_rx_gain=40, uhd_tx_gain=40, uhd_freq=2.4e9; 
 char *uhd_args="";
 char *output_filename = NULL;
 char *input_filename = NULL;
 
 void usage(char *prog) {
-  printf("Usage: %s -i [tx_signal_file] -o [rx_signal_file]\n", prog);
+  printf("Usage: %s -o [rx_signal_file]\n", prog);
   printf("\t-a UHD args [Default %s]\n", uhd_args);
   printf("\t-f UHD TX/RX frequency [Default %.2f MHz]\n", uhd_freq/1e6);
   printf("\t-g UHD RX gain [Default %.1f dB]\n", uhd_rx_gain);
   printf("\t-G UHD TX gain [Default %.1f dB]\n", uhd_tx_gain);
+  printf("\t-t Single tone offset (Hz) [Default %f]\n", tone_offset_hz);    
+  printf("\t-i File name to read signal from [Default single tone]\n");
   printf("\t-p Number of UL RB [Default %d]\n", nof_prb);  
 }
 
 void parse_args(int argc, char **argv) {
   int opt;
-  while ((opt = getopt(argc, argv, "ioafgp")) != -1) {
+  while ((opt = getopt(argc, argv, "ioafgpt")) != -1) {
     switch (opt) {
     case 'a':
       uhd_args = argv[optind];
@@ -67,6 +70,9 @@ void parse_args(int argc, char **argv) {
     case 'i':
       input_filename = argv[optind];
       break;
+    case 't':
+      tone_offset_hz = atof(argv[optind]);
+      break;
     case 'f':
       uhd_freq = atof(argv[optind]);
       break;
@@ -88,7 +94,7 @@ void parse_args(int argc, char **argv) {
       exit(-1);
     }
   }
-  if (!input_filename || !output_filename) {
+  if (!output_filename) {
     usage(argv[0]);
     exit(-1);
   }
@@ -127,17 +133,33 @@ int main(int argc, char **argv) {
     exit(-1);
   }
   cuhd_set_master_clock_rate(uhd, 30.72e6);        
+  
+  int srate = srslte_sampling_freq_hz(nof_prb);    
+  if (srate < 10e6) {          
+    cuhd_set_master_clock_rate(uhd, 4*srate);        
+  } else {
+    cuhd_set_master_clock_rate(uhd, srate);        
+  }
+  cuhd_set_rx_srate(uhd, (double) srate);
+  cuhd_set_tx_srate(uhd, (double) srate);
 
   printf("Subframe len:   %d samples\n", flen);
-  printf("Set TX/RX rate: %.2f MHz\n", cuhd_set_rx_srate(uhd, srslte_sampling_freq_hz(nof_prb)) / 1000000);
+  printf("Set TX/RX rate: %.2f MHz\n", (float) srate / 1000000);
   printf("Set RX gain: %.1f dB\n", cuhd_set_rx_gain(uhd, uhd_rx_gain));
   printf("Set TX gain: %.1f dB\n", cuhd_set_tx_gain(uhd, uhd_tx_gain));
   printf("Set TX/RX freq: %.2f MHz\n", cuhd_set_rx_freq(uhd, uhd_freq) / 1000000);
-  cuhd_set_tx_srate(uhd, srslte_sampling_freq_hz(nof_prb));
+  
   cuhd_set_tx_freq_offset(uhd, uhd_freq, 8e6);  
   sleep(1);
   
-  srslte_vec_load_file(input_filename, &tx_buffer[nsamples_adv], flen*sizeof(cf_t));
+  if (input_filename) {
+    srslte_vec_load_file(input_filename, &tx_buffer[nsamples_adv], flen*sizeof(cf_t));
+  } else {
+    for (int i=0;i<flen-nsamples_adv;i++) {
+      tx_buffer[i+nsamples_adv] = cexpf(_Complex_I*2*M_PI*tone_offset_hz*(float) i/(float) srate);       
+    }
+    srslte_vec_save_file("uhd_txrx_tone", tx_buffer, flen*sizeof(cf_t));
+  }
 
   srslte_timestamp_t tstamp; 
   
diff --git a/srslte/lib/sync/test/sync_test.c b/srslte/lib/sync/test/sync_test.c
index a0ff9d715..1e37c2c00 100644
--- a/srslte/lib/sync/test/sync_test.c
+++ b/srslte/lib/sync/test/sync_test.c
@@ -79,7 +79,7 @@ void parse_args(int argc, char **argv) {
 }
 
 int main(int argc, char **argv) {
-  int N_id_2, ns, find_ns;
+  int N_id_2, sf_idx, find_sf;
   cf_t *buffer, *fft_buffer;
   cf_t pss_signal[SRSLTE_PSS_LEN];
   float sss_signal0[SRSLTE_SSS_LEN]; // for subframe 0
@@ -104,7 +104,7 @@ int main(int argc, char **argv) {
     exit(-1);
   }
 
-  fft_buffer = malloc(sizeof(cf_t) * FLEN);
+  fft_buffer = malloc(sizeof(cf_t) * FLEN * 2);
   if (!fft_buffer) {
     perror("malloc");
     exit(-1);
@@ -142,28 +142,29 @@ int main(int argc, char **argv) {
 
     srslte_sync_set_N_id_2(&sync, N_id_2);
     
-    for (ns=0;ns<2;ns++) {
+    // SF1 is SF5 
+    for (sf_idx=0;sf_idx<2;sf_idx++) {
       memset(buffer, 0, sizeof(cf_t) * FLEN);
       srslte_pss_put_slot(pss_signal, buffer, nof_prb, cp);
-      srslte_sss_put_slot(ns?sss_signal5:sss_signal0, buffer, nof_prb, cp);
+      srslte_sss_put_slot(sf_idx?sss_signal5:sss_signal0, buffer, nof_prb, cp);
 
       /* Transform to OFDM symbols */
       memset(fft_buffer, 0, sizeof(cf_t) * FLEN);
-      srslte_ofdm_tx_slot(&ifft, buffer, &fft_buffer[offset]);
+      srslte_ofdm_tx_sf(&ifft, buffer, &fft_buffer[offset]);
       
       if (srslte_sync_find(&sync, fft_buffer, 0, &find_idx) < 0) {
         fprintf(stderr, "Error running srslte_sync_find\n");
         exit(-1);
       }
-      find_ns = 2*srslte_sync_get_sf_idx(&sync);
+      find_sf = srslte_sync_get_sf_idx(&sync);
       printf("cell_id: %d find: %d, offset: %d, ns=%d find_ns=%d\n", cid, find_idx, offset,
-          ns, find_ns);
+          sf_idx, find_sf);
       if (find_idx != offset + FLEN/2) {
         printf("offset != find_offset: %d != %d\n", find_idx, offset + FLEN/2);
         exit(-1);
       }
-      if (ns*10 != find_ns) {
-        printf("ns != find_ns\n", 10 * ns, find_ns);
+      if (sf_idx*5 != find_sf) {
+        printf("ns != find_ns\n");
         exit(-1);
       }
       if (srslte_sync_get_cp(&sync) != cp) {