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diff --git a/octave/ofdm_tx.m b/octave/ofdm_tx.m
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+% ofdm_tx.m
+% David Rowe March 2018
+%
+% File based, uncoded OFDM tx.  Generates a file of ofdm samples,
+% including optional channel simulation.  See also ofdm_ldpc_tx.m, and
+% ofdm_mod.c
+
+#{
+  Examples:
+
+  i) 10 seconds, AWGN channel at SNR3k=3dB
+
+    octave:4> ofdm_tx("awgn_snr_3dB_700d.raw", "700D", 10, 3)
+
+  ii) 10 seconds, multipath poor channel at SNR=6dB
+
+    octave:5> ofdm_tx("hf_snr_6dB_700d.raw", "700D", 10, 6, "mpp")
+    
+  iii) Data mode example, three bursts of one packet each, SNR=100dB:
+  
+    octave:6> ofdm_tx("test_datac0.raw","datac0",1,100,"awgn","bursts",3)
+
+#}
+
+function ofdm_tx(filename, mode="700D", N, SNR3kdB=100, channel='awgn', varargin)
+  ofdm_lib;
+  channel_lib;
+  randn('seed',1);
+  pkg load signal;
+
+  tx_clip_en = 0; freq_offset_Hz = 0.0; burst_mode = 0; Nbursts = 1;
+  i = 1;
+  while i<=length(varargin)
+    if strcmp(varargin{i},"txclip") 
+      tx_clip_en = 1;
+    elseif strcmp(varargin{i},"bursts") 
+      burst_mode = 1;
+      Nbursts = varargin{i+1}; i++;
+    else
+      printf("\nERROR unknown argument: [%d] %s \n", i ,varargin{i});
+      return;
+    end
+    i++;
+  end
+  
+  % init modem
+
+  config = ofdm_init_mode(mode);
+  states = ofdm_init(config);  
+  print_config(states);
+  ofdm_load_const;
+
+  if burst_mode
+    % burst mode: treat N as Npackets
+    Npackets = N; 
+ else
+    % streaming mode: treat N as Nseconds
+    Npackets = round(N/states.Tpacket);
+  end
+
+  % Generate fixed test frame of tx bits and concatenate packets
+
+  tx_bits = create_ldpc_test_frame(states, coded_frame=0);
+  atx = ofdm_mod(states, tx_bits);
+  tx = [];
+  for f=1:Npackets
+    tx = [tx atx];
+  end
+  if length(states.data_mode)
+    % note postamble provides a "column" of pilots at the end of the burst
+    tx = [states.tx_preamble tx states.tx_postamble];
+  end
+  
+  % if burst mode concatenate multiple bursts with spaces
+  if burst_mode
+    atx = tx; tx = zeros(1,states.Fs); on_time = 0; off_time = states.Fs;
+    for b=1:Nbursts
+      tx = [tx atx zeros(1,states.Fs)];
+      on_time += length(atx);
+      off_time += states.Fs;
+    end
+    % adjust channel simulator SNR setpoint given (burst on length)/(total length including silence) ratio
+    mark_space_SNR_offset = 10*log10(on_time/(on_time+off_time));
+    SNRdB_setpoint = SNR3kdB + mark_space_SNR_offset;
+    printf("SNR3kdB: %4.2f Burst offset: %4.2f SNRdB_setpoint: %4.2f\n", SNR3kdB, mark_space_SNR_offset, SNRdB_setpoint)
+  else
+    SNRdB_setpoint = SNR3kdB; % no adjustment to SNR in streaming mode
+  end
+  
+  printf("Npackets: %d  Nbursts: %d  ", Npackets, Nbursts);
+  states.verbose=1;
+  tx = ofdm_hilbert_clipper(states, tx, tx_clip_en);
+  rx_real = ofdm_channel(states, tx, SNRdB_setpoint, channel, freq_offset_Hz);
+  frx = fopen(filename,"wb"); fwrite(frx, rx_real, "short"); fclose(frx);
+endfunction