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diff --git a/octave/fsk_lib_ldpc.m b/octave/fsk_lib_ldpc.m
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+% fsk_lib_ldpc.m
+%
+% Library of common functions used for LDPC coded 4FSK modem experiments
+
+fsk_lib;
+ldpc;
+
+% set up modem waveform, real signal that an pass through a SSB radio
+function [states M] = modem_init(Rs,Fs,df)
+  M  = 4;
+  if Rs == 100 P=8; end
+  if Rs == 400 P=10; end;
+  states = fsk_init(Fs,Rs,M,P=10,nsym=100);
+  states.tx_real = 1;
+  states.tx_tone_separation = Rs;
+  if Rs == 100
+    states.ftx = 1500 -2.5*states.tx_tone_separation + states.tx_tone_separation*(1:M);
+  elseif Rs == 400
+    states.ftx = 600 + states.tx_tone_separation*(0:M-1);
+  else
+    disp("unknown symbol rate");
+  end  
+  states.fest_fmin = 500;
+  states.fest_fmax = 2500;
+  states.fest_min_spacing = Rs/2;
+  states.df = df;
+
+  states.ber_valid_thresh = 0.1;
+  states.ber_invalid_thresh = 0.2;
+
+  states.amp_scale = 1000;
+end
+
+% set up modem waveform and LPC code
+function [states code_param] = fsk_lib_ldpc_init (HRA, Rs, Fs, df=0, plots=0)
+  [states M] = modem_init(Rs, Fs, df);
+  N = states.N;
+  if plots; states.verbose = 0x4; end
+
+  Hsize=size(HRA); 
+  states.rate = (Hsize(2)-Hsize(1))/Hsize(2);
+  code_param = ldpc_init_user(HRA, modulation='FSK', mod_order=states.M, mapping='gray');
+  states.coden = code_param.coded_bits_per_frame;
+  states.codek = code_param.data_bits_per_frame;
+end