function setModelType(f,option_no) {
  var i=0;
  
  // clear selection options	 
  while (i < f.category.length) {
    f.category.options[i] = null;
    i++;
  }

    f.category.options[0] = new Option("Choose Mixer Type","fm_coax_rugged.html");

  if (option_no == "coax") {
    f.category.length = 8;
    f.category.options[1] = new Option("Level 3,4","fm_coax_rugged.html");
    f.category.options[2] = new Option("Level 7","fm_coax_level_7.html");
    f.category.options[3] = new Option("Level 10","fm_coax_level_10.html");
    f.category.options[4] = new Option("Level 13","fm_coax_level_13.html");
    f.category.options[5] = new Option("Level 17","fm_coax_level_17.html");
    f.category.options[6] = new Option("Level 23","fm_coax_level_23.html");
    f.category.options[7] = new Option("Up Converter","fm_coax_up.html");
  }
  else if (option_no == "pi") {
    f.category.length = 8;
    f.category.options[1] = new Option("Active","fm_pic_active.html");
    f.category.options[2] = new Option("Level 7","fm_pic_level_7.html");
    f.category.options[3] = new Option("Level 10","fm_pic_level_10.html");
    f.category.options[4] = new Option("Level 13","fm_pic_level_13.html");
    f.category.options[5] = new Option("Level 17","fm_pic_level_17.html");
    f.category.options[6] = new Option("Level 23","fm_pic_level_23.html");
    f.category.options[7] = new Option("Level 27","fm_pic_level_27.html");
  }
  else if (option_no == "sm") {
    f.category.length =11;
    f.category.options[1] = new Option("Active, High IP3","fm_sm_active.html");
    f.category.options[2] = new Option("High IP3 (up to 37 dBm)","fm_sm_hi_ip3_1.html");
    f.category.options[3] = new Option("High Reliability","fm_sm_level_hr.html");
    f.category.options[4] = new Option("Image Reject","fm_sm_image_reject.html");
    f.category.options[5] = new Option("Level 3-4","fm_sm_level_3.html");
    f.category.options[6] = new Option("Level 7","fm_sm_level_7.html");
    f.category.options[7] = new Option("Level 10","fm_sm_level_10.html");
    f.category.options[8] = new Option("Level 13","fm_sm_level_13.html");
    f.category.options[9] = new Option("Level 17","fm_sm_level_17.html");
    f.category.options[10] = new Option("Up Converter","fm_sm_up.html");
  }
  else if(option_no == "lt") {
    f.category.length = 7;
    f.category.options[1] = new Option("Level 3-4", "fm_sm_level_3_ltcc.html");
    f.category.options[2] = new Option("Level 7","fm_sm_level_7_ltcc.html");
    f.category.options[3] = new Option("Level 10","fm_sm_level_10_ltcc.html");
    f.category.options[4] = new Option("Level 13","fm_sm_level_13_ltcc.html");
    f.category.options[5] = new Option("Level 17","fm_sm_level_17_ltcc.html");
    f.category.options[6] = new Option("Up Converters","fm_sm_up_ltcc.html");
  }
}