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 Amplifier Type:","amplifiers_ip3.html");

  if (option_no == "coax") {
    f.category.options[1] = new Option("High Power","amplifiers_power.html");
    f.category.options[2] = new Option("Low Noise","amplifiers_low_noise.html");
    f.category.options[3] = new Option("Pulse Amplifiers","amplifiers_pulse.html");
    f.category.options[4] = new Option("RF Instrument","amplifiers_rf.html");
    f.category.options[5] = new Option("Variable Gain","amplifiers_variable.html");
    f.category.options[6] = new Option("Wideband","amplifiers_wideband.html");
  }
  else if (option_no == "pi") {
    f.category.options[1] = new Option("Power","amplifiers_pic_power.html");
    location.href="amplifiers_pic_power.html";
  }
  else if (option_no == "sm") {
    f.category.options[1] = new Option("Show All","amplifiers_sm_all.html");
    f.category.options[2] = new Option("E-PHEMT,Ultra Low Noise","amplifiers_ephemt_low_noise.html");
    f.category.options[3] = new Option("Dual Matched Monolithic","amplifiers_dual_monolithic.html");
    f.category.options[4] = new Option("High IP3","amplifiers_ip3.html");
    f.category.options[5] = new Option("Show All Gain Blocks","amplifiers_show_all_gain.html");
    f.category.options[6] = new Option("Low Noise Amplifiers/Modules","amplifiers_low_noise_sm.html");
    f.category.options[7] = new Option("Monolithic Gain Block","amplifiers_monolithic.html")   
  }

}