OptLowpass™ is a specialized program written to expedite the design of transmitter output lowpass filters, especially for the HF amateur radio bands.

Here are some pertinent features:

• OptLowpass is 32-bit Windows® electrical filter design program written specifically to help the radio amateur design transmitter output harmonic-suppressing lowpass filters.
  
  
• It is based on the author's article "Harmonic Filters, Improved" which was in the September/October 1998 issue of QEX, an ARRL publication.
  
  
• On startup, the program presents pre-designed lowpass filters for each of the HF amateur bands, using ideal parts values as outlined in the above-mentioned article. You may also recall the last design session, recall a previously-saved design or invoke the Design Wizard.
  
  
• The design page shows the schematic of the filter as designed and a plot of the responses of that filter (both transmission and reflection).
  
  
• The capacitors' ideal values can then be adjusted by entering values in textboxes or they can be "tuned" upward or downward in 1% steps with the results immediately replotted right on the same screen.
  
  
• The inductors are assumed to be toroidal and, given a user-chosen value of core material AL, are specified in turns instead of the usual textbook "ideal" values.
  
  
• With an option switch, the toroidal inductance values can be adjusted by inductance value (textbox entry or by percent steps, like the capacitors) instead of by number of turns.
  
  
• The response using the current component values can be saved and later retrieved and overlaid on the current-value plots.
  
  
• A design as edited can be saved using a user-specified name and path for recall later.
  
  
• All of the various data files are in ordinary text format for ease of editing or examination outside the program.
  
  
• Pressing the Monte Carlo button results in an examination of the filter using a user-specified percentage plus/minus random parts distribution. Worst-case values are clearly shown.
  
  
• Items that are probably going to be used "globally" (on all bands, for a given installation) are stored in a Global Default file and are read into the program at startup. These can be edited and saved by the user. Examples of the items stored in the global defaults file are system impedance (50?), inductor Q values (200?), capacitor Q values (2000?) and so on.
  
  
• For maximum quality of printed output, the output to the printer is not a "screen dump" but instead is from a routine which writes directly to the printer. The quality of that printout will be limited only by that printer, commonly several hundred pixels per inch. The printer output on one sheet contains the schematic with parts values along with the plot of responses and essential design information.
  
  
• Click on the "Elsie" button to write a file to drive Elsie the filter design and analysis program for followup filter examination in even greater detail.
  
  
• Click on the "LTspice" button to write a ready-to-run LTspice file to drive the LTspice simulator for further examination, especially involving component voltage and current stress issues.
  (Tonne Software has no connection with Linear Technology Corporation.)