Ubuntu Manpage: gsmc - A GTK Smith Chart Calulator for RF impedance matching

NAME

       gsmc - A GTK Smith Chart Calulator for RF impedance matching

SYNOPSIS

       gsmc

DESCRIPTION

       gsmc  is  a  GTK application that allows one to do all the calculation usually done on a Smith Chart.  It
       permits one to make calculation for network composed by resistor, capacitor, inductance, and transmission
       line (also as stub).   Network  topology  is  limitated  to  series,  parallel  and  as  trasmissive  for
       transmission  line.  No  series connection are allowed in parallel branch, neither parallel connection in
       series branch.  Transmission line can be placed as quadrupole or as a parallel  or  series  stub,  either
       opened or shorted at the other end.

       Calculation  procedure starts with setting the initial impedance to be matched, next network elements are
       added and tuned to obtain the desidered impedance value.

       The network so obtained can be saved in spice format for other analisys; current work can  be  saved  for
       succesive retrieve.

       The  initial  (start)  impedance  is thought as "the load" so when adding a transmission line placed as a
       quadrupole rotation is clockwise, going "toward generator"; generator is placed after  the  last  network
       element, as can be seen from spice output.

OPTIONS

       None

INTERACTIVE COMMANDS

       gsmc  is a menu based GTK application with as much as possible accelerators and mnemonics. Nearly all the
       command can to be issued as a single keystroke or keystroke with modifiers.  This  is,  in  the  author's
       opinion, the preferable way for very specialistic programs that has to be used extensively.

       Ctrl+q Quit the program.

       Ctrl+1 Toggle visualization of impedance (Z) circle

       Ctrl+2 Toggle visualization of admittance (Y) circle

       Ctrl+3 Toggle visualization of reflection coefficient (RHO) circle

       Ctrl+4 Toggle visualization of constant Q circle

       s      Set start point: can be entered as impedance, admittance or reflection coefficient

       Ctrl+0 (zero)
              Set characteristic impedance z0

       f      Set frequency (f0)

       r      Add a resistor

       l      Add an inductor

       c      Add a capacitor

       t      Add a transmission line or stub

       Shift+r
              Insert a resistor before the highlighted element

       Shift+l
              Insert an inductor before the highlighted element

       Shift+c
              Insert a capacitor before the highlighted element

       Shift+t
              Insert a transmission line or stub before the highlighted element

       d      Delete the currently highligthed element

       Shift+Curs Up
              Highlight previous element

       Shift+Curs Down
              Highlight next element

       Shift+Curs Left
              Decrease the first field of currently highlighted element

       Shift+Curs Rigth
              Increase the first field of currently highlighted element

       Mod+Curs Left
              Decrease the second field of currently highlighted element

       Mod+Curs Rigth
              Increase the second field of currently highlighted element

       Mod+Curs Up
              Increase the tuning step

       Mod+Curs Down
              Decrease the tuning step

       Ctrl+w Write network file in spice format

       Ctrl+n Restart for a new calculation with a clean chart

       =      Change first field of currently highlighted element

       Mod+=  Change second field of currently highlighted element

       Ctrl+a Start autotune procedure (tune goal is characteristic impedance)

       Ctrl+x Toggle lock flag in autotune procedure

       Ctrl+p Write an EPS or PS file

       Ctrl+l Load a previously saved .B gsmc job

       Ctrl+l Save a .B gsmc job

       Ctrl+f Increase frequency

       Shift+Ctrl+f
              Decrease frequency

       Check online keystroke for an updated list of commands.

       DIALOG WIN

       For  operation  that  requires  data entry a widget is created; it is composed by an text entry field and
       optionaly some radio button to chose the format of data entry.

       The format for data entry can be a single number, or a more complex string. First of all every number can
       be supplyed using standar prefix for unit of measure i.e.:

              a      (atto) 1e-18

              f      (femto) 1e-15

              p      (pico) 1e-12

              n      (nano) 1e-9

              u      (micro) 1e-6

              m      (milli) 1e-3

              k      (kilo) 1e3

              M      (mega) 1e6

              G      (giga) 1e9

              T      (tera) 1e12
       Note that for spice output format mega is written as MEG instead of M, that will be otherwise  recognized
       by spice as milli.  Unit of measure are not allowed to be in the text entered.

       Where  a  complex number is required both the rectangular and the polar format are recognized: the former
       can be supplied as '12.3-j456m' while the latter can be supplied as '34.2 145' meaning a modulus of  34.2
       with  a phase of 145 degrees. If the complex number is purely immaginary only something like 'j82' can be
       supplied, while if immaginary part is zero a single number can  be  given.  Immaginary  operator  can  be
       issued as 'i' as well as 'j'.

DATA PRESENTATION

       The single window of gsmc is divided in four parts:

       -      The Smith chart itself in the upper left portion, where arcs and constant circle are drawn.

       -      The  vertical  bar  on the rigth of the Smith chart, where initial, final and cursor impedance are
              presented togheter general data.

       -      The horizontal bar on the bottom of Smith chart where the network element are listed.

       -      The portion in the lower right portion, for future use...

EXAMPLE OF USE

Let's try a simple example to understand how gsmc work. Suppose to have a load of 10-j35ohm to be matched
to 50+j0ohm at an operating frequency of 15.5MHz and we can use only concentrated reactive elements, i.e.
inductances and capacitors.

So start with setting operating frequency: press 'f' and a dialog win will appear. Type in the string
'15.5M' and then press enter. Now in the vertical bar the frequency entered is displayed.

Next set the start point impedance: press 's' and a dialog win will appear with the title "Start Point";
select the format for start point either clicking the "Z" radio buttono or using the menmonic via Mod+Z.
Now the impedance can be entered as the string '10-j35' followed by enter. The starting point is now
displayed as a small circle.

The network has now to be constructed: let start with a series inductance of 800nH, so press 'l' and next
introduce the value as '800n', be sure that "Series" radio button is selected before pressing enter. TAB
and Shift+TAB is useful to move across items in dialog win without leave hands from keyboard. This value
is really too large, use Shft+Left cursor to reduce a bit. Up to where? Let's help you displaing the
admittance constant circles pressing "Ctrl+2", the arc should arrive to the G=1 circle (also called the
mirror circle), it's arround 546nH.

Now add a capacitor in parallel connection, saying of 200pF: press 'c' and insert the string '200p' and
select Parallel either with mouse or with "Mod+p". Now the admittance circles may confuse, remove it by
pressing "Ctrl+2" again. The value of 200pF is too small, enlarge it by pressing Shift+Left cursor up to
get the end point near to the chart's center. The point reached with 429pF has nearly zero imaginary but
is 43ohm of real part instead of 50ohm.

So back to the inductance and try to modify it, with Shift+Cursor up move to the first component and then
try to change the inductance value by pressing cursor left and right. The changes are too large and 50+j0
cannot be reached. So press "Mod+Cursor down" and the "tunestep" value shown in the vertical bar is
reduced from 10% to 5%, try again to use Shift+Curors left and right. It feel better. Now do the same on
the capacitor, moving to it by pressing cursor down and than adjusting value as for the inductance.

Final values should be arround 568nH and 408pF. Now you want to see what appen using the closest standard
commercial values, that is 560nH and 390pF in the E12 series. Select (with Shift+Cursor Up), if needed,
the inductance and then press '=', the dialog window appear (middle line is unused) and the string '560n
s' has to be introduced. Next move to capacitor (Shift+Curs Down) and pressing '=' here insert '390p p'.
The final result is of SWR=1.14, if it's enough for you...

Moving the mouse to the point where the two arcs ends you can see that the point has an impedance of
about 10+j20ohm.

Transmission line and resistor can be used similary refer to the section INTERACTIVE COMMANDS for knowing
how they can be placed. The major difference with transmission line is that they have two parameter, the
electrical length and the caracteristic impedance: the former can be adjusted with Shift+Cursor
left/rigth as for resistor, inductance and capacitor; the latter can be adjusted with Mod+cursor
left/right.

Now the network can be saved either in a gsmc format (.gdt extension) by pressing Ctrl+s or in spice
format pressing Ctrl+w: The file so generated can be now analized with a spice simulator or gnucap or
ngspice ; maybe you are interested in simulating it sweeping arround 15.5MHz, so modify the line

.ac lin 1 15.50MEG 15.50MEG

.ac lin 51 10MEG 30MEG

and run spice or gnucap

This example should be included in gsmc package an can be retrieved by pressing Ctrl+l and selecting
example1.gdt.

Autotune algorithm is very primitive and may not reach what is very simple to do by hand, do not ask to
much from it, work in progress...

Charts so drawed can be printed to a Postscript or Encapsulated Postscript file; in printed file some
information are added on the chart drawing as well as Circuit Description and some of the Current Value
are transcripted. Automatic recognition of filename extension .eps or .ps allows one to specify if the
file has to be in encapsulated format or not.

FILES

       gsmc don't use special configuration file, a gtkrc file is supplied and can be tuned to user preferences;
       if present it must be in /root/.gsmc/gtkrc.  File  describing  the  network  currently  analized  can  be
       generated,  it's  only needed that a minimum file permission is allowed, if not the program will work but
       data could not be saved.

       Data file (.gdt) contain a copy of internal  data  structures  in  a  quite  human  readable  format;  by
       inspection  one  can recognize and modify some parts using a text editor. For more details compare a .gdt
       file with smcdata struct defined in source file main.h.

LIMITATIONS

       Porting can be very very difficult, since all is based on X windows programming and GTK library, but  for
       other platform a plenty of similar program are available, free and good one too.

BUGS

       Help me to find.

TODO

       • Improve autotune algorithm

       • Target settting (not alwais one want to match to z0) for autotune.

       • Auxiliary window for error reporting instead of stderr.

COPYING

       This  program  is  free  software;  you  can  redistribute it and/or modify it under the terms of the GNU
       General Public License as published by the Free Software Foundation; either version 2 of the License,  or
       (at your option) any later version.

AUTHOR

        Lapo Pieri  (IK5NAX)

        Home address: via A. dei Corbizi 9  I-50127 Firenze Italy
        Phone: +39 055 410209
        e-mail: ik5nax@amsat.org, lapo_pieri@virgilio.it
        website: www.qsl.net/ik5nax