NAME
xsmc - An X Smith Chart Calulator for RF impedance matching
SYNOPSIS
xsmc [ -h ]
DESCRIPTION
xsmc is a X application that allow to do all the calculation usually
done on a Smith Chart. It permits to make calculation for network
composed by resistor, capacitor, inductance, and trasmission (also as
stub). Network topology is limitated to series, parallel and as
trasmissive for trasmission line. No series connection are allowed in
parallel branch, neither parallel connection in series branch.
Trasmission 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 initial impedance to be
match, 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.
The initial (start) impedance is thought as "the load" so when adding a
trasmission 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
-h A little help.
INTERACTIVE COMMANDS
xsmc dosn’t have menu or such simple command explained in its windows,
since it’s intended for an exentesive use where several repetitive
command has to be issued during a session. So nearly all the command
has to be issued as a single keystroke. This is, in the author’s
opinion, the preferable way for very specialistic programs that has to
be used exetensively.
q Quit the program.
1 Toggle visualization of impedance (Z) circle
2 Toggle visualization of admittance (Y) circle
3 Toggle visualization of reflection coefficient (RHO) circle
4 Toggle visualization of constant Q circle
s Set start point
z: set start point as impedance
y: set start point as admittance
r: set start point as refletction coefficient
0 (zero)
Set characteristic impedance z0
f Set frequency (f0)
a Add a network element (see dialog window explaination):
r: add a resistor
l: add an inductor
c: add a capacitor
t: add a transmission line or stub
i Insert a network element before the highlighted element, as in
’a’
d Delete the currently highligthed element
Curs Up
Highlight previous element
Curs Down
Highlight next element
Curs Left
Decrease the first field of currently highlighted element
Curs Rigth
Increase the first field of currently highlighted element
Shift+Curs Left
Decrease the second field of currently highlighted element
Shift+Curs Rigth
Increase the second field of currently highlighted element
Page Up
Increase the tuning increment
Page Down
Decrease the tuning increment
w Write network file:
s: spice format
r: RFCS format (to be implemented, when RFCS will exist)
= Change first field and placement of currently highlighted
element
*** Of future implementation ***
o Start optimization, ESC to stop.
l Lock currently highlighted element for optimization
p Print smitchart on a postscript file
DIALOG WIN
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
given.
(see below) separated by a space.
s Series placement
p Parallel placement
t Trasmission line placed in trasmissive mode, i.e. as a
quadrupole
o Open parallel stub
c Short parallel stub
a Open series stub
l Short series stub
DATA PRESENTATION
The single window of xsmc 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 dialog portion in the lower right portion, where data are
introduced.
EXAMPLE OF USE
Let’s try a simple example to understand how xsmc 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 in the dialog
win the string ’f0’ appear; since the data requested is a single number
the middle line is unused, and in the bottom line the frequency can be
introduced. Type the string ’15.5M’ and then enter. Now in the vertical
bar the frequency entered is displayed.
Next set the start point impedance: press ’s’ and in the dialog win top
line appear the title "Start Point"; in the middle line the choices "Z
Y Rho" are displayed, so press ’z’ to insert starting point as
impedance. The choices’ string are substituted by the actual choice,
that’s ’z’. Now the impedance can be entered as the string small oval
(3x2pixel!).
The network has now to be constructed, use ’a’ command to add elements
to network. Let start with a series inductance of 800nH, so press ’a’
and then chose ’l’, next introduce the value as ’800n s’ and enter that
means 800nH placed in series. This value is really too large, use left
cursor to reduce a bit. Up to where? Let’s help you displaing the
admittance constant circles pressing ’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 ’a’
then ’c’ and now insert the string ’200p p’. Now the admittance circles
may confuse, remove it by pressing ’2’ again. The value of 200pF is too
small, enlarge it by pressing the 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 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 PageDown and the "tunestep" value shown in
the vertical bar is reduced from 10% to 5%, try again to use curors
left and right. 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 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 (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 to arcs ends you can see that
the point has an impedance of about 10+j20ohm.
Trasmission 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 to parameter, the
electrical lenght and the caracteristic impedance: the former can be
adjusted with cursor left/rigth as for resistor, inductance and
capacitor; the latter can be adjusted with Shift+cursor left/right. For
introducing parameter for transmission line the string to be entered in
the bottom line of dialog win must be
"<electrical length [deg]> <characteristic impedance> <placement>".
Now the network can be saved pressing ’w’: actually only spice format
is supported, so type ’s’ and than enter a valid filename, e.g.
’net1.cir’. The file so generated can be now analized with spice
simulator; maybe you are intereste in simulating it sweeping arround
15.5MHz, so modify the line
.ac lin 1 15.50MEG 15.50MEG
in
.ac lin 51 10MEG 30MEG
and run spice.
FILES
xsmc dosen’t need any (configuration) file. File describing the
network currently analized can be generated, it’s only needed that a
minimum file permission is allowed, if not the program can, however
work, but data cannot be saved.
SPECIAL FILES
xsmc dosen’t need any special file (such as fifos, etc...).
ENVIRONMENT
xsmc dosen’t care about environment.
LIMITATIONS
Porting can be very very difficult, since all is based on X windows
programming, but for other platform a plenty of similar program are
available, free and good one too.
BUGS
· When in dialog window if resizing or other windows signal occour the
dialog session is aborted
Help me to find more.
TODO
In order of importance and urgence:
· Automatic optimization function, comprising a target settting (not
alwais one want to match to z0) and a component locking.
· Postscript printing of chart and arcs.
· Cursor in the dialog window.
· 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
packet radio: ik5nax@ik5skv.#fi.itos.ita.eu
website: www.qsl.net/ik5nax
SEE ALSO
spice3(?)