home *** CD-ROM | disk | FTP | other *** search
- DOCUMENTATION FOR THE DIGITAL SMITH CHART PROGRAM `SMITH' BY AA4L
-
- Smith calculates resistance and reactance at any point along a
- transmission line. It also calculates reflection coefficient `rho'
- and vswr.
-
- Resistance and reactance as measured at some point on the transmission
- line are entered in response to prompts. The program then calculates
- R & X for each n degree point for the next half wave length TOWARD THE
- GENERATOR. `n' is user selectable. Values for points toward the load
- may be derived indirectly as follows: Assume that a transmission
- line is 230 deg long, and that R & X have been measured at the trans-
- mitter end. It is desired to find the R & X at the antenna. Since all
- values are the same for each half wave length of a (lossless) line,this
- line is equivalent to a line which is 230 -180 = 50 deg long. Hence
- the R & X at the antenna is equal to the R & X at a point 180 - 50 or
- 130 deg toward the hypothetical generator from the point at which the
- measurements were taken. Think about it!
-
- The equivalent of a Smith chart gamma swr circle may be created by
- asking for a listing for a line which has a known point of R=swr*Z0
- or R=swr/Z0 and j0.
-
- Conductance `G' and susceptance `B' are also calculated for each n
- degree point. This data is very useful for the calculation of
- parallel matching stubs.
-
- To avoid divide by zero errors, enter R=0.000001 or such for a shorted
- line and R=999999 or such for an open line. Values near 90 deg are
- somewhat invalid under some conditions. (The tangent of 90 deg is
- infinite.)
-
- The following formula is used by SMITH to calculate physical line
- lengths: theta = length in ft * 0.367 * freq in mhz / velocity factor.
-
- 73 es gl de AA4L Bob Johnson 11305 Rums Hill Raleigh NC 27614
- 919 847 5606 10/10/82
-