Untitled Document

S-18 Transmission Line Trainer (50-1300MHz)

** Impedance matching designed by Prof Girish Kumar, Dept of Elect Eng, IIT Bombay, India
Laptop shown above is not included

Experiment & Study Areas
•	Standing Wave Patterns upto four patterns at a time
•	Complex Impedance measure R+jX
•	SMITH Chart Auto and Manual
•	Study Relationship of VSWR, shift in minima, reflection co-eff for
	Case 1: Matched Line
	Case 2: Open-Circuited Line
	Case 3: Short-Circuited Line
	Case 4: Inductive (nonresistive) Load
	Case 5: Capacitive (nonresistive) Load
	Case 6: Resistive Load > Zo
	Case 7: Resistive Load < Zo
	Case 8: Resistive-Inductive Load
	Case 9: Resistive-Capacitive Load
•	VSWR, V(i), V(r) vs FREQ
•	Impedance Matching
•	Impedance Variation along mismatched line
•	Insertion Loss
•	TDR (Time Domain Reflectometer)
•	NETWORK / SPECTRUM Analysis

Brief Description & Key Specifications

setup

STS-3033 Software Features ...

click picture Standing Wave Pattern	click picture Four Standing Wave Patterns	Standing Wave Patterns Standing Wave Patterns are generated depending on the type of load terminating the transmission line. Up to four standing wave patterns can be obtained for concurrent study. Voltage as well as Current SWR patterns can be measured.

click picture	Complex Impedance (R+jX) Measurement Complex Impedance measurement requires two Standing Wave Patterns, one with the line terminated in a short and the other with the unknown load. Computations based on the linear difference between the minima of the two patterns (Xvm) and the VSWR of the Unknown Impedance, will yield the values of R+jX of the Unknown Impedance. The picture on the left shows the measurement of Xvm, calculation based on the entry of Frequency, Xvm, and VSWR to yield the values of R & jX; and plotting the point on the Smith Chart using the manual mode.

click picture	Smith Chart - Auto (Vector Network Analysis) Automatic measurement and plotting of the Smith Chart is possible using the Auto Smith Mode from 450 to 1300MHz. The plot starts at 450MHz with a Blue Square. Subsequent points at 500MHz to 850MHz are plotted in Red Dots and joined by a line. In the above plot the VSWR is less than 1.3 at 800MHz. (DUT is a Quad Antenna)

click picture	Impedance Matching Impedance Matching is essential for maximum power transfer to a load. An ideal load would be 50+j0 ohm. However real life loads (R+jX) require matching networks to transform them as close to the ideal as possible, where VSWR 1.0 (generally VSWR <2 is acceptable) A user can fully understand what impedance matching implies and get a theoretical and experimental feel of the matching process.

click picture	VSWR vs Frequency Mode This mode is useful for the study of Incident Voltage (Vi) & Reflected Voltage (Vr) of a device under test (DUT) and computation of VSWR vs Frequency DUT shown is a 800MHz QUAD Antenna connected via the Directional Coupler. The Plots are taken over the 750 - 850 MHz freq range. The user can locate the minimum VSWR to identify the resonant freq of the antenna. The VSWR is measured as 1.015 at the resonant frequency of 810.5MHz.

click picture	Insertion Loss (Scalar Network Analysis) The user can measure the Insertion Loss or thru loss of a passive device or measure gain of an active device of, say an amplifier. The start/stop frequency and the no. of steps are to be selected. Initially the RF output is measured and stored by the software. The DUT is then connected and the measurement is normalized against the stored values and the Insertion Loss (or gain) vs Frequency is plotted. Two cursors give readout of Frequency and dB Loss. A text file of Freq & Loss can be saved.

click picture	Impedance Variation along mismatched Transmission Line When there is a mismatch, the impedance will be alternatively higher and lower than the Zo across the line. The V and I standing waves above have been obtained with a short termination. The Impedance Plot is obtained by computing the V/I at each point and plotting it. Cursor readout of the min & max values is 0.707 ohm & 4566 ohm which agrees with the theoretical values of 0 & infinity .

click picture	Spectrum Analysis In this mode the Frequency Spectrum of an input signal is measured & plotted. The start, stop frequency, no. of steps and step size are user selectable via software

click picture	RF Recorder Mode (Level & VSWR Monitoring) In this mode the RF Signal is connected to the Receiver. Measurement freq is set via the software. The dB level is measured and displayed Digitally and also plotted as a Scroll Graph. The RF Recorder Mode can be used for exploration and behaviour of RF signals in real time.

click picture	TDR (Time Domain Reflectometer) The S-18R TDR is a simple but powerful tool used to evaluate transmission lines. Any oscilloscope having bandwidth >20MHz will display the incident and the reflected pulses. Users can analyze the pulse response and measure time intervals to understand effect of cable terminated in a short, open, characteristic impedance. They can also study velocity factor, attenuation and cable fault location.