Feed-Lines & Impedance Matching

• Balanced Line-Zin Input Impedance of Balanced-Pair Transmission Lines Terminated with a Load This program is a companion to Input_Z which deals with coaxial lines. The input impedance of a transmission line is often needed. Much experience is required just to guess what it might be. This program accurately calculates it ...
• Balanced Lines 4 Balanced, Twin-Conductor Transmission Lines, 20Hz to 1GHz This program analyses the performance of a variety of balanced lines from lines with very wide-spaced, large-diameter, bare conductors for power distribution, via HF ladder-line antenna feeders, to figure-of-8 and oval plastic-insulated types. There are also the various overhead open-wire and paper-insulated underground forms of construction used in telephone and digital networks. At the UHF end of the spectrum there are receiver input tuned lines 1 or 2 inches long. Large diameter tubes are used as tank circuits in high power VHF transmitters ...
  
  Also see these earlier versions of this program:
  
  
  • Balanced Lines 1 Balanced-Pair, Open-Wire, Transmission Lines, 16Hz-1Gz This form of transmission line has been in use since the earliest days of the electric telegraph. When the telephone was invented a long-distance network of low attenuation, balanced pair, overhead lines was already in existence. There was a rapid world-wide telephone expansion. Simultaneously the distribution of electric power within towns and into the countryside began using lines of the same type. They are still widely used. This program will investigate behaviour of lines at power frequencies. It will also show that a pair of wires, diameter = 4mm (0.16"), spaced at 300mm (12"), Zo = 600 ohms, allowed phone calls at distances of 1000kM (620 miles) or more, long before the age of electronic amplifiers ...
    
  • Balanced Lines 2 Introduction to Balanced-Pair Transmission Lines, 20Hz-500MHz This program analyses the behaviour/performance of a variety of balanced lines from very wide-spaced bare conductors to figure-of-8 plastic insulated types, from power frequencies up to UHF, when terminated with any impedance between a short and open circuit. To specify the line the only dimensions required are conductor diameters and length. Shapes and sizes of insulators and spacers are incorporated indirectly via the resulting impedance (Zo) and velocity (VF) ...
  • Balanced Lines 3 Balanced-Pair Transmission Lines, 20Hz to 1GHz This program is a modified version of Balanced Lines 2. Essentially, program input is a line specification including Zo and length, and a user-defined terminating impedance Zt = Rt+jXt. Line input impedance Zin = Rin+jXin is then computed ...
    
    
• Balun Transformers Toroidally-Wound Transmission Line Transformers with 1-to-4 Impedance Ratio The analysis applies to bi-filar wound transformers having an impedance step-up ratio of 1-to-4. The low impedance winding is always unbalanced to ground. The high impedance winding may be unbalanced, or balanced with grounded centre-tap. The winding consists of two insulated wires laid alongside each other to form a short balanced-pair transmission line. The twin line is wound round the ferrite core and becomes an RF choke insofar as longitudinal currents are concerned ...
• Behaviour of Coil Line The Behaviour of a Single-Layer Solenoid Coil as a Transmission Line All conductors possess inductance and have capacitance to their environment. Series L and shunt C are distributed along their length. The inductance due to a coil winding is added to the inductance of a solid cylinder of the same diameter and length of the coil. The distributed capacitance of the coil is the same as that of the solid cylinder provided the turns are not spaced too wide apart. L and C can be estimated mathematically from coil dimensions ...
• Coax Line Input Z The Input Impedance of a Coaxial Transmission Line Terminated with a Load This program is a companion to Line_Zin which deals with balanced lines. The input impedance of a transmission line is often needed. Much experience is required just to guess what it might be. This program accurately calculates it ...
• Choke Balun Design & Performance of a Choke Balun Plus Balanced Transmission Line A choke balun is a pair of wires wound alongside each other around a ferrite core. The two wires together form a single-conductor choke, simultaneously behaving as a two-wire balanced transmission line. The choking action allows two different circuits to be connected together via the line without regard to the grounding arrangements of either. At one end of the balun can be an unbalanced circuit with one terminal grounded. At the other end the circuit can be floating relative to ground or it can be held firmly balanced against ground ...
• Coax Choke Self-Resonant Frequency of Single-Layer Solenoid Coils Coils have a distributed self-capacitance equivalent to a lumped capacitance connected between its ends. Consequently, all coils have a parallel resonant frequency. At resonance there's a very high impedance between the ends of the coil. A common application is use of a coil as a resonant RF choke ...
• Coax Line Coaxial Transmissions Lines, 50Hz to 1GHz This program allows the user to specify/design a coaxial line, to compute the line's principal characteristics, to terminate the line with any complex impedance between open and short circuit and obtain the line's input impedance. Performance is computed in terms of reflection coefficients, VSWR and actual transmission efficiency. The line's matched loss is displayed for comparison ...
• Coax Radiation Centre-Fed Dipole - Radiation from Coaxial Feedline The effect of 'unintentional' radiation from an antenna feedline are small changes in the radiating pattern. Signal, noise and interference levels, will be affected in random unpredictable directions. The effects on station operating performance will differ between sites. The most noticeable change will be partial filling-in of a null in the pattern which may be judged either useful or highly undesirable ...
• Coax Rating Power Rating of Solid-Polyethylene-Insulated Coaxial Cables This program assists with selection of dimensions of RF coaxial cables when input power is high enough to cause concern about the temperatures to which plastic materials may be subjected. It will also assist with estimating the power rating, Zo and attenuation of a cable when nothing is known except its radial dimensions. Results are valid from 0.5 to 1000 MHz at temperatures up 150 degrees Celsius ...
• Coax at VLF Behaviour of Coaxial Transmission Lines at Low Frequencies At decreasing frequencies, when conductor inductive reactance becomes less than its resistance, the magnitude of line impedance Zo increases rapidly and the angle of Zo becomes progressively more negative. At power frequencies Zo is an order of magnitude greater than its HF value and its angle nears -45 degrees. From its constant value at HF the propagation velocity decreases to a low value which complicates fault-locating techniques which depend on a knowledge of the velocity factor. In general, things begin to happen at frequencies less than several hundred kilohertz ...
• Coil as a Transmission Line Behaviour of a Solenoid Coil as a Transmission Line There is a short vertical antenna less than 1/4-wavelength in height. It is loaded at the bottom end with a single-layer solenoid-wound coil. The top section is a vertical rod or wire. Both the coil and rod are considered to be transmission lines ...
• Connector Impedance Mismatch Effect of Impedance Mismatch of Coaxial Connectors on System Performance This program calculates the degradation in system performance caused by insertion of a length of transmission line of different impedance to system Zo. It is applicable to either balanced or coaxial transmission lines...
• End-Fed Half-Wave Antenna Tuner Tuner Design for Half-Wave Vertical & Similar-Length End-Fed Antennas It is sometimes difficult to match end-fed antennas with high feedpoint impedances, to low impedances such as 50 ohms. This tuner is intended to match to match end-fed half-wave vertical and inverted-L antenna wires to low impedance coax lines and transmitters with high power-transfer efficiency ...
• L-Network Calculate the Terminating Impedance of an L-Match Network The generator is connected to the left-hand terminals. The termination is connected to the right-hand terminals. Computed values of Rt and Xt are those which cause a network's input impedance to match the generator's internal resistance. When terminated with Zt there is a conjugate match at a network's output terminals and maximum available power is dissipated in Rt...
• L-Tuner Impedance Transforming L-Networks Both networks A and B transform the load impedance RL + jXL to Rin + jRin. If RL > Rin then network A applies. If Rin > RL then network B applies. Series reactances Xs and parallel reactances Xp can be either coils or capacitors. Sometimes both components in a network may be of the same L or C type ...
• Line Characteristics Calculate Line Characteristics from Open & Closed Impedance Measurements Input impedance measurements on a transmission line with the remote end open-circuit and then with the remote end short-circuit provide enough information from which to calculate the line's impedance Zo, the angle of Zo and overall attenuation in dBs. When line length is known the inductance, capacitance, conductor resistance and conductance of the insulating material per unit length can also be calculated together with propagation velocity ...
• Load Z from Input Z Compute Load Impedance from Measured Input Impedance for any Length & Zo The input impedance of an inaccessible radio antenna can by obtained by calculating what it must be to give the impedance measured at the input end of the antenna's feed line ...
• Matching Section Impedance-Matching Section of Line Inserted in Antenna Feeder This program assists with design of a class of impedance-matching transformers formed by inserting a short section of line, of different Zo, into the feedline between transmitter and antenna. It is applicable to both coaxial and balanced-pair lines. To minimise loss due to standing waves the matching section is best located near the antenna end of the feeder. But in principle it may be inserted anywhere along the length ...
• Phase Shift Networks Symmetrical T & Pi Phase Shift Networks This program assists with the design of T and Pi, coil and capacitor networks used to set the relative phases of currents flowing in the various elements of radio antennas. Such arrangements are used in both receiving and transmitting modes to control beam bearings as an economic alternative to rotation of large antenna arrays ...
• Standing Waves Exact Calculation of Standing Waves on a Mismatched Transmission Line This program models making measurements of volts and amps along a trans-line. The input impedances looking in both directions from D are also measured. From this data various other parameters of interest are calculated. Exact classical transmission line formulae are used. Results are exact to the number of digits displayed. For SWR2, slide D in fine increments to find max and min of V and I ...
• Stub Tune Match Antenna Zin to Feedline Using a Stub-Line Transformer LineA and LineB have the same Zo. Both lines are less that 1/2-wavelength. The feedline from the transmitter can have any Ro and be of any length. Velocity factors of LineA and LineB are assumed unity which applies only to air-spaced lines. Physical length of other types must be calculated outside this program ...
• SWR Argument Transmission Line + Antenna + Two SWR Meters Contains factual argument backed by software analysis that SWR Meters should be renamed TLI. (Transmitter Loading Indicators) ...
• SWR Meters Design, Calibration & Performance of Standing-Wave-Ratio Meters An SWR meter is a fixed-ratio resistance bridge. The external "unknown arm" is the input impedance, R+jX, of the antenna system. The bridge unbalance voltage is displayed on a meter calibrated to indicate a choice of system parameters ...
  
  
  • Part 2 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Basic Meter & Voltmeter Circuits R1 & R2 is a voltage divider across the load. Fraction K = R2/(R1+R2). Voltage across R3 is load current times R3/N which can be switched either to add to or subtract from the fraction K. When subtracting the meter responds to reflected waves and when adding it responds to forward waves. The calpot is adjusted for a voltmeter null for reflected waves when ZL equals reference resistance Zo ...
  • Part 3 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Toroidal Current Transformer Example & Estimating Transmitter Resistance The ferrite ring core is of a size which when wound with 24 AWG wire can be slipped over the coaxial polythene insulant. Typical dimensions: OD=1/2"=13mm. ID=1/4"=7mm. Thickness 1/6"=4mm. With a permeability of 200, 1uH needs 3.4 turns. 15 turns gives 19.5 uH which has a reactance of 220 ohms at 1.8 MHz. A 33-ohm shunt resistor gives a satisfactory reactance to resistance ratio of 6.7 This transformer would be suitable for a 30 to 100 watt, 50-ohm SWR meter ...
  • Part 4 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - More Notes Ideally, the ferrite core of the current transformer should have a permeability large enough to need only one turn on the primary winding. The single turn is then the inner coaxial conductor plus polyethylene with a short gap in the braid. The gap in the braid should be no longer than is necessary to obtain a connection from the inner conductor to the voltage divider. Stray capacitance between the exposed inner and the secondary winding can be included in the divider chain with careful layout. A frequency range from 1.8 to 30 MHz should be possible ...
  • Part 5 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Calibration Procedure The program performs this procedure automatically after design parameters have been entered and the circuit completed. The procedure modeled is as follows ...
  • Part 6 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Measuring Errors SWR meters function correctly only when used in transmission systems having a Zo for which they have been designed. Meters and Zo's are not interchangeable ...
  • Part 7 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Direct Indications of Reflection Coefficient and SWR, and Obtaining Simultaneous Display of Forward and Reflected Power As already described, when the source impedance as seen looking back towards the transmitter from the meter is not Zo, the indicated values of RC and SWR are incorrect but the true values can be calculated from forward and reflected watts ...
  • Part 8 - Design, Calibration & Performance of Standing-Wave-Ratio Meters - Location of Current Transformer, Operating Reminders, and Software The circuit diagram shows the current transformer in series with the source. To make internal source resistance exactly equal to Zo, deduct the transformer's input ohms from Zo before entering source resistance into the program. Insofar as the source is concerned the voltage divider impedance is in shunt with the load ...
• T-Networks Impedance Transforming T-Networks - Antenna Tuner Application For given input resistance, load impedance and frequency the program computes the values of C1, C2 and L. For given coil Q, capacitor Q and RF power input, the power dissipated in each of the 3 components and overall efficiency is computed, together with the peak voltages across C1 and C2 ...
• T & Pi Networks T & Pi Impedance Matching & Phase Shifting Networks This program simultaneously computes component values for both the T and Pi networks to match any two resistive terminations and having a specified value of phase shift between output and input terminals. For both T and Pi networks there are two versions - phase lagging and phase leading. Thus there are four networks displayed from which to select for the required purpose ...
• Two Lines Input Impedances of Two Cascaded Transmission Lines with a Load Transmission lines are impedance transformers. For a given terminating or load impedance this program calculates the input impedance of a line. Line lengths are specified in terms of wavelengths at the line's own velocity. To obtain greatest accuracy when calculating it is desirable to take line loss into account ...