Symmetrical T & Pi Phase Shift NetworksAuthor: R.J.Edwards G4FGQ © 7th January 1999
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.
L & C network component values depend on the radio frequency, the terminating resistance and on the required phase shift in degrees. Individual networks may be connected in cascade - total phase shift being the sum of the individuals. This allows different valued networks to be switched in and out of circuit to obtain any desired total value of shift. 90 degrees is the greatest value computable by this program. This is usually the greatest value required from a single network.
A 90 degree network also behaves as an impedance transformer. It will match a pair of system resistances, R1 and R2, when its own resistance is Sqrt(R1*R2).
Phase-lag or phase-lead networks are equally effective. Preference depends on whether advantage is to be taken of their high or low-pass filtering actions.
All networks covered by this program are symmetrical and bi-directional.
Phase shift networks are usually placed in coaxial transmission lines to the antenna elements. The system impedance to be entered in the program will then be a low impedance of 50 or 75 ohms. This may result in inconvenient values of inductance and capacitance at the lower frequencies. So a higher value of 200 or 500 ohms may be chosen which will require an impedance transformation. Choice of impedance may also be influenced by RF power level and component ratings.
Delay or Pulse-Forming Artificial Lines
A chain of small-value, identical, phase-lag networks also forms an artificial delay line which may be used with analogue or digital waveforms. The delay in nanoseconds of a single Pi-section is computed. Total delay is proportional to the number of sections. To minimise waveform distortion, the cut-off frequency of the equivalent low-pass filter should be higher than any significant frequency component contained in the waveform. This is achieved by using a large number, say 15 or 20, small-delay networks in tandem.
There are two sets of output data. Use key 'T' to toggle between L and C values in micro-henrys and pico-farads, or component reactances in ohms.
Run this Program from the Web or Download and Run
it from Your Computer
This program is self-contained and ready to use. It does not require installation. Click this link PhaseNet then click Open to run from the web or Save to save the program to your hard drive. If you save it to your hard drive, double-click the file name from Windows Explorer (Right-click Start then left-click Explore to start Windows Explorer) and it will run.
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