RF Design Programs - more information

by Jouni Verronen, OH8RO

LP or HP filter and matching circuit calculation
Three element pi-circuit for lowpass, Y-circuit for highpass
Calculates circuit components, attenuation and return loss. Q can be tuned.
Read notes on CaMF

General impedance calculations, LC circuits calculations
Read textfile CaLC, which describes, how to use it, with examples.

RX front-end IMD and noise figure calculations
This is a set of three calculation programs useful in RX front-end development.
  • IMD program calculates third order input intercept point from two generator measurement. If an individual stage is studied, its gain can also be given to get the output IP3.
  • Noise floor is calculated for given noise figure and bandwidth. Instead of noise figure (NF) noise temperature (T) can alternatively be given. In each case the other value is calculated.
  • NF and T are calculated from so called Y-ratio measurement.
Dynamic range for the RX is also calculated from the IP3 and noise floor results.

Toroidal coil calculations
The program calculates inductances for various toroids and similar cores of ferrous material for the three cases:
  • ordinary closed core toroid,Al-value is known.
  • closed core toroid, relative mu of the material and the dimensions of the core are known.
  • toroid with an air-gap, the length and the area of the core are known
The program can read an ascii text file of toroid information. It can be edited, too.

Wire coil calculations
The program calculates the following inductances made of round wire and located in free air.
  • straight round wire in free space
  • shorted stub made of round wire with rectancular pendings
  • loop with one turn or many turns
  • spiral coil
  • one layer cylinder coil
  • multilayer cylinder coil

Inductance and Q measurement helper program
The program is used to calculate inductance and Q values for a coil from the following measurement:
  • The coil is connected in series with a known capacitor.
  • The circuit is connected over a 50 ohm line between a frequency sweeping RF-generator and a level meter.
  • The frequency and depth of the notch are measured.
If Q-value is not of interest, any kind of measurement for determining the resonant frequency will suffice.

The other part of the program calculates the alteration in turns number needed to resonate the coil - a toroid or a one layer cylinder coil - at another frequency with another capacitor.

Inductance measurement of a coil with parasitic capacitance
This program is intented for measuring low frequency multiturn coils, in which the parasitic parallel capacitance cannot be neglected. The measurement is a notch measurement in a 50 ohm line using two known capacitors.

Quarz crystal calculator
The program is used to calculate the equivalent circuit for a quarz crystal from the following measurement:
  • The crystal is connected in series in a 50 ohm line between a signal generator and a power measuring device.
  • Points for minimum attenuation (series resonance), maximum (parallel resonance) and -3dB are recorded.

Calculated values can then be used in a circuit analysis program for e.g. crystal filter design. The program also has a feature, which is helpful, when one wonders if a crystal at hand is good for a particular crystal oscillator circuit at a certain frequency. One can give any frequency near series resonance, and the program calculates the reactance and corresponding capacitance/inductance values needed to resonate the crystal. Using arrow keys the frequency can be tuned.

Lumped resistor attenuator calculations
The program consists of two parts: synthesis & analysis.
  • Synthesis
    Resistors for T- and Pi-networks are calculated. Also calculates components and loss in dB for the minimum loss L-network.
  • Analysis
    Either T- or Pi-conficuration can be chosen.
    Uses the same terminations as used in the synthesis part. The program calculates insertion loss, port resistances and corresponding return losses for the given attenuator.

Microstrip stub design
This program is for calculating open, short or reactively terminated microstrip stubs. A line can be of constant width or tapered.
There are two operating modes:
  • Program calculates reactance with L and C equivalents seen at the end of the line.
  • The series resonance frequency of the line is calculated.
For tapered microstrips the length of the line is divided to n sections in calculations. For n=1 the line witdths at the ends of the strip are set equal. In this case characteristic impedance Zo and the electrical length of the line at the given frequency is also calculated. Using arrow keys the length of the line can be tuned.

Impedance transform in a transmission line
The program calculates impedance at the end of a transmission line e.g. microstrip or coaxial line, when the terminating impedance is given in series form. The transformed impedance is printed in various forms.

The program was originally made to help in designing matching circuits to UHF transmitters, where the standard practice is to use series microstrips and shunt capacitors. It has a useful feature, that all the input values are tunable using arrow keys. So e.g. line length can be tuned keeping watch when parallel resistance is at the right level. Then also the capacitance value of the shunt capacitor needed can be read right on the screen.

The main program uses electrical parameters for the transmission line, but there is under F2 a subprogram, which calculates those from mechanical parameters if desired (microstrip).
The program has also been used in teaching transmission line properties.
For clarity a Smith Chart shows complex impedances at both ends.

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