Computer Program for Determining the Effects of Transfer Functions on a Pulsed RF Signal

In EMC studies one often wishes to determine the effect of a pulsed RF signal on a receiver which is tuned off the signal center frequency. Measurements of pulsed spectra are made by means of spectrum analyzers and field intensity meters. However, there exists some confusion about the shape of the resultant pulse at the output of the IF amplifier of a receiver which is off-tuned from the pulsed signal. In order to properly interpret the effects of pulsed signals on receivers and to interpret the readings of spectrum analyzers and field intensity meters, it is necessary to determine the envelope of the waveform at the input to the detector. These waveforms can be calculated by convolving the input time waveform of the receiving device with the time domain transfer function of the receiver up to the detector. However, it is extremely difficult to obtain the mathematical form of the time domain transfer function of a receiver. However, use is made of the relationship that the LaPlace or Fourier transform of convolution is equal to the frequency domain multiplication of signal and transfer function. A computer program for obtaining the Fourier transform of most time waveforms including RF pulses has been written. The program integrates the time waveform by straight line segments between the sampled points on the time waveform. The frequency domain transfer function of cascaded tuned amplifiers is used to simulate the receiver.