Transmitter Models

Simple Transmitter Model

The Simple Transmitter model is convenient when you do not have all the information necessary to model the transmitter in detail; for example, during the system engineering process. The Simple Transmitter Model uses an isotropic, omnidirectional antenna, which is an ideal spherical pattern antenna with constant gain. You can set the following parameters for this model:

Model specs

Frequency is the RF carrier frequency of the transmitter.

EIRP is the Effective Isotropic Radiated Power at the output of the transmit antenna.

Data Rate is the transmitter's data rate, which is a compound dimension with data bits and time as simple dimensions. For example, a data rate entered as 2.5 kb/msec will be converted to 2.5 megabits per second data rate. Valid data bit units are bits (b), kilobits (kb), megabits (mb), gigabits (gb), and terabits (tb). Valid time units are seconds (sec), milliseconds (msec), microseconds (usec), nanoseconds (nsec), and picoseconds (psec). Changing the transmitter’s data rate could affect the values of the Modulator.

Polarization. To specify a polarization model, select Use and select a polarization type. For descriptions of the polarization parameters, see Polarization.

Modulator

STK Communications enables you to select from multiple modulators, including user-defined modulators. Each modulator has a defined modulation. The modulation determines two characteristics:

  • One is the fraction of transmitter power contained within the receiver’s bandwidth, computed in the Bandwidth Overlap Factor.
  • The other is the translation between the signal-to-noise ratio (Eb/No) and the resulting bit error rate (BER). The BER curves in STK represent theoretical performance curves. When modeling real demodulators, you may want to use an external modulation type with a slightly degraded BER curve. Typical systems run within 1-2 dB of the theoretical values at a given bit error rate. STK assumes perfect bit synchronization when demodulating the data to get a BER.

STK Modulators can be separated into five general categories: Common Analytical Modulators, Jammer/Interference Modulators, Coded Modulators, External File Modulators, and Script Plugin Modulators.

For more information on modulators, see one of the following categories:

Filter

To specify a filter model, select Use and browse to a filter model. For more information, see Filter Models.

Additional gains and losses

During communications analyses, it is often necessary to model gains and losses that affect performance but are not defined using built-in analytical models. STK enables you to model these by specifying miscellaneous gains and losses to add to the equation.

Post Transmit Gains/Losses. To define a Gain or Loss, click Add. Enter a brief description of the Gain or Loss in the Identifier field and its value in the Gain field. Remember to make it negative if you are entering a Loss. Once you enter the values, you can click Remove to delete an entry from the table. To change an existing entry, simply edit the fields in the grid. The value in the Pre-Receive field will reflect the net value of all gains and losses recorded in the table.