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6.1.3 The 'EXT' or External Position
The SMX100 serves as the voltage comparator and variable gain stage. It will enable the maintaining
of a constant RF voltage vs. frequency at the input to an imperfect load or a virtually constant E-Field
at a measurement point in space.
The front panel, ALC control, switches direct level control from the front panel Level Control
potentiometer to the output of a linear comparator. The comparator output level is dependent on the
reference input from the front panel Level Control and the input from the aforementioned detected
voltage or E-Field. The total gain of the leveling loop serves to maintain the output of the
comparator virtually constant and thus maintain the desired test level at the remote detector or remote
E-Field sensor.
The 'EXT' position enables the amplifier to automatically control an operator determined power level
by means of an external 0.0 to 5.0 VDC reference source connected to the External Source connector.
An example of a 0.0 to 5.0 VDC external input would be the output of a LDI or an EFS. Refer to
Paragraph 6.3 for procedures on leveling with an external voltage level.
6.2 LEVELING USING THE 'INT' MODE
When in the INT position, no outside controls are required. The only equipment required is a
frequency generator and the intended load. The procedure to use Internal ( 'INT' ) Leveling is
described below:
1) Turn the RF Level Potentiometer fully counter clockwise to Full Attenuation.
2) Set the ALC Switch to the 'INT' position.
3) Set the Signal Generator to the proper input drive level to obtain the desired power level.
Identify the desired testing parameters and determine the required input drive levels from the
Amplifier Data Sheets provided within Appendix A It is important to determine that sufficient
signal drive signal is generated to obtain and maintain the desired programmed power level. An
adequate load capable to operate within the power requirements should also be selected.
4) Adjust the RF Level Potentiometer until the desired Forward Power Level is displayed on the
front panel LCD display.
5) The amplifier is now ready to sweep a frequency range and automatically maintain the desired
power level with no further adjustments required. The power level will be maintained at the
operator set level and remain independent of changes to the input frequency or input signal level.
6) When sweeping the frequency range, best results are obtained at a sweep rate that is slower than
500 ms.
