A scan generator creates a sawtooth waveform to change the output of a signal generator, allowing a test setup to measure the response of devices within a range of frequencies. Sweep generators are used to test frequency response over a range of frequencies. The frequency range of a device can be evaluated by a sweep generator and spectrum analyzer. The power amplifier is said to have a frequency range of 148-152 MHz.
A scan generator is an electronic test generator that creates a periodic sawtooth waveform intended to change the output of a second signal generator, which is usually a radio frequency (RF) generator. The periodic sawtooth waveform rises to a peak level, then rapidly drops to a low level, then repeats the process. A sweep generator output can be used to control the frequency output of a signal generator to generate a sweep frequency output. In general, a sweep generator allows a test setup to measure the response of devices within a range of frequencies or frequency range almost simultaneously.
Sweep generators are used to test frequency response over a range of frequencies. Whenever RF circuits or electrical circuits have a specific frequency response, the scan generators can generate the test signal which will cover the specific frequency range. The basic sine wave or sine wave is a periodically varying voltage with time that flows smoothly from zero to a positive peak, then to zero, then to a negative peak, and back to zero. A complete cycle will have two zero points and two peak points, which are positive and negative.
The frequency domain description is used when the tested device has to operate on a certain frequency range. The frequency range of a device can be evaluated by a sweep generator and spectrum analyzer, the corresponding test equipment. This has a two dimensional screen which shows both vertical power levels and a horizontal frequency reading. When monitoring a signal with the spectrum analyzer, the vertical axis is still the amplitude, in watts (W), but the horizontal axis is the frequency, in hertz (Hz) instead of time units.
In an amplifier with transistor, inductor, and capacitor circuits, net gain or amplification is expected over a range of frequencies. For an RF power amplifier, gain is observed by measuring the input to the amplifier. If the output is 1W while the input is 0.01W, there is a gain of 100. Since the center frequency is actually 150 megahertz (MHz), a normal next parameter involved is bandwidth, which is the range of frequencies below and above center where the gain is half the gain at the center frequency. This is also referred to as “–3dB” points, where –3dB refers to half the power gain.
If the lower -3dB point is 148 MHz and the upper -3dB point is 152 MHz, the power amplifier is said to have a frequency range of 148-152 MHz. The sweep generator can then be set so that the its lowest frequency is 148 MHz. The upper level of the scan generator causes 152 MHz to be output from the signal generator. If the sawtooth generator within the scan generator is turned off, the signal generator output will stop scanning in the 148–152 MHz range. Without the scan generator, the signal generator output will be at a fixed frequency of about 150 MHz.
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