Abstract: Starting from the basic functions to be implemented by the system, this paper introduces the overall design scheme and corresponding technical specifications. A detailed analysis is conducted on the functional characterization of the system's dynamic characteristics and the testing methods for these characteristics. Variable rate undersampling technology is used to address the problem of a wide sweep frequency range during data acquisition, and the dynamic characteristics of the A/D converter are tested. Keywords: Virtual instrument, frequency sweep measurement, frequency characteristics, DDS [b][align=center]The Design of Virtual Frequency Feature Scanning Device DouPeng[/align][/b] Abstract: From the point of view of basic functions, this paper briefly introduces the whole design scheme and related technical parameters. Mainly, the function expression for the dynamic peculiarity of a system and the ways to test the peculiarity are discussed. The system adopts shift under sampling technology to reduce the sampling rate during data acquisition. At the same time, the dynamic peculiarity of A/D is also tested. Keyword: VI frequency-scanning measure, frequency feature, DDS 1 Introduction With the increasing number of electronic test items and test scope, the gradual complexity of test objects, and the continuous improvement of test speed and measurement accuracy requirements, traditional test methods and test instruments can no longer meet the development needs. Traditional frequency characteristic testers mostly use LC circuits to construct sweep frequency oscillators, which are complex in structure, have single function, are inconvenient to operate, and have low cost performance. The emergence of virtual instruments has completely changed traditional instrumentation methods. Centered on a computer platform, it organically integrates computer hardware resources with certain external devices through software, fully utilizing the powerful computing, storage, and control capabilities of computers. This significantly reduces the cost and size of instrument hardware, shortens the development cycle, and enables various data processing functions such as acquisition, storage, and analysis through software. 2. System Overall Scheme Proposal The system design concept is as follows: During testing, the host computer first initiates a frequency sweep program, controlling the frequency sweep signal source to generate a sinusoidal signal with a frequency stepping according to a set value. Its amplitude is basically constant, and the maximum frequency variation range can reach 1-70MHz. After the signal passes through the network under test, its amplitude will change; that is, the distortion of the frequency sweep signal contains the network information of the network under test (amplitude modulation). Therefore, the envelope of this amplitude-modulated wave is the amplitude-frequency characteristic of the network under test. The amplitude-modulated signal is transmitted from the A/D section to the software processing module within the host computer, ultimately displaying the amplitude-frequency characteristics of the network under test on the front panel of the virtual frequency characteristic tester. The system block diagram is shown in Figure 1. From the overall system structure diagram, it can be seen that the system functions mainly consist of a control section, a data acquisition section, a frequency characteristic test and analysis/display section, and an expansion section. The control section can control the output frequency value of the sweep signal source in the system via a computer port, as well as control the sweep step of the sweep signal source. It can also control the sampling clock of the A/D acquisition board, i.e., control the sampling rate. The data acquisition section performs variable-rate sampling, adjustable arbitrarily from 8MHz to 65MHz, with a minimum step of less than 1Hz, and can automatically select the sampling rate based on the output of the sweep signal. The frequency characteristic test, analysis, and display section completes the test and analysis of the amplitude-frequency characteristics of the network under test and displays the test results. The functional expansion section mainly realizes remote control and the connection and management of the system with external I/O. For details, please click: Virtual Frequency Characteristic Tester System Design.