Research on the test method of the field universal automatic detection system for military shortwave radio stations

Radio whole machine testing is to measure the input and output of the radio and some key indicators and analyze the results to determine whether the radio is working normally. According to the actual application of military radio testing, especially under field conditions, it is very important to quickly and accurately detect the radio, and then judge the working status of the radio and replace the faulty module of the radio in time. This paper mainly studies the test method of the radio, including the test indicators, test connection relationship and test process of the radio.

1 System Introduction
The military shortwave radio universal detection equipment integrates equipment detection, fault diagnosis, and information query. It is developed on the basis of a hardware platform with the PXI bus system as the core and a software platform with Lab Windows/CVI as the core. The detection system consists of two parts: test hardware and test software. The test hardware platform consists of a PXI bus chassis, a radio frequency switch (PXI-2593), an audio analyzer (PXI-4461), a signal generator (PXI-5421), an oscilloscope (PXI-5112), a MIX card, and a computer. The test software mainly uses NI Labwindows/CVI7.1 as a development platform, combining the signal generator and the modulation and mediation software analysis package to simulate the input and output of radio frequency signals, and combining the oscilloscope and the spectrum software analysis package to calculate various detection parameters. The database uses MS SQLServer 2000 to save data, and uses MS Word 2003 to generate report documents. In the process of processing and calculating various eigenvalues, the following two data analysis and processing packages are mainly used:
(1) spectrum analysis toolkit;
(2) signal modulation and demodulation toolkit.
The principle block diagram of the military shortwave radio universal detection equipment system is shown in Figure 1.

The signal input and output interface on the object to be tested is connected to the testing equipment through an adapter, and the 220 V (50 Hz) AC power supply provides power to the testing equipment. The integrated power supply provides power to the object to be tested through the signal conditioning adapter unit, and the operator runs the software for testing and diagnosis. It has multiple functions such as functional testing, fault diagnosis, general measurement and maintenance data query; it can quickly isolate the faults of each single unit and combination to the replaceable unit; the detection coverage and diagnostic accuracy are ≥90%.

2 Test indicators and methods
There are many types of radios, and the performance indicators of different types of radios are also different. In the actual test environment, especially in field conditions, it is unrealistic and unnecessary to measure all performance indicators. In fact, it is only necessary to select the key indicators that can reflect the working status of the radio for testing, and then the working status of the radio can be judged according to the information obtained, and the faulty functional module can be replaced. Since most military radios are shortwave and ultra-shortwave radios, the test methods for the main performance indicators of these two types of radios are mainly studied. Now, taking the test of a certain type of shortwave radio as an example, the implementation of the test method is specifically explained.
2.1 Main test indicators
For shortwave radios, the test indicators that can be achieved by the automatic detection system are mainly: basic performance parameters of the transmitter, including RF output power, peak frequency, bandwidth, carrier suppression, etc.; transmitter audio response; receiver sensitivity; receiver intermediate frequency selectivity; receiver audio response; receiver audio output. The test item selection interface is shown in Figure 2.

2.2 Test method
2.2.1 Transmitter parameter test
Mainly includes transmitter basic performance parameter test and transmitter audio response test. The test block diagram is shown in Figure 3.

Connection method: Connect the radio's audio input port and the automatic test system's audio output with a wire, and connect the transmitter's output signal port and the automatic test system's oscilloscope port with a wire.
(1) Test of basic transmitter performance parameters
Mainly includes: RF output power, peak frequency, bandwidth, useless sideband suppression, carrier suppression, in-band secondary waves, and spurious narrowband RF components.
Test method:
① Spurious narrowband RF component test
Make the transmitter work without modulation, connect the transmitter output signal to the oscilloscope FXI-5114 input port, and the oscilloscope collects a set of data. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the value of the spurious narrowband RF component (in dB) can be calculated.
② Other parameter tests
Set the transmitter's working type, use the audio analyzer PXI-4461 to output the standard audio signal value to the transmitter, so that the transmitter outputs a modulated signal, and then use the oscilloscope PXI-5114 to collect a set of values. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the values ​​of characteristic quantities such as RF output power, peak point frequency, bandwidth, useless sideband suppression, carrier suppression, and in-band secondary waves can be calculated. [page]

(2) Transmitter audio response
Performance parameters of transmitter audio response test: Maximum change of transmitter audio response from 300 to 3 000 Hz, in dB. The index is required to be less than 4 dB.
Test method: Use the audio analyzer PXI-4461 to output the standard signal value to the transmitter, so that the transmitter outputs the modulated signal. At the beginning, the frequency of the standard signal value output by the audio analyzer PXI-4461 is 300 Hz. After the signal stabilizes, gradually increase its frequency value to 3 000 Hz. In the process of increasing the frequency, continuously use the oscilloscope PXI-5114 to collect data. Using the data collected by the oscilloscope PXI-5114, the processing function in the spectrum software analysis package is used to calculate the minimum audio response (dBm), maximum audio response (dBm), and maximum change value of the audio response (dBm) and other parameters.
2.2.2 Receiver index parameter test
The test indicators mainly include receiver sensitivity; receiver intermediate frequency selectivity; receiver audio response; receiver audio output. The test block diagram is shown in Figure 4.

(1) Receiver sensitivity
The main performance parameters that can be tested are: receiver sensitivity (in μV).
Test method: Generate a set of digital signals using related algorithms such as sine waves and square waves. Use the modulation function in the modulation and modulation software analysis package to modulate this set of digital signals into AM modulated RF signals, FM modulated RF signals or PM modulated RF signals as needed and output them to the receiver through a signal generator (PXI-5412). Then use an oscilloscope (PXI-5114) to collect a set of data. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the values ​​of characteristic quantities such as output power, signal-to-noise ratio and sensitivity can be calculated.
(2) Receiver intermediate frequency selectivity
Testable performance parameters: Receiver intermediate frequency selectivity. The performance requirement is 6 dB and the bandwidth is not greater than 4 kHz.
Test method:
① Mid-end detection. Specify the signal type, amplitude and frequency, use the signal generator (PXI-5412) to output the unmodulated RF signal to the receiver, and then use the oscilloscope (PXI-5114) to collect a set of data. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the signal frequency and gain value of the intermediate detection can be calculated.
② Low-end detection. First use the signal generator (PXI-5412) to output the unmodulated RF signal with the intermediate signal frequency to the receiver, and then gradually reduce the RF signal frequency until the low-end frequency gain is reduced to -6 dB, and then use the oscilloscope (PXI-5114) to collect a set of data. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the signal frequency and gain value of the low-end detection can be calculated.
③ High-end detection. First, use the signal generator (PXI-5412) to output an unmodulated RF signal with an intermediate signal frequency to the receiver, then gradually increase the RF signal frequency until the high-end frequency gain is reduced to -6 dB, and then use the oscilloscope (PXI-5114) to collect a set of data. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the signal frequency and gain value of its high-end detection can be calculated.
④ Test results
The difference between the high-end frequency and the low-end frequency of the test result value is the 6 dB bandwidth of the intermediate frequency selection.
(3) Receiver audio response
The testable performance parameters mainly include: the maximum change of the receiver's 300-3 000 Hz audio response. Unit: dB, required to be less than 4 dB.
Test method: Use related algorithms such as generating sine waves and square waves to generate a set of digital signals, and use the modulation function in the modulation and modulation software analysis package to modulate this set of digital signals into AM modulated RF signals, FM modulated RF signals or PM modulated RF signals as needed and output them to the receiver through the signal generator (PXI-5412). The frequency of the output modulated RF signal is set to 300 Hz at the beginning. After the RF signal output is stable, the frequency is gradually increased to 3,000 Hz. During this process, an oscilloscope (PXI-5114) is used to collect a set of data. This set of data, combined with the relevant processing functions in the spectrum software analysis package, can be used to calculate the values ​​of the characteristic quantities such as the minimum audio response (dBm), the maximum audio response (dBm), and the maximum change in audio response (dB).
(4) Receiver audio output
The main performance parameters that can be tested are: receiver rated audio output, receiver maximum audio output.
Test method:
① Use related algorithms such as sine wave and square wave to generate a set of digital signals. Use the modulation function in the modulation and modulation software analysis package to modulate this set of digital signals into AM modulated RF signals, FM modulated RF signals, or PM modulated RF signals as needed and output them to the receiver through a signal generator (PXI-5412).
②When testing the rated audio output (mW) of the receiver, select the signal amplitude of 5 V. After the signal output is stable, use the oscilloscope (PXI-5114) to collect a set of data. Using this set of data, combined with the relevant processing functions in the spectrum software analysis package, the value of the rated audio output of the receiver can be calculated.
③When testing the maximum audio output of the receiver, adjust the amplitude of the RF signal to 7 V. After the output is stable, use the oscilloscope (PXI-5114) to continuously collect data. Then gradually increase the output amplitude. When the maximum output is observed, complete the test. Use the data collected by the oscilloscope and the relevant processing functions in the spectrum software analysis package to calculate the value of the maximum audio output of the receiver.

3 Conclusion
The test indicators and test methods of the general automatic detection system for military shortwave radio stations are introduced through the test implementation of specific test parameters of a certain type of radio station. There are many types of radio stations, and the test methods are not exactly the same. In addition, the test interfaces and test parameters of each radio station are different, but the test principles are generally the same. For measuring transmitter indicators, a modulated signal is required to modulate the carrier. The modulated signal is transmitted through the radio station and sent to the measurement module to measure the transmitter indicators. For receiver indicator measurement, the RF signal reaches the radio receiver and is demodulated to obtain an audio signal. The audio signal is sent to the measurement module through the audio port to measure the receiver indicators. Understanding the test methods and processes of various types of radio indicators is the basis for system test implementation.