01. What is the principle of the IF receiving part? One IF? What is the second intermediate frequency? Adopting secondary frequency conversion superheterodyne method, the first intermediate frequency is 49.95MHZ and the second intermediate frequency is 450KHZ.
02. What is the MPF tuning principle of RF reception? How to tune? effect?
03. What is the principle of APC circuit and how to implement it? How to achieve high and low power when it occurs? The automatic power control (APC) circuit stabilizes the transmitted output power by detecting the drain current of the final amplifier field effect transistor Q519. The voltage comparison circuit U513 uses the set reference voltage to compare the voltage obtained from the final stage current. The automatic power control voltage is proportional to the difference between the automatic detection voltage output by U513 and the reference voltage. This output voltage controls the FET power amplifier to keep the output power of the transmitter part constant. The output power of the transmitting part can be adjusted by controlling the APC voltage through the microprocessor.
04. How to realize the wide and narrow bandwidth of IF? Why should we implement wide and narrowband? Implemented through surface acoustic wave filters to adapt to different channel spacing requirements. Including 25k, 20k, 12.5k.
05. What is the role of TA31136? What is its input signal? How many signals can it output? What's the use? What is the relationship between output and input? It is the second intermediate frequency detector, which converts the 49.95MHZ signal output from the first intermediate frequency into a 50.4MHZ audio signal output; the input is the second intermediate frequency signal; the output signals include: inverted amplification output, demodulated AF signal output , IF amplified signal output,
06. How to implement the squelch detection circuit? How does the MCU detect this signal? How does it correspond to the signal-to-noise ratio? Squelch circuit: An electronic circuit that cuts off a wireless receiver when the signal is too weak and only noise is received. When the walkie-talkie performs IF demodulation on the received signal, the sub-audio signal is filtered, shaped, and input into the MCU. It is compared with the CTCSS frequency set by the unit, and then a level control AF MUTE and SP MUTE is generated to determine whether Turn on mute. The MCU detects this signal: part of the audio signal output from the mid-frequency processing circuit TA31136 enters the FM integrated circuit again, rectifies its noise component through the filter and amplifier, and generates a DC voltage corresponding to the noise component. Sent to the analog port of the MCU for detection. The input DC voltage is compared with a preset voltage value, and the output of the speaker is controlled to be turned on or off based on the comparison result.
07. How to implement the RSSI detection circuit? How does the MCU detect this signal? What is the corresponding relationship between RSSI and reception level? The RSSI terminal of TA31136 outputs a DC level for the IF amplifier according to the input signal level.
08. How are the pre-emphasis and de-emphasis circuits composed? What role does it play? What are the technical indicators? Composition: It is mainly realized by the pre-emphasis and de-emphasis circuits in the AK2346. The peripheral circuits can also realize the pre-emphasis and de-emphasis functions. The pre-emphasis is realized by the high-pass filter, and the de-emphasis is realized by the low-pass filter. Function: The sound quality mainly depends on the technical indicators of the pre-emphasis and de-emphasis circuits
09. How are the compression and expansion circuits composed? What role does it play? What are the technical indicators? Composition: Composed of the compression and expansion circuit in AK2346. Function: The application of voice processing circuit, voice companding circuit and low-level expansion circuit, which has a good effect on fidelity of speech.
10. How are two-tone, five-tone, sub-tone, sub-tone digital, and dual-tone multi-frequency signaling composed? What does it do? How is it generated and decoded in TC900? How was it prepared? Answer: Two-tone signaling consists of two audio signals, A Tone + B Tone. First send A Tone for a period of time, then after a period of time, send B Tone. You can choose to call the corresponding intercom using 2-TONE signaling; 5-tone signaling has the same function as two-tone signaling, but the difference is that it is composed of five frequencies; CTCSS (Continuous Tone Controlled Squelch System), a continuous tone controlled squelch system, Commonly known as sub-audio, it is a technology that adds frequencies lower than the audio frequency (67Hz-250.3Hz) to the audio signal and transmits it together. Because its frequency range is below standard audio, it is called sub-audio. When the walkie-talkie performs IF demodulation on the received signal, the sub-audio signal is filtered, shaped, and input into the CPU. It is compared with the CTCSS frequency set by the unit to determine whether to turn on mute; CDCSS (Continuous Digital Controlled Squelch System), The continuous digital control squelch system has the same function as CTCSS. The difference is that it uses digital encoding as the condition for whether to turn on the mute. Using the CTCSS/CDCSS function can avoid receiving irrelevant calls. DTMF (Dual Tone Multi Frequency), dual tone multi-frequency, consists of a high frequency group and a low frequency group. The high and low frequency groups each contain 4 frequencies. A high-frequency signal and a low-frequency signal are superimposed to form a combined signal, which represents a number.
DTMF signaling has 16 codes. Two-tone/DTMF signaling can be used to selectively call the corresponding intercom.
11. Will turning on PA have any impact? How to reduce this impact?
12. What functions does AK2346 have? How to encode and decode MSK signaling? What is the optimal input level for MSK decoding? How do I adjust this input level? What effect does the signal-to-noise ratio of the input signal have on the bit error rate? The functions of AK2346 include: audio processing; sending and receiving amplification; scrambling; pre-emphasis and de-emphasis; MSK encoding and decoding, limiting function; audio compression and amplification, etc. After the external analog sinusoidal signal comes in, encode and decode by setting the control register, 1control register 2 and volume register 2 of the AK2346. At the end of decoding and encoding, the AK2346 will generate an interrupt signal to notify the MCU to store the data, and then the MCU will interleave and reverse the data. The conversion algorithm is used for calculation. Minimum frequency shift keying pursues the continuity of the signal phase path and is a type of binary continuous phase FSK (CPFSK). This modulation method can obtain orthogonal modulation signals with a minimum modulation index h=0.5.
13. What is the working principle of the chip? How to solve the data conflict problem between it and AT24C256's SDL and SCL? What is the relationship between RTC-INT and MCU? CHARGEHow to charge the clock battery? Since the CPU shares the I2C bus of the CPU, some resource conflicts will occur, which are solved by the mutual exclusion signal management of the OS system. In addition, they are solved by the CPU time-sharing operation. When R5VC387 is issued, the MCU Sending its startup address does not allow the AT24C256 to operate the data line during this time.