"From the" Electronic News ", there is an introduction to the secondary frequency band receiving head for the main components with the high frequency head of ordinary TV. It is possible to see the article introduction. The components are intact, the component weld Formula, high frequency head is installed in vertical installation, tunes 100K potentiometers with a self-bandped frequency switch. So no to attach power and speaker test machines, and discover 1K in the original picture The fine-tuning potentiometer is not installed in the component. The position of one LED is reserved in the lower left of the board. The analysis is a tuning indicator. After the soldering is on one LED, it is found that there is a certain impact on the received signal, and remove it. A 15V switching power component is a power supply, and it is found that the interference is very large. It is also found that this component cannot use the switching power supply. Take the power input of one of the sets of direct input components using a hand of about 30 watts of power. : Access to a speaker audition, the overall sensing frequency adjustment is not very fine; the reason is that the handle of the tuning potentiometer is too thin, it feels a lot after using the handle on an old radio. It also found it in the adjustment. Many questions: If the power supply stabilization set is large, the heat is large, in order to ensure that the component works properly, a heat sink is installed, and the heat sink is only slightly hot.
The component work is basically normal, but for the component to find a suitable outer casing, it is also a brain. I have found a suitable thing. I didn't find a suitable. I didn't lose it. I used it! Pack the transformer! In the box, the components simply use the screw to be fixed outside the box, and the switch and power indicator. The speaker is mounted directly on the housing. In order to strengthen heat dissipation, the speaker uses a small fan on a computer CPU from the side direct blowing circuit board. The power supply is supplied from another set of winding strings of the transformer. And install a Q9 socket on the housing, you can directly install 1.2 m Rod antenna or the eight wooden antenna described above.
Finally completed appearance
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Overall evaluation: The frequency reception range and article introduction of the receiving head are basically consistent, that is, for the frequency modulated radio (88-108MHz), there is no adjustment. Frequency adjustment is not very convenient; no frequency indicator, use the article introduction with the article Head and instructs the current frequency on the circuit, it is found to have a certain interference. The individual components have a large amount of heat, it is recommended to install the heat dissipation device. It is better than my eight-timber antenna, and the antenna when receiving the 900m simulation of the mobile phone. The length is critical to receiving. The frequency stability of the components can be, and this component has certain practical significance as the principle of learning the audio audio receiving part or debugging the transmitting circuit.
(2) I use 45 ~ 925MHz secondary frequency frequency frequency receiving head
(Xiao)
Summer, a FM enthusiasts send me a full-frequency receiver component, maybe he doesn't know how to install it. Just a similar article (below), after several considerations, it is confirmed to be this product. After installing, the effect is of course good, just the frequency indication, the received frequency is only speculated, at 144--148MHz, 220-225MHz, 430--440MHz, 902-925MHz amateur frequency band unable to play, the frequency band is too wide. Second, I suggest that fans use the battery to power, try to play your own advantage to the development of this product, I think it is very valuable, just my time is limited. I wish you can develop new features!
The following is a description of this product:
The commercially available radio can generally only receive 88 to 108 MHz frequency modulated broadcast, the frequency band is narrow, and the sensitivity is low. The receiving heads described herein can receive a frequency modulated signal in the range of 45 to 925 MHz, which can be used to listen to broadcast, television sound, monitor cordless phones, walkie-talkies, etc., have a wide range of applications, and have a practicality and interest. Its circuit is integrated according to the communication receiver and radio circuit, with high sensitivity (1μV), high stability, etc., especially suitable for remote reception. First, the principle of the circuit uses 1 high frequency head, 4 integrated circuits, constitutes a typical secondary frequency conversion superheterodyne receiving head. The first intermediate frequency can be selected between 31.5 to 38 MHz, the unit is selected from 315 MHz, and the second medium is 107MHz. The audio output is about 02W, the static current is 100mA, and the circuit is shown in the drawings. After the radio signal is high, the output 315MHz first intermediate frequency signal is sent to IC1, and the second hidden frequency signal of 422 MHz is mixed with 422MHz, which is generated by a second hive frequency signal of 107 MHz. The signal is sent to IC2 through a 107 MHz triple filter. IC2 has functions such as medium release, audio demodulation, tuning instructions. The demodulated audio signal is enlarged by IC3 to drive 8Ω / 05W speakers or headphones. The voltage controls the high frequency head AFC terminals in the IC2 identification frequency output terminal, which can achieve the purpose of automatic frequency fine-tuning. The power supply is provided with a DC-DC converter composed of 7805, 7812 regulated integrated circuits and peripheral components, providing 5V, 12V, and 30V operating voltages to each portion of the circuit. 7812 The voltage difference is required for 3V, so the input DC voltage should be above 15V.
Second, the element selection 1 High frequency head should be used to select a full-intensive channel high frequency header, and use the sweep meter, the oscilloscope and frequency calculation to modify the high frequency head, and will ensure that the overall performance is constant, The U-band frequency is increased to 960 MHz, and the frequency limit in the actual use is 925MHz. The measured frequency range is from 45 to 155 MHz, H-section 150 ~ 465MHz, and the U section 440 to 960 MHz. 2 Second Improved / Mixed Select High Performance Communication Dedicated Circuit NE602. The integrated circuit uses a double balance mixer, has a good signal-to-noise ratio and three-stage intermodulation indicators. In the case where there is no external high place, the receiver has a sensitivity of 02μV, and thus it can save the first medium. Put, simplify the circuit. 3 The second middle placement, audio solution is used to use the FM / AM radio integrated circuit LA1260 of the high signal-to-noise ratio. The integrated circuit contains two parts of AM / FM, this unit is part of its FM portion, the AM part is vacant, the LA1260 has a high signal-to-noise ratio, the FM portion is 81dB, the common integrated circuit (CXA1019, CXA1238, TTA8127) is 11dB, The advantages of small distortion, strong anti-interference ability. The 430V DC-DC converter selects the NE555 dual-time base circuit, and the NE555 is composed of a self-excited multi-excitation oscillator with the peripheral components, and the 400 kHz square wave is output to the multiplier rectifier circuit. When the input voltage is 12V, the output voltage is 315V. 5 Tuning Components use 100KΩ potentiometers of the own band switch for frequency coarse adjustment, 1KΩ single-link potentiometer for frequency fine-tuning. The tuning component has no frequency indication, and one 30V DC voltage header is used and between the high frequency head VT terminal and the ground, and the reception frequency is generally understood based on the indication voltage. The frequency band switching order L-H-U, the frequency increases at the time of clock-tuning, and the reverse clock is reduced. 6 High Frequency Transformer B1, oscillating coil B2 uses the molded television medium TRF1445, the original resonant frequency 38MHz, B1 does not need to be revoked, and the resonant capacitor can be increased, B2 is removed from 1 lap, and the resonant frequency is about 415 MHz. 7 Antenna is a key component of this unit, and there is a standardized antenna according to the reception frequency band, or the 15 m Rod antenna can be used, and the optimum length of the antenna is 15 ~ 30 cm according to the actual situation. Selection. The antenna is connected to the high frequency head with a crude single copper wire, and the connection length is not more than 3 cm. Third, the debugging and use of this machine except for high frequency heads, only one tuning point, that is, the second vibration frequency adjustment, the frequency is required to be adjusted, no frequency timing, only the modified B2 magnetic core The outer (inverse time) is rotated in a 1/3 circle, and the resonant frequency is approximately 422 MHz. This machine uses more simple and tuning, put the fine tuning potentiometer in the middle position, then slowly turn the tuning potentiometer, receive the signal, then adjust the potentiometer, make the sound quality.
(3) 45-925MHz FM stereo receiving head
(1) "The circuit introduced in" FM receiving head "" has many shortcomings in the design. The following receiving heads are summarized, improved, and the receiving head has a large increase in performance. First, the problem of the original collar is 1, the selectivity is poor. The second local oscillator / mixing circuit (NE602) uses a simple single tuning loop, and thus selectively, the passband characteristics are poor, resulting in a mixing head in the receiving head, and the phenomenon of strong stages. To resolve this issue, you must add a dual tuning loop before the NE602, and the band width is reduced to about 1 MHz. 2, low sensitivity. Although NE602 has a high input sensitivity indicator, the effect is not obvious in actual use, mainly reason is that the medium frequency signal voltage of the high frequency head is low when receiving the weak signal, causing the mixing efficiency of the NE602 to decrease, mixed gain Reduce. Thus, it is necessary to add a level between the high frequency head and the NE602. 3, tuning accuracy difference. Although the tuning component of the receiving head tuning is used in a precision 30-circle potentiometer, the actual tuning accuracy is still low due to too wide reception frequency (3 15 MHz per turn). It can be used to increase the tuning accuracy by 36 times by resistivity, switch conversion. 4, signal to noise ratio. To simplify the power supply, it is convenient to use a DC power source, and the receiving head tuning voltage is provided by a high frequency DC-DC converter. Due to the single-sided panel, the high-frequency radiation interference generated by the converter is very obvious. To this end, the double-sided large-area pore printed plate must be used, and the large area is used to screen it. The experiment has proved that the effect is excellent, and the noise of interference is reduced to the extent of unscrupulous, and the signal-to-noise ratio has improved. Second, the new receiving head 1, the circuit consists. Receive head from a high-frequency tuner, first medium placement, second local oscillator / mixer, second medium, FM demodulation, stereo decoding, automatic gain control, tuning component, power amplifier, 30V boost circuit, regulator circuit Equisical. 1. The high-frequency tuner is the most important component of the receiver. Although the high-frequency tuner dedicated to the communication machine is good, the price is quite high, and it is impossible to buy from the market. Therefore, the high-frequency tuner has to use the TV. Supplement high frequency head. The circuit structure and communication machine high-frequency tuner of the full increase of high frequency heads have no significant difference, as long as it is not a special requirement, it is feasible to choose a TV. The total variety of high frequency heads is much variety, the circuit is different, the sensitivity of the discrete element class is low, and it is not available. It should be selected as the high frequency header of the TDA5300T series. "" Chengdu Xu Guang "" TDQ-3B6 high frequency head as an example, the high frequency head is highly placed by three sets of independent LC input loops, double gate field effects, and the dual tuning loop and TDA5330t. The three-band circuit is independent and does not affect each other. The frequency covers 45--900MHz, especially convenient to modify. The high frequency head is more simple, the input loop, the vibration does not adjust, the adjustment focus is the dual tuning loop, so that the original 8MHz intermediate band width is compressed to 1 MHz below to improve the selective indicator. Conditional available sweepers are adjusted, and it can also be used directly when there is no instrument, but the sensitivity is slightly poor. 2, 38 MHz first intermediate frequency filter consists of B1, B2, C3, C4, C5, B1, B2 select the exemption, the size of the C4 capacity determine the intermediate frequency bandwidth. The filter center frequency is 38MHz, with a bandwidth of 600 kHz. 3, the first middle, the second local oscillator / mixing circuit consists of TA7358AP, and TA7358AP has been used in the FM radio, the high amplifier gain 23dB, the mixing gain 31dB, and the local imitation stability is quite good. The circuit configuration of this stage is basically the same as the frequency frequency radio tightener, except that the operating frequency is different. B3, B4, and B5 are all used for swing, and this level does not need to be debugged. 4, the second pre-primary release is composed of T1 and the relevant components, and the gain is 20 dB. 5, the second middle placement, FM demodulation, stereo decoding circuit and "Electronic News" This year, "High-fidelity Virtus Stereo Tunume" "is the same, and the stereo decoding circuit is changed from LA3370 to LA3430. The voltage controlled oscillator of the LA3430 uses a 456 kHz ceramic magnetoscope to improve stability and reduce distortion. The high-frequency head AGC control circuit has been added to prevent strong signals from blocking. In order to further improve the stereo separation, the stereo output filter is changed from the RC dual T filter to the LC filter, and the stereo separation is up to 50 dB. 6, the AGC control circuit consists of T2 and the relevant components, and the IC2 6 foot output voltage varies between the strength of the input signal, but the voltage cannot be directly used for reverse AGC high frequency head, must be inverted After the AGC control can be used. 7, 30V DC-DC converter provides high frequency head tuning voltages, input voltage 12V, output voltage 30V. Using a boost circuit instead of the power transformer tuning voltage winding, the power supply circuit is simplified, and the direct current can be used. 8, the tuning component is constructed by the tuning potentiometer, the frequency band switch, the channel switch, the tuning potentiometer selected 30-turn precision potentiometer, and the frequency segment switch is combined on the tuning potentiometer, and the role of R1 R4 is the three bands of L, H, and U A section is divided into high, medium and low, and the tuning accuracy is three times higher through a 3 × 3 switching conversion. ⑨, amplifier consists of LM386, which is only used for communication signal listening, and it is preferred when listening to stereo programs is an external active speaker. 2, the quality of the antenna antenna is directly related to the quality of listening, and sensitivity and other indicators. In the case of low requirements, the 1.5 m Rod antenna can be used to listen to local FM radio and communication signals. If you want to receive a remote signal, you must use an outdoor antenna. Listen to the remote frequency frequency broadcast, it is best to use the outdoor antenna dedicated to the frequency band broadcast band. If you want to use the communication signal, the full-band TV antenna can also be used, but it is worse than the dedicated channel antenna. 3. The quality of power supply is also closely related to the overall sensitivity, and the signal-to-noise ratio has a close relationship. Transformers, rectifiers, pre-regusal stabilization should be away from the receiving head to avoid interference. The transformer should use 25W high-quality products. When the receiving head regulator circuit, the power consumption of the adjustable pre-pressure circuit can reduce the power consumption of the receiving head, reduce the heat of the receiving head regulator circuit, and improve the stability of the receiving head. . The regulator circuit uses low-power, low pressure difference regulator integrated circuit, the lowest input voltage 12.3V, the optimal input voltage 12.6V, and the highest input voltage 15V. 4, main performance indicator sensitivity ≥ 0.5UV selective ≥75dB stereo separation ≥ 50dB static current ≤100mA "
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