Production of small power TV transmitter, TV Transmitters
Keywords: TV transmitter circuit diagram
Author: Lin De Yao Huang Yingming
I. Introduction to the principle of circuit
The modulation chip uses μPC1507 or TA7673AP integrated circuit, and μPC1507 is a modulator set circuit produced by Japan NEC, and TA7673AP is the RF modulation integrated circuit produced by Toshiba, Japan. The external pins and internal functions are exactly the same, both of them. Use. The audio signal is input by the socket CK1, and after adjusting the potentiometer RP1 to a suitable voltage, the capacitance C5 is coupled to the sixth pin of the μPCI 507 to make the buffer amplifier, the resistor R2, and the capacitor C1 constitute an audio troneum precharge circuit to improve the audio signal. The signal-to-noise ratio of the high sound segment is resonant to 65MHz, and the integrated block is 6.5MHz in the integrated block and the image carrier signal is mixed, generating the carrier frequency FS of the frequency modulated signal than the image carrier frequency FO high 6.5 MHz. TV support signal output from the integrated block 2 foot. The image signal is input from the socket CK2, and after adjusting the potentiometer RP2 to a suitable voltage, the calibration of the image signal is coupled to the plug of the image signal by the capacitor C8 to the white level limit, and the built-in subcarrier is oscillated. The device or an external image carrier signal realizes amplitude modulation, and the television image signal outputs from the integrated block 15 foot, and after mixing with the sound signal, the television signal (image signal is transmitted) The fo is modulated, and the audio signal is frequency modulated as FS). The power amplifier is shown in the figure below, the triode VT1 is a buffer amplifier and a t-tuning loop resonant frequency is (fd + fo) / 2 (MHz), with a bandwidth of 8MHz, allowing the channel signal of this channel to pass, the remaining signal The purpose of being suppressed and reached with bandpass filtering. Three-pole VT2, VT3, VT4 constitutes a large-scale tuning, and the output power is greater than 120 mW. The TV signal is output from the socket CK3 output to the antenna to emit out.
Second, print board design skills
Frequency electronic circuitry is in the correct case of the schematic, the key is to make the result or not, the key is how to carry out the board, because the high-frequency circuit contains very rich variety of harmonic components, these harmonic ingredients with the circuit board Walking around, interferes with normal signals, so you have to take this signal through the board, eliminate it in the germination state. The following principles must be followed when the board: (1) The layout of components should be reasonable, and the small signal components are pushed forward, and the final level is in the end; if the above layout is met, it is necessary to consider it as much as possible. Whole clean, such a product has a sense of grade. (2) Part of the printed board, the power supply line design skill is the first stop of the power supply, the first station is the final (large current), the second stop is in the middle, the third station (front level) It is a small current, so that the farthest is to eliminate the interference ingredients such as the signal input stage, the station and the station. (3) Partial circuit negative (ground) of the printed board, the printed board is taken to further eliminate the source of random fluctuations in a large-area coated method; in the stage and the level should be wrapped up with a metal leather package to shield , Introduce the radiation source through the air to the ground.
Third, component selection and homemade
1. The homemade component oscillation coil L2 uses φ0.4 to 0.5 mm enamel wire, and the water brush core (φ is 5 mm) wraps a 5-circle, as shown in the following figure (a); the coupling coil T2 ~ T5 is the two groups The coil is tightly coupled together, as shown in the following figure (d), the outer and secondary coil outer diameters are the same as the oscillation coil, but the primary coil is around 2 laps. To lead the tap, the arrow of the secondary coil is shown in Fig. (B), (c), respectively, respectively.
2. The representation of the components in the components is shown in the following table.
Serial number
Device name
Specification model
Schematic number
quantity
1
Porcelain capacitor
CC1-160V-3.3P
C37
1
2
Porcelain capacitor
CC1-160V-47P
C36
1
3
Porcelain capacitor
CC1-160V82P
C4
1
4
Porcelain capacitor
CC1-160V-10P
C29, C24, C16
3
5
Porcelain capacitor
CC1-160V0.01
C18, C31, C39, C30, C17, C7, C33, C38
8
6
Porcelain capacitor
CC1-160V-0.1μ
C3
1
Seduce
Porcelain capacitor
CC1-160V-150P
C21
1
8
Porcelain capacitor
CC1-160V-100P
C23, C13, C26, C15, C28
5
9
Porcelain capacitor
CC1-160V-47P
C12
1
10
Porcelain capacitor
CC1-160V-51P
C6, C5
2
11
Porcelain capacitor
CC1-160V-
C10, C1, C11, C9
4
12
Electrolytic capacitor
CD11-16V-1μ
C2C8
1
Mean
Electrolytic capacitor
CD11-16V-470μ
C38
1
14
Semi-variable capacitor
CTC-3-10P
C20, C32, C25, C14, C34, C35
6
15
Resistor
RT14-10
R30, R20, R22
3
L6
Resistor
RT14-22
R13
1
In one
Resistor
RT14-47
R9, R17
2
In
Resistor
RT14-120
R12
1
19
Resistor
RT14-220
R23
1
20
Resistor
RT14-330
R4, R8
2
twenty one
Resistor
RT14-470
R14, R3, R18
3
twenty two
Resistor
RT14-680
R26
1
twenty three
Resistor
RT14-1K
R16, R27, R7
3
twenty four
Resistor
RT14-2.4K
R11
1
25
Resistor
RT14-2.2k
R25
1
26
Resistor
RT14-3K
R5
1
27
Resistor
RT14-7.5K
R6, R19, R15
3
Twist
Resistor
RT14-8.2K
R21
1
29
Resistor
RT14-12K
R4
1
30
Resistor
RT14-10K
R10
1
31
Resistor
RT14-15K
R24
1
32
Resistor
RT14-22K
R1
1
33
Resistor
RT14-56K
R2
1
34
Potentiometer
WH124-4-1K
Rp2
1
35
Potentiometer
WH124-4-100K
Rp1
1
36
inductance
10UH
L1
1
37
Triode
BFR91 or 9018
VT1, VT5, VT3, VT2
4
38
Triode
2SC3355
VT4
1
39
diode
2EFL01A
D5
1
40
diode
D1 ~ D4
IN4002
4
41
Integrated block
LM7812
IC3
1
42
Integrated block
LM7806
IC1
1
43
Integrated block
TA7673AP or UPC1507
IC2
1
44
Medium week
T6.5MHz TV in the week
T1
1
45
Homemade inductance
Be
T2-T5. L2
5
Be
Fourth, debugging skills
1. The static work point debug static time measurement The voltage of each pin of the integrated block The voltage of each pin of the triode should meet the above table, the voltage value shown in the table below, deviates from the above table, and the value should be adjusted when the above table is adjusted.
UPC1507 / TA7673AP Integrated Circuit Values
Pin
1
2
3
4
5
6
Seduce
8
9
10
11
12
Mean
14
15
16
Voltage (V)
0
3.9
2
4.8
4.8
2.6
0
5.9
Mean
twenty three
40
1.9
3.3
0
4
3.2
Be
Three-pole principle map
UB (V)
UE (v)
UC (V)
Vbe (v)
VT1
3.73
3.03
9.10
0.7
VT2
"
1.24
11.2
0.72
VT3
1.5
0.7
11.70
0.74
VT4
1.01
0.21
12
0.75
VT5
4.45
3.70
10.8
0 70
If the triode VT2 design value Ic is 10 mA, it is found that the emitter voltage is 1.22 V in the measured process, then the emitter current is 101mA, IC≈EE, basically meet the design requirements. If the circuit component parameters are different, if the triode B value is different, the IC is large or less, that is, the UE value is large or less, and the bias resistor R10 on the triode VT2 can be changed or small, and the rest is similar. Adjust the relevant components to meet the requirements.
2. After the emitting antenna, the emitting antenna will be installed when installing: First, it is necessary to match the transmitter output impedance, and the omelet of the eight-timber antenna should be connected according to the pattern shown in Fig. (A) to connect to it can be implemented. The antenna and the 75 feed line, the feeder and the transmitter impedance matching, the other end of the feeder can be connected directly to the RF output port of the unit; after the antenna is set, it should pay attention to the leader to align the receiving area, as shown below (b) Show, the emission distance is greater than 2.5 km. Second, if the antenna is set to the roof, it is necessary to install the lightning device.
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