Production and debugging of crystal frequency modulation transmitter

In various radio production projects, FM transmitters have always been favored by many enthusiasts. However, the production of this aspect involves some high-frequency technology, which has caused many beginners in production and debugging to be stopped by vibration, interference, running frequency, A series of faults such as distortion are distracting and even give up. This article takes the "FT3S FM Transmitter Kit Circuit at hand as an example to introduce readers to the FM transmitter installation experience and common troubleshooting methods in detail, I hope to help readers a little.
The simple wireless microphone is a typical of wireless transmitters, although it has won the favor of many readers with its "ready to install" advantage. However in the circuit. The severe frequency drift caused will be unbearable to us. The crystal oscillator used in the circuit of Figure 1 effectively avoids the fatal weakness of "running frequency"; the frequency multiplier sets the operating frequency to the frequency band that can be received by ordinary radios; and the multi-stage high-frequency amplifier raises the RF power to 80mW. To achieve a longer distance launch.

Selection of components: see Figure 1 for model parameters of all components; 1. Miniature color-coded high-frequency capacitors are the first choice, and horizontal installation is used to reduce the influence of lead inductance; 2. JT selects an overtone crystal with a nominal frequency of 49.860MHz. For different output power requirements, other frequency points can be selected according to the actual situation; 3. L1, L2, L3 are frequency-doubling and high-frequency amplifier resonant inductors, it is recommended to use Î¦0.8mm silver-plated wire wound on 4.0mm skeleton, the number of turns is 5T, 4T, 5T; Vl, V2 determine the high frequency For noise figure and gain, low-noise tubes with Î² value around 300 can be selected, such as C945, C9014, etc .; V3-V5 requires Î²100-120, fT> 500MHz, C1975, C9018, etc. can be used. V6 requires Î² = 100, fT> 800MHz, and Pc> 500mW high-frequency medium power tubes, such as C2581, D40, and C2053. When the output power is not high, it can be omitted. TX can use whip antenna or 1.5m flexible wire. When the operating frequency is 100MHz, the length of 75cm is the ideal value.
Production and commissioning: all components should be collected before making, and the quality and parameters should be carefully tested, and then a suitable circuit board should be designed according to the required volume. All in all, good component quality and proper printed board layout are the guarantees to effectively improve the self-made power. The main debugging steps are as follows:
1. Weld all components together with the antenna on the printed board. The requirements for the installation and welding process are: shorten the component leads of the high-frequency part as much as possible; install the resistors and capacitors horizontally as much as possible, and there is no virtual soldering or de-soldering.

2. Refer to Figure 2 for temporary lap welding of a simple field strength meter for debugging.
3. Power on the transmitter with a voltage of 9V. The field strength meter lead is 5cm away from the antenna, and the distance between turns L1, L2, L3 is repeatedly adjusted to maximize the field strength meter reading, and the resonance capacitance of each stage is adjusted if necessary.
4. By modifying the antenna length within a small range, the field strength indicator will continue to increase, and pay attention to the adjustment, the transmitting antenna should avoid contact with the human body or metal.
5. Finally, put the circuit into the metal shield to fix it, and connect the ground wire to the shell.
The above debugging process seems to be relatively simple, but not every reader can complete it smoothly, and will encounter some problems more or less. Here are some problems and solutions that often occur in actual production:

1. When used at close range, especially when picking up signals with high intensity, the radio has severe howling or distortion. This is due to the high gain of the audio amplifier stage and the high electrification sensitivity of the electret microphone. The solution is simple: just increase the resistance of R3 to 820Î©.
2. When using the AIN interface to input the sound source signal, the radio output sound is small and accompanied by hum. I believe that many of these friends have experienced this kind of problem in the past. One of the reasons: it is caused by the use of a rectified power supply with poor filtering effect, but if the battery power supply is still not used, it may be because the high-frequency signal is too strong and interferes with the amplifier circuit in the sound source (such as CD, Walkma, etc.) , Resulting in pollution of the output audio, can be improved by the following methods: 1. Try to shorten the audio input lead; 2. Connect a 10uH high-frequency inductor in series between the two connections of the transmitter and the audio source; 3. Shield and isolate the audio source; 4. The most direct and effective method should be to reduce the output power or shorten the transmitting antenna. This method can be considered in the occasion of short distance transmission and high fidelity.
3. No vibration or weak oscillation; this fault is manifested in that the radio cannot receive static noise in the entire band, and the output power is small. If the quality of the component can be guaranteed, the following steps can help you troubleshoot: 1. At both ends of the CC Connect a 7pF capacitor in parallel (note: this capacitor should not be too large, otherwise you will find modulation failure); 2, adjust the bias resistance of the oscillation stage; 3, try to change the capacity of C6, if the above method can not be solved, it may be that the component layout is not Reasonably caused, the circuit board can be re-routed.
Fourth, the transmission distance is close: in addition to the common antennas placed improperly, the receiving sensitivity is low, and the use environment has tall buildings, etc., on the other hand, it is caused by weak oscillation, so it is still necessary to refer to the above operation to increase Crystal oscillator output strength. Another reason may be that the operating frequency of the frequency multiplier is not adjusted within the radio reception range. In fact, the radio receives only a weak harmonic signal. Its performance is that although the field strength meter is large, the effective transmission distance is very small. To 100 meters (under normal conditions, with a good radio, the open range is about 500-800 meters). For enthusiasts without frequency measuring instruments, in order to solve this kind of problem, in addition to the resonance inductance and capacitance should be selected in strict accordance with the above parameters, sometimes the reader needs a careful and patient, believe yourself, after many adjustments , You will solve all difficulties.

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[Photo] Talking about the production and debugging of FM transmitter

In various radio production projects, FM transmitters have been received by many enthusiasts ...

Published on 2006-04-15 20:48 â€¢ 233 views

[Photo] Talking about the production and debugging of FM transmitter

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2.54mm Female Pin Header

2.54mm (0.1") Pitch Female Headers
Overview
The most commonly seen female headers are 2.54mm (0.1") single or double row female/socket headers. These female headers together with its male counterpart are used in connecting Arduino boards and shields together. 2.54mm pitch female sockets/headers are low-profile connectors designed for signal and low power PC board connections when space is at a premium. They have the perfect height for clearing the USB-B connector and great for stacking multiple shields.
Since 2.54mm pitch female header is commonly used in a lot of applications, Scondar offers numerous options for this type of female header. Orientation can either be SMT or THM, single, dual or triple row. Antenk offers 2.54mm pitch female headers in either vertical or right-angle orientation. The pins and blades are also available in various sizes, counts, amperages, and plating.

The 2.54mm can accommodate a maximum current of 3A, with a 30 to 22 AWG wire size, and up to 40-positions. Antenk offers these female headers in high quality and affordable China-quoted price that snuggly fits with the pins of a male header and acts as a receptacle.

Female header always called as [Header connector", Antenk provide widely range of header connector, from 2.54mm (.100â€³ inch) pitch to 1.0mm (.039â€³ inch) pitch. The number of pins (contacts) is from 2 to 40 pins per row. There are three type: Straight (Dip Vertical), Right angle, SMT (surface mount).
If you can not find the items you interest from above items, welcome to contact us, and you will always get fully responsive from us.

Applications of 2.54mm Pitch Female Headers
Electronics:
LED applications
Arduino boards
Arduino Pro
Arduino Mega
Solar applications
Weighing systems

Appliances:
Air conditioner
Refrigerator
Microwave oven
Washing machine
Water heater
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Washer/Dryer
Stove
Automotive, Heavy Duty Military and Marine
For densely packed equipment requiring weight reduction and downsizing and for tough and harsh conditions.

Vehicle infotainment
Computer peripherals
Battery Connections
Battery connections rely on the ability of the current to pass reliable and solid current. This prevents overheating in the circuit and voltage drop.
Rechargeable battery packs
Battery balancers
Battery eliminator circuits
Medical Diagnostic and Monitoring equipment

Heart monitors

Communications
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Mount Type: Through-hole vs Surface Mount

At one side of this female header is a series of pins which can either be mounted and soldered directly onto the surface of the PCB (SMT) or placed into drilled holes on the PCB (THM).

Through-Hole (Poke-In)

Best used for high-reliability products that require stronger connections between layers.
Aerospace and military products are most likely to require this type of mounting as these products experience extreme accelerations, collisions, or high temperatures.
Useful in test and prototyping applications that sometimes require manual adjustments and replacements.
2.54mm, 1-row vertical female header, 2.54mm, 2-row vertical female header, 2.54mm, 3-row vertical female header, 2.54mm, 1-row right-angle female header and 2.54mm, 2-row right-angle female header, 2.54mm U-
Shaped Female header, 2.54mm U-Shaped Dual Row Female header are examples of Antenk products with through-hole mount type.

Surface-Mount
The most common electronic hardware requirements are SMT.
Essential in PCB design and manufacturing, having improved the quality and performance of PCBs overall.
Cost of processing and handling is reduced.
SMT components can be mounted on both side of the board.
Ability to fit a high number of small components on a PCB has allowed for much denser, higher performing, and smaller PCBs.
2.54mm, 2-row right-angle female header and 2.54mm, 1-row right-angle female header are Antenk`s featured SMT female headers.

Orientation/Pin-Type: Vertical (Straight), Right-Angle and U-Shaped

2.54mm pitch female headers may be further classified into pin orientation as well, such as vertical or straight female header, right-angle female header or U-shaped female header.

Vertical or Straight Female Header Orientation
One side of the series of pins is connected to PCB board in which the pins can be at a right-angle to the PCB surface (usually called "straight" or [vertical") or..

Right-Angle Female Header Orientation
Parallel to the board's surface (referred to as "right-angle" pins).
U-Shaped Female Header Orientation
U-shaped orientation is characterized by the shape of the pins at one side of the header, forming a letter [U". It is often chosen for applications where repeat mating cycles are not required as it can also be used and soldered directly to both PCB's.
Each of these pin-types have different applications that fit with their specific configuration.

Single, Dual or Multiple Number of Rows
For a 2.54mm straight or vertical female header, the standard number of rows that Antenk offers ranges from 1 to 2 rows. However, customization can be available if 3, 4 or n number of rows is needed by the customer. Also, the number of contacts for the single row is about 2-40 pins while for dual row, the number contacts may vary from 2-80 pins.

Pin Material
The pins of the connector attached to the board have been designed with copper alloy. With customer`s demand the pins can be made gold plated.

Custom 2.54mm Pitch Female Headers
Customizable 2.54 mm pitch female headers are also available, making your manufacturing process way faster as the pins are already inserted in the headers, insulator height is made at the right size and the accurate pin length you require is followed.
Parts are made using semi-automated manufacturing processes that ensure both precision and delicacy in handling the headers before packaging on tape and reel.

Tape and Reel Packaging for SMT Components
Antenk's SMT headers are offered with customizable mating pin lengths, in which each series has multiple number of of circuits, summing up to a thousand individual part number combinations per connector series.
The tape and reel carrier strip ensures that the headers are packaged within accurately sized cavities for its height, width and depth, securing the headers from the environment and maintaining consistent position during transportation.
Antenk also offer a range of custom Tape and reel carrier strip packaging cavities.

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