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# Circuit Diagram

## Index 268

### RF Power Meter

Published:2012-11-15 0:49:00 Author:muriel | Keyword: RF , Power Meter

### RF Field Strength Meter with Attenuator up to 200 MHz

Published:2012-11-15 0:48:00 Author:muriel | Keyword: RF, Field Strength Meter , Attenuator, 200 MHz

RF Field Strength Meter with Attenuator up to 200 MHz The RF field meter unit is a great help to tune transmitters for best performance and output power. You can measure the radiated energy field and can easy tune the system for max output field strength maximum power. This field strength meter comes with selectable attenuator. You can use it for measuring the antenna gain and pattern, compare different magnetic field strengths. See the following RF field strength meter schematic.   (View)

### RF Field Strength Meter

Published:2012-11-15 0:47:00 Author:muriel | Keyword: RF , Field Strength Meter

Most transmitter has several variable capacitors which are used to match impedance for transistors and antennas. I know people hate trimmers and so did I. The reason is that it is difficult to trim a system if you can't measure the performances. To trim a transmitter you need to measure the output power. Most transmitter are tuned with a dummy load of 50 ohm to substitute an antenna of 50 ohm. Not everyone has a power meter, and how can you know that the antenna you connect is purely 50 ohm. If not, the hole trimming is waste of time! What you would like to do is to measure the radiated power out from the antenna you actually are going to use. If you can measure the radiated energy field you can easy tune the system for max output field strength (max power). So, how can we measure the radiated energy field? The block diagram at right show you one easy way to measure the RF filed strength. To the left you find a dipole antenna. The antenna should be cut to match the receiving frequency ...   (View)

### RF Buffer Stage

Published:2012-11-15 0:46:00 Author:muriel | Keyword: RF , Buffer Stage

This bufferstage is intended to be used after a BF900 or BF199 (even a BF245) oscillator. It delivers several milliwatts and is perfect to drive a 2N2219 or 2N4427. Be sure the coils are really round and can see each other: place metalplates between the coils. The supply voltage is around 12V (typ. 13,8V).   (View)

### Remote control using VHF modules

Published:2012-11-15 0:45:00 Author:muriel | Keyword: Remote control, VHF modules

A few designs for remote control switches, using VG40T and VG40R remote control pair, are shown here. The miniature transmitter module shown in Fig. 1, which just measures 34 mm x 29 mm x 10 mm, can be used to operate all remote control receiver-cum-switch combinations described in this project. A compact 9-volt PP3 battery can be used with the transmitter. It can transmit signals up to 15 metres without any aerial. The operating frequency of the transmitter is 300 MHz. The following circuits, using VG40R remote control receiver module measuring 45 mm x 21 mm x 13 mm, can be used to: (a) activate a relay momentarily, (b) activate a relay for a preset period, (c) switch on and switch off a load.   (View)

### Ramsey 25 BA1404 Stereo FM Transmitter

Published:2012-11-15 0:45:00 Author:muriel | Keyword: Ramsey , 25 , BA1404 , Stereo , FM, Transmitter

Stereo FM transmitter based on BA1404 and 145170 frequency synthesizer IC.   (View)

### Radio Remote Control using DTMF

Published:2012-11-15 0:44:00 Author:muriel | Keyword: Radio, Remote Control , DTMF

Here is a circuit of a remote control unit which makes use of the radio frequency signals to control various electrical appliances. This remote control unit has 4 channels which can be easily extended to 12. This circuit differs from similar circuits in view of its simplicity and a totally different concept of generating the control signals. Usually remote control circuits make use of infrared light to transmit control signals. Their use is thus limited to a very confined area and line-of-sight. However, this circuit makes use of radio frequency to transmit the control signals and hence it can be used for control from almost anywhere in the house. Here we make use of DTMF (dual-tone multi frequency) signals (used in telephones to dial the digits) as the control codes. The DTMF tones are used for frequency modulation of the carrier. At the receiver unit, these frequency modulated signals are intercepted to obtain DTMF tones at the speaker terminals. This DTMF signal is connected to a DTMF-to-BCD converter whose BCD output is used to switch-on and switch-off various electrical appliances.   (View)

### Prescaler with Counter

Published:2012-11-15 0:43:00 Author:muriel | Keyword: Prescaler , Counter

Digital frequency counter is being used for wide range of applications. Digital frequency counter extensively uses digital circuits and hence fairly good knowledge of digital circuits and of digital integrated circuits is required to understand the operation of the frequency counter. However a person who is not familiar with any electronics circuits and experiments has in written this article.   (View)

### PLL Stereo FM Transmitter

Published:2012-11-15 0:41:00 Author:muriel | Keyword: PLL, Stereo , FM, Transmitter

### PLL FM Transmitter using LMX1601, ATtiny2313 AT90S2313

Published:2012-11-15 0:37:00 Author:muriel | Keyword: PLL, FM Transmitter, LMX1601, ATtiny2313, AT90S2313

Here's a PLL FM Transmitter using LMX1601, ATtiny2313 or AT90S2313 microcontrollers. The common characteristic of all of the previous low power FM transmitters I've built over the decades, is that their operating frequency is determined by an LC resonant circuit. Some of them had excellent stability, some of them didn't, but I had always wanted to make one that is crystal controlled. Various schemes had been considered from time-to-time, including the direct approach of modulating the load capacitance of a a crystal oscillator, a whimsical phase modulation scheme involving a phase shifter, some balanced modulators, and limiting amplifiers, and at times, the down-to-earth and sober approach of modulating a VCO within a phase locked loop (PLL). While browsing Digikey's online catalog, I found the LMX1601 frequency synthesizer chip and thought: Just maybe, the PLL approach is finally within my grasp. The LMX1601, which apparently was designed for use in cell phones, includes everything need to make two phase locked loops except for the VCOs. More importantly, one of the PLLs, specifically the AUX PLL, is specified to work in the FM broadcast band. The LMX1600 and the LMX1602 were also considered, but the LMX1601 was selected because it has a 500 MHz option , meaning that it can work down to about 50 MHz. An LMX1601 Phase locked loop, a discreet FET VCO, and an AVR micro controller combine to make a stable, easy to use monophonic FM transmitter that includes a an audio activated switch that turns the transmitter on only when its being used. With the LED lit blue to indicate the transmit mode, the transmitter's user interface is clean and simple. Two push buttons step the frequency up and down. The transmitter comes one when audio of sufficient amplitude is applied, and stays on for five minutes after the audio drops below the threshold. The LED flashes red briefly to show when audio is detected, so I know if the volume of the audio signal is high enough. A small hole under the LED is for the piezoelectric transducer, whose main job is to produce key clicks when the frequency increment and decrement buttons are pressed. The buttons do not provide tactile feedback. The painful part was dealing with the packaging of the chip. The lead centers of this 16 pin package are only 0.65 mm apart. Dealing with the fine printed circuit board features that would be needed to mount this chip was the most daunting aspect of using the chip. I had only experimented with the laser printer toner etch resist method of making PC boards a few months earlier, with some success. As it turned out, the laser printer toner etch resist method could be pushed to make a board that supports this chip. But just barely.   (View)

### PLL FM Transmitters

Published:2012-11-15 0:31:00 Author:muriel | Keyword: PLL, FM , Transmitters

This is PLL FM Transmitter using SAA1057 chip. Transmitter can be operated from a PC through LPT port, or using a PC software as a driver.   (View)

### PLL Exciter-2

Published:2012-11-15 0:30:00 Author:muriel | Keyword: PLL Exciter

This is a PLL controller that works with the VCO/Modulator that I designed. Use these two modules together for a complete baseband-capable exciter unit. This PLL controller features a rock-stable crystal controlled reference, in conjunction with a programmable dividing network which allows the transmitter to be tuned in 100Khz steps from 79.9Mhz to 109.7Mhz by means of digital thumbwheel switches.   (View)

### PLL Exciter

Published:2012-11-15 0:29:00 Author:muriel | Keyword: PLL Exciter

This is a PLL controller that works with the VCO/Modulator that I designed. Use these two modules together for a complete baseband-capable exciter unit. This PLL controller features a rock-stable crystal controlled reference, in conjunction with a programmable dividing network which allows the transmitter to be tuned in 100Khz steps from 79.9Mhz to 109.7Mhz by means of digital thumbwheel switches.   (View)

### Phone Spy Transmitter

Published:2012-11-15 0:29:00 Author:muriel | Keyword: Phone, Spy, Transmitter

Here is a very simple telephone broadcaster transmitter which can be used to eavesdrop on a telephone conversation. The circuit can also be used as a wireless telephone amplifier. One important feature of this phone transmitter is that the circuit derives its power directly from the active telephone lines, and thus avoids use of any external battery or other power supplies. This not only saves a lot of space but also money. It consumes very low current from telephone lines without disturbing its performance. The phone bug transmitter is very tiny and can be built using a single -IC type veroboard that can be easily fitted inside a telephone connectin box of 3.75cm x 5cm. The spy phone transmitter consists of two sections, namely, automatic switching section and FM transmitter section. Spy phone transmitter circuit diagram Phone Spy Transmitter Automatic switching section comprises resistors R1 to R3, preset VR1, transistor T1 and T2, zener D2 and diode D1. Resistor R1, along with preset VR1, works as a voltage divider. When voltage across the telephone lines is 48V DC, the voltage available at wiper of preset VR1 ranges from 0 to 32V (adjustable). The switching voltage of the circuit depends on zener breakdown voltage and switching voltage of the transistor T1. Thus, if we adjust preset VR1 to get over 24.7 volts, it will cause the zener to breakdown and transistor T1 to conduc. As a result collector of transistor T1 will get pulled towards negative supply, to cut off transistor T2. At this stage, if you lift the handset of the telephone, the line voltage drops to about 11V and transistor T1 is cut off. As a result, T2 gets forward biased through R2 to provide a DC path for T3 used in the following FM transmitter section. The low-power FM transmitter section comprises oscillator transistor T3, coil L1 and a few other components. T3 works as a common-emitter RF oscillator, with T2 serving as an electronic 搊n/off� switch. The audio signal available across the telephone lines automatically modulates oscillator frequency via T2 along with its biasing R3. The modulated RF signal is fed to the antenna. The telephne conversation can be heard on an FM receiver remotely when it is tuned to the transmitter frequency.   (View)

### Miniature FM Transmitter

Published:2012-11-15 0:28:00 Author:muriel | Keyword: Miniature, FM , Transmitter

This miniature transmitter is easy to construct and it's transmissions can be picked up on any standard FM receiver. It has a range of up to 1/4 of a mile or more. It is great for room monitoring, baby listening, nature research, etc. L1 is 8 to 10 turns of 22 gauge hookup wire close wound around a non-conductive 1/4 inch diameter form, such as a pencil. C4 is a small, screw-adjustable, trimmer capacitor. Set your FM receiver for a clear, blank space in the lower end of the band. Then, with a non-conductive tool, adjust this capacitor for the clearest reception. A little experimenting and patience may be in order. Most of the parts' values are not critical, so you can try adjusting them to see what happens. FM Transmitter Parts: R1, R4, R6 10K resistor R2 1Meg resistor R3 100K resistor R5 100 ohm resistor R7 1K resistor C1, C2 0.1uf capacitor C3 0.01uf capacitor C4 4-40pf variable capacitor C5 4.7pf capacitor Q1, Q2 2N3904 transistor L1 8-10 turns of 22gauge wire around non-conductive 1/4 diameter form Elec Mike Electret Mic   (View)

### Mini FM Transmitter

Published:2012-11-15 0:27:00 Author:muriel | Keyword: Mini , FM , Transmitter

9 Volt battery operated simple Mini FM Transmitter. FM Transmitter is very simple, compact, and has transmission signal with a range of 100-150m, good sensitivity and low current consumption. Transmitter's schematic consists of a bass amplifier for the first transistor and the proper frequency generator in the second. FM Transmitter divided transitional capacitor that allows you to set up a cascade separately. Transmitter PCB shows the value of all the details and transistors! Reel contains 5 turns enameled wires 0.35mm to send a diameter of 3.2mm (rod of the handle). Setting frequency boils down to the installation shown in the pattern of voltages through appropriate resistors, and then check the current consumption � it should be about 10mA antenna � a piece of wire 40cm. Here you can see the bug assembly factory performance. FM Transmitter uses very small PCB and some SMD resistors.   (View)

Published:2012-11-15 0:27:00 Author:muriel | Keyword: Mini, FM, Radio, Transmitter

This small FM transmitter with a range of about 50 meters designed for hoby. With lots of mini-transmitters then you have a comprehensive, action-packed radio program. Due to the power supply via the USB port of a high frequency stability is achieved. Alternatively, the receiver, a battery 5 to 12 volts to operate. Mini FM Radio Transmitter circuit with BF199. Tags: BF199, Mini fm radio Transmitter circuit, radio transmitter circuit, rc transmitter circuit, receiver circuit, rf transmitter circuit, small FM transmitter, transducer circuit, transistor circuit, video transmitter circuit, wireless transmitter circuit   (View)

### Micro Spy PLL FM Transmitter

Published:2012-11-15 0:26:00 Author:muriel | Keyword: Micro, Spy, PLL , FM, Transmitter

This micro spy PLL FM Transmitter transmits on the 160MHz frequency (if we use a 40MHz quartz) and therefore can be listened through a receiver tuned on this frequency. This circuit can be used to on various frequencies, for example on the FM band 88-108 just modifying some components, among which the quartz (25MHz). Voice is detected by an electret microphone, then it is amplified and filtered by U1 pass-band in order then to be modulated from the carrier section, where through the varicap diode it mixes with the frequency generated by the quartz, that guarantees an adapted stability. Practically the modulating voltage is obtained applying the audio signal to the resonating circuit varicap diode that determines the carrier oscillation. The carrier frequency (160 MHz) must be greater than the modulating frequency (300-3300 Hz) audio band. The transmission is on the fourth harmonic, therefore 160MHz, the oscillation frequency of the driver RF transistor Q1. A small calibration is allowed acting on the L1 inductance and the C1 Trimmer Capacitor.   (View)

### LowPass Filter

Published:2012-11-15 0:23:00 Author:muriel | Keyword: LowPass Filter

The schematic you find here comes from another site on the internet, but because it's on so many sites, we don't know who actually designed it. However it's a nice one. Capacitors: C1,C4 22pF cer. C2,C3 51pF cer. Coils: L1,L2,L3 #18 bus wire, 1/4 diameter, 3 turns * Form the leads from the capacitors as shown in the little figure below. Then solder them from the pad to the outside ground area. * Be sure that the turns from the coil are seperated by the same distance as the diameter of the wire * Form the leads from the coils as shown in the little figure below. Then solder them in place. * Place the filter in a metal box, with rf-connectors on both ends ( SO239(=PL259), BNC or N-connectors)   (View)

### Low Pass Filter For FM 88-108 MHz

Published:2012-11-15 0:22:00 Author:muriel | Keyword: Low Pass , Filter, FM , 88-108 MHz

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