Blog Title: The Broadcast Electronic

470-580 MHz UHF TV Transmitter

TV transmitter requires supplies voltage of 9-15 Volt. However, you can also use a 9v batteries.

This is an important thing to remember for building of the tv ransmitter circuit is that the dimensions of coil size to match the frequency of the desired work. The value of the spindle is making coil as follows:
L1, L2 = 3 Turns, diam. 3mm, 0.5mm wire
L3 = 2 Turns, diam. 3 mm, 0.5 mm wire


More detail 470-580 MHz UHF TV Transmitter

VHF Video Transmitter for Camera

Transistor components that are used for a video transmitter is BC548 or you can use another type of transistor BF199. Meanwhile, other passive components used SMD type. For winding coil L1 is 5 Turns 8 mm in diameter and use wire AWG 0.3-0.5 mm.

Once you up the circuit this video transmitter, antenna use as a cable along the 50 cm. To determine the frequency of work, turn the trimmer capacitor 22 pf accordance with the frequency that you want.

More detail for VHF Video Transmitter

Audio Limiter/Compressor for Electret Desk Microphones

This electronic circuit is audio limiter compressor specifically designed to use with very low-cost electret desk microphones. Overcomes the heavy attack/decay problems with diode rectifier VOGAD circuits.

A TL074 IC was used with a dual supply of +/-5v Note the lack of rectifier diodes in the feedback loop, instead the circuit uses high gain BC848(smd BC108) This uses the full wave rectifier effect to give a non-linear compression level avoiding the worst of the 'pumping' normally noticed with discrete diodes. R38 sets the compression level/bias point to suit the hfe of the selected transistor. Note Q2 is a P channel Junction FET eg J176.

Source: http://www.g8ajn.tv/projects.htm

RF Power Meter

The RF Power Meter presented is based on the AD8313 Log Detector manufactured by Analog Devices. The IC can be ordered as a sample direct from ADI, or you can search for it in some disabled GSM mobile phones available on the market. In GSM phones AD8313 is used as a Log Detector, part of the Power Control Loop circuit. Generally could be easy identified near the Power Amplifier module.

AD8313 is a Logarithmic Detector which can accurately convert an RF signal at its input to an equivalent decibel-scaled value at its DC output.

The DC output is “linear in dB” with a basic slope of 20mV/dB. The slope can be adjusted in a range from 18mV/dB to 30mV/dB. The linear input range of AD8313 is between -60dBm and 0dBm, which corresponds to a DC output between 0.6V to 1.6V (pin 8).

The following operational amplifiers (LM324) are translating the DC output range of AD8313 (0.6V to 1.6V on Pin nr 8) to a scaled range read by the Voltmeter (-6V to 0V). The scaled range has a resolution of 100mV/dB.

For example the minimum input value (-60dBm) corresponds to a read voltage value of -6.0V, -59dBm corresponds to -5.9V, -58dBm corresponds to -5.8V, and so on up to 0V that corresponds to 0dBm (as in the table below).

The frequency range of AD8313 is between 100MHz to 2.5GHz, but the range that not requires a dynamic slope adjustment is between 100MHz to 1.4GHz. The resolution of the RF Power Meter is better than 1dB; only near 0dBm input is approximately 2dB. The RF input has an impedance of 50 ohms provided by the 53 ohms resistor in parallel with the internal impedance of the AD8313.

For calibration inject first at the input an 800 MHz signal at -60dBm and adjust P2 for -6V reading on the output Voltmeter. After that increase the input level up to 0dBm and adjust P3 for 0V reading on the output Voltmeter. The slope can be adjusted by the P1 semi-resistor.

Careful design of the RF input layout should be done for minimizing parasitics which can produce un-wanted resonances that affects the linearity vs frequency of the log-detector.

Tolerance of the resistors is +/-1%.

A calibrated attenuator at the input can be used to increase the maximum input power, without damaging the detector.

Low Power TV Transmiter

One of the most useful gadgets a video enthusiast can have is a low-power TV Transmitter. Such a device can transmit a signal from a VCR to any TV in a home or backyard. Imagine the convenience of being able to sit by the pool watching your favorite movie on a portable with a tape or laserdisc playing indoors. You could even retransmit cable TV for your own private viewing. Videotapes can be dubbed from one VCR to another without a cable connecting the two machines together.

RF Spectrum Analyzer

Below is a two part project for an RF Spectrum Analyzer from QST Magazine. Even if you don't build the project there's some great information in here regarding RF filters, mixers, oscillators and more.

Spectrum Analyzer (Part One)

A mong the many measurement tools sought by the amateur experimenter, the most desired but generally considered the least accessible—is the radio-frequency spectrum analyzer or SA. This need not be simple and easily duplicated, this homebuilt analyzer is capable of useful measurements in the 50 kHz to 70 MHz region. The design can be extended easily into the VHF and UHF region with methods outlined later. The instrument is configured to be self-calibrating, or capable of calibration with simple home-built test gear.







Spectrum Analyzer (Part Two)

One use for a spectrum analyzer is amplifier evaluation. We can illustrate this with a small amplifier from the test-equipment drawer—an old module that has been pressed

into service for a variety of experiments. This circuit, shown in Figure 11, is used for illustration only and is not presented as an optimum design. It’s a project that grew from available parts and may be familiar to some readers. The circuit uses four identical 2N5179 amplifier stages. A combination of emitter degeneration and parallel feedback provides the negative feedback needed to stabilize gain and impedance. (Ideally, construction and measurement of a single stage should precede construction of the complete amplifier.)

70-210 MHz RF Oscillator Circuit

The RF Oscillator is based on a Hartley oscillator. The frequency is determined by L1 and capacitor C1. The Vtuning voltage will change the capacitance in the varactor BB132 wich will change the oscillation-frequency. The value of capacitor C2 will determine how much the frequency can be changed by the tuning voltage. The larger value the more the frequency will change.

This Oscillator Circuit is based on two dual-gate FET. First FET is a Hartley oscillator where the frequency is determined by the value of L1, C1, C2 and the varicap diod. C2 set the span of the VCO. The second FET is just an amplifier. The gain is less than 1, but the current will be higher and the oscillator will not be loaded. The output amplitud changes depending on the frequency and how many turns there is on L1. By changing the voltage on g2 at FET1 you can set the amplitud. By adding a resistor to ground you will lower the amplitudo.


In this schematic I have conected g2 to Vcc (through R1) wich will give the highest gain.

VCO have made some test with different coils. The diameter of L1 is the same 7.2mm
but I have changed the turns to 3, 4 and 5. The diagram at the right shows the Amplitudo and the frequency. You can also se the range of this VCO. During the test the varicap was removed so the tuning range is set by C1. The best way to get the oscillator work is to attach a oscilloscope to the output. If the amplitud of the oscillator is low, you must move the tap-point a bit. The best way is to make 3-4 coils with the tap-point at different places and test each coil before you decide wich one you will use. The amplitud from my VCO is about 200mVRMS at 100MHz.


Remember: When you are building oscillator you must keep the wires short and shiled the oscillator! then it will work nice.

1W FM Amplifier For Ipod FM Stereo Transmitter

The schematic show you a RF amplifier with very high gain. The feeding RF signal enter C9 to transistor Q1 which has a self biased working point. The gain and working point is set with the two resistors R1 and R2. FB1, C5, C6 works as filter for rejecting RF to power line. Q1 has a gain about 15dBm. The output signal can be found a the collector which then enter a second amplifier stage Q2. This stage also has a self biased working point.

The gain is set by the resistors R3//R4 and R5//R6.


Why do I have 2 parallel resistors like that?
It is because I want to be able to change the gain of the amplifier. On the PCB below you will see that I only have 2 pads for the resistors. When I want to resistors I solder the two resistors R5 and R6 on top of each other and the same with R3 and R4.

I advice you to start building without R3 and R5 and test the unit. If you want you can then add R3 and R5 later to obtain max gain of this stage.
Q2 has a gain of 12 dBm. FB2, C7, C8 works as filter for rejecting RF to power line.

The last amplifier stage is based around the transistor 2N3866. This transistor has low input impedance.


I match it by using 2 capacitors (C11, C12) and the inductor L1 to about 50 ohm. The transistor has an output impedance match, (C13, C14, and L3) to get best performance for an 50-75 ohm antenna.

- The inductor L1 is made by a wire 2 turns with 5mm diameter.
- The inductor L2 is made by a wire 7-9 turns with 6.5mm diameter.
- The inductor L3 is made by a wire 4 turns with 6.5mm diameter.

L4 is a Axial Lead Bead, which reject RF very good and has low resistance. You can use almost any choke or large inductor for L4, it is not a critical component.
The FM transmitter require 2 AAA batteries and consume about 38mA.
To get rid of batteries, I have added a voltage regulator IC1, to the PCB which deliver 3.3V to the FM transmitter unit.

The PCB is mirrored because the printed side should be faced down the board during UV exposure.
To the right you will find a pic showing the assembly of all components on the same board.
This is how the real board should look when you are going to solder the components.
It is a board made for surface mounted components, so the copper is on the top layer.


Grey area is copper and each component is draw in different colours all to make it easy to identify for you. The scale of the pdf is 1:1 and the picture at right is magnified with 4 times.

Download PCB mirror, Schematic-Component Mounted Visit Page

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150 WATT FM AMPLIFIER BASED SD1407

Working frequency of this fm amplifier is 88-108 MHz VHF band II and Power supply voltage 18-28 VDC.



Download : schematic, PCB all layer, top layer, bottom layer. More info ...

MC145151 PLL FM Stereo Transmitter

This transmitter use pll chip MC145151 from Motorola and stereo encoder chips BA1404 with vco built in. BA1404 from MC145151 is to overcome the single-frequency instability in the BA1404. Modulation of the emission control BB910 frequency. B571C kept in control procedures, the procedures required to prepare another.

Amplifier section of this FM Stereo transmitter use 2sc2053 with power 250 mWatt out.

300mW FM Transmitter 2SC2538

The FM transmitter using a varactor diode way radio, plus a Class C amplifier, RF output power of up to 300 mW more open to more than one kilometer distance communications. Select components: Q1 with ≥ 100 mA, Ft ≥ 300 MHz, β ≥ 100 tubes available 3 DG82, 3DG122, 3DG130, 2G711; Q2 with 2SC2538, 2SC1970, etc.. It must be noted that RF Baffles circle L8, L9, L10; C13, C14, C17, C18, C19, and so can not be omitted, otherwise it would cause unnecessary self-excited oscillation.

L1, L5 need to tap extraction, data such as icons, not otherwise due to impedance matching, the output power of less than maximum. Such as a battery-powered, Q3 (Darlington tube), C15, R6 can be omitted. ebugging steps: first in the output termination of testing circuit to regulate the C7, C9, C12 to the largest multimeter readings, remove test circuit connected to one meter in length pole antenna to pull to fine-tune C12 simple reading of the largest field will be completed debugging.

PLL FM Transmitter With BH1415F 500mW

This article is wang1jin (Old: Primary Color love) for the design of RF EDNCHINA.COM FM transmitter board for further analysis, making friends for reference. This EDNCHINA PCB board can be free. Need friends can make reference to relevant websites Learn more.

Designed with PLL technology, BH1415 FM transmitter system block diagram, LCD1602 from STC2052 - M62429 MIC - BH1415 infrared keyboard amplification and high frequency components.
(Website procedural reasons, the picture may not clear to the local Save Show) More info ...

High Quality wireless microphone Macsot MR-700

This is collected by the Macsot MR-700 wireless microphone system launch of the circuit for maintenance reference. High Quality Audio on receiver output.

Active components:

• Microphone or Audio Preamplifier with IC MC4458
• Dynamic Audio processed with one NE571 From Philips
• Frequency Oscillator generated by one crystal 20.05 MHz and Varactor diode 2CB11A. No drift frequency is guaranted.
• 9V DC power supply or battery. More info ...

CD4066 FM Stereo Encoder

Circuit schematics IC1-4069 in the Y1, Y2 formation of a 76 KHZ frequency of the oscillator, the Y3-Y6 isolation plastic, into IC2 dual JK flip-flop CD4027 composed of two components- frequency circuit, a symmetrical + / 38KHZ-19 KHZ and the square wave, + / -38 KHZ IC3 the square used to control analog switches CD4066, a stereo audio input signal after switching modulation used for the 19 KHZ frequency mixed signal to the transistor into FM 9014 after isolation Modulator.

Click to access the debug FM modulator and 5 V power supply, with a multimeter measured IC1 CD4069 the legs and IC2 CP, Q, Q, the legs should be half the supply voltage, the oscillator has been start-up. If a digital frequency meter measured IC1 output frequency, frequency regulation RW1 to 75 KHZ + /-10HZ can. If not, can be transferred to the prospective radios, RW2 half-good, and then transferred RW1, the bright lights stereo radio, and no speakers in the temple frequency whistle sounds. From the input into the stereo audio signal (1.5 Vpp, output amplifier available), this will be able to receive stereo radio broadcasting.

Input signal can be obtained from the line, but at R7 should be changed. Finally, can be transferred R7 to the smallest high-frequency noise, in fact R6, R7 equivalent BA1404 in 13, 14 feet of external components, the Pilot mixed signal and composite signal circuits, and input to the amplifier, the circuit of is 9014, and BA1404 from 12 feet on the entry. More info ...

uPC1651 FM transmitter

The circuit has been produced by Japan's NEC as a major upc1651 IC devices, the high gain circuit, work stability, thereby ensuring the microphone performance. Use of FM transmitter.

Used it 40 - 50 cm soft drag line for antenna, the effective range of more than 30 launch M. L carefully spacing adjustment and fine-tuning capacitor, will launch frequency coverage for 88 - 108 Mhz. Map L enameled wire with diameter of 0.51 mm in diameter, 4 mm cylindrical Tuitai from around 5 laps. More info ...

FM Transmitter With Transistor 2SC1815

I Will have to introduce a system of simple and small FM transmitter. Not only does it meet the requirements of the launch distance, but also at the same time using microphone and voice input signal line, background voice. Modulation circuit surveillance has also joined the table first,

so that they can better control and the proper use of transmitters, the following circuit diagram, read briefly, whether it's just like a radio station equipment as many functions. Yes, this small transmitter can help you easily set up an amateur FM radio stations! 500 M in the coverage around. Echocardiography the bar, act immediately!



Principle smallFM transmitter circuit components and options:

Signal to the microphone after intake, the C1 coupling into the BG1 and external circuit voltage of the single negative feedback amplifier, the voltage signal amplification weak enough to enlarge the extent of U1A and the line to enter the input signal with a mixed U1B. Mixed signal modulation way to the R17 from BG2 FET and the surrounding circuit composed of common than LC finishes the test, the test than the LC oscillator are characterized by a general three-capacitance oscillator simple, but also with high efficiency and high stability. Waveform, and modulation bandwidth, as this amateur production of FM transmitters appears to be particularly important. Finally BG3 cast by the post-amplifier to enlarge the field by launching antenna fired by general can listen to FM radio broadcast. Another component of the signal through the amplifier to enlarge U1C after the wave rectifier D2 SR DC drive microamps table, Near and surveillance signal modulation rate. Use the system for general should not exceed 85 per cent suitable. GM and other integrated circuits using LM324 four operational amplifier and form a single power reverse input, both of the input voltage is set at half the supply voltage. Table surveillance for the first u-200, BG1.BG3 choose 2SC1815. BG2 three DO2 FET, D2 varactor diode using a S2267. Antenna require the use of 1 / 4 wavelength, such as the use of the best pull rod antenna not less than one metre. Otherwise effect will be less than overstaying launch. Final say about, please do not interfere with normal radio! More info ...

Making Simple TV transmitter

(1) Soundless version

You are familiar with the most simplest FM transmitter that I designed. Let's try to transform it into a TV transmitter. Just change the input from the audio to the video (video camera or VCR) and check the signal at your television set: in Europe, for instance, choose the channel 2 - 4 and turn the trimmercap at the transmitter.

You will find some images or might watch a clear image. This suggests that it will be not so difficult to build a TV transmitter.

(2) Advanced Version (AV)

When you succeed in this version to work, you may try the advanced version (pdf). In this version, stability and quality are improved. This can have even the audio too. However, in order to complete this, you have to use a proper frequency counter. More info ...

Preamplifier 88-108 MHz

This VHF amplifier working on Band 2 Radio Spectrum tuning approximately 88 - 108 Mhz
The Preamplifier circuit uses two 2N3819 FET's in cascode configuration. The lower FET operates in common source mode, while the upper FET, operates in common gate, realising full high frequency gain. The bottom FET is tunable allowing a peak for a particular station.

Coil details follow:
L1 4 turns of 18swg air spaced with a 1cm diameter, the tap is one turn up from earth end...
L2 4 turns of 18swg air spaced with 1 cm diameter. The coupling coil is 1 turn interwound from the supply end. Enamel coated wire must be used. More info ...

Microphone FM Transmitter

This simple transmitter operates from a 9V battery as shown above. The old FM mic system was not a perfect solution, so I built this kit and a mixer for the receivers. using three separate transmitter circuits and a mixer on the receiever, the choir voices were perfect and cleanly reproduced."

From the notes I made experimentally, C3 is vital to the circuit and without it the circuit may become unstable. C4 is in parallel with C5 and presents a moderate load impedance. Finally all transistors are NPN. The circuit works well and has proved reliable. More Info ...

FM Transmitter with 4 Transistors

This circuit provides an FM modulated signal with an output power of around 500mW. The input Mic preamp is built around a couple of 2N3904 transistors, audio gain limited by the 5K preset. The FM Transmitter oscillator is a colpitts stage, frequency of oscillation governed by the tank circuit made from two 5pF capacitors and the inductor. Frequency is around 100Mhz with values shown.

Audio modulation is fed into the tank circuit via the 5pf capacitor, the 10k resistor and 1N4002 controlling the amount of modulation. The oscillator output is fed into the 3.9 uH inductor which will have a high impedance at RF frequencies.

The output stage operates as a class D amplifier , no direct bias is applied but the RF signal developed across the 3.9 uH inductor is sufficient to drive this stage. The emitter resistor and 1k base resistor prevent instability and thermal runaway in this stage. More info ...

Voice FM Transmitter Circuit

It is illegal in most countries to operate radio transmitters without a license so take care with transmitter circuits. This FM Low Power circuit may be tuned to operate over the range 87-108MHz band II, with a range of 20 or 30 metres.

Active components in this circuit are BC548 transistors. Although not strictly RF transistors, they still give good results. I have used an ECM Mic (Voice FM) insert from Maplin Electronics, order code FS43W. It is a two terminal ECM, but ordinary dynamic mic inserts can also be used, simply omit the front 10k resistor. The coil L1 was again from Maplin, part no. UF68Y and consists of 7 turns on a quarter inch plastic former with a tuning slug. The tuning slug is adjusted to tune the transmitter. Actual range on my prototype tuned from 70MHz to around 120MHz.

The aerial is a few inches of wire. Lengths of wire greater than 2 feet may damp oscillations and not allow the circuit to work. Although RF circuits are best constructed on a PCB, you can get away with veroboard, keep all leads short, and break tracks at appropriate points. More info ...

VHF UHF TV modulator

Simple TV Modulator that working on VHF UHF Band, the oscillator generates frequency is modulated with the video signal and the modulated carrier wave thus generated is fed into the TV set's aerial input via a cable. Then all that remains to do is tune the VHF UHF TV set to the correct frequency.

The harmonics generator converts the oscillator signal into a sort of frequency spectrum containing all the multiples of 27 MHz up to about 1800 MHz. The TV modulator's output signal is made up of a large number of little peaks, each of which is a complete transmitter signal. At least one of these will always be in band I (VHF channels 2. . . 4), one in band III (VHF channels S. . .12) and many of them will be in bands IV and V (UHF channels 21.. .69). More info ...

TV Transmitter Band I and III

This TV transmitter working on VHF Band I and III, using negative sound modulation and PAL video modulation. This is suitable for countries using TV systems B and G, like Australia and Indonesia. Band I (VHF Low) and Band III (VHF High).

This circuit has not been tested at UHF frequencies. The modulated sound signal contains 5.5 - 6MHz by tuning C5. Sound modulation is FM and is compatible with UK TV Transmitter System I sound. The transmitter however is working at VHF frequencies between 54 and 216MHz (band I and Band III) and therefore compatible only with countries using Pal System B and Pal System G. More info...

FET Audio Deviation Limiter

This applicationis a very high specification peak control limiter. It has fast become the essential deviation limiter for FM radio. Audio Limiter is a standard specification in broadcast world. This limiter can be set up as sound processor for fm broadcast.

The application divided into two parts :
1. Broadband Limiter


2. Splitband Limiter


Active component : FET 2N5457 and Ics NE5534, 2N5532, TL071 TL072.

Download schematic and component mounted in Coreldraw 12 Format.