The Broadcast Electronic

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

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

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

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.

When connected to a video camera, a TV transmitter can be used in surveillance for monitoring a particular location. The main problem a video enthusiast has in obtaining a TV transmitter is that a commercial units are expensive. However, we have some good news! You can build the TV Transmitter described here for less.

For Circuit Description and Construction please download here

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.)

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.