A transmitter is a device which generates high
frequency power, which, by means of a suitable
antenna, is radiated (or transmitted) through
space (or other suitable media). Transmitter
signal may be modulated with information, (noise,
voice, pictures (TV)). This modulation or
information may be received and demodulated in a
receiver, where the combination of a transmitter
and receiver is known as a radio system.All
carriers send over an RF signal are realy analog.
The informationon this carrier can be digital if
it is a digital broadcast that isbeing listened to
or viewed. The RF carrier is a sinusoidal type
wavewith very low distortion to avoid generating
harmonic interference toother frequencies used by
other stations. This carrier may be
frequencymodulated or amplitude modulated,
depending on the desired standard.Transmitters are
usually controlled by a low level oscillator, the
oscillators themselves being controlled by an LC
(Inductor-capacitor) circuit resonant at the
oscillator frequency, or by a quartz crystal. FM
modulation is normally achieved by the use of a
varactor diode, one which varies its capacity as a
function of the applied voltage. If an audio
voltage is applied, its capacity will follow the
AF variations. Thus, such a capacitor is used to
form part of an LC oscillator, or a quartz crystal
oscillatorAM may be achieved by feeding the output
from an audio amplifier to a transformer whose
secondary is in series with the supply line
feeding the RF oscillator (low level modulation)
or Power Amplifier (high level modulation) of the
transmitter. This adds to, or subtracts from, the
DC power feeding the transmitter, thus varying the
amplitude of the output as a function of the input
to the audio amplifier.Remeber that radio
transmitters need a permit to have and operateat
the give frequency. In some countries (USA) you
are allowed to dovery small power broadcasts if
you do not cause interferenceand stay within the
FCC limits. In other countries it might be
illegalto have this type of radio transmitter with
you (exceptions arecircuits for measurement
purposes which are packed in metal boxes anddo not
have antenna so can't be used for illegal
broadcasting).Remeber that if you operate a
radio transmitter without a permityou can get
quite high fines or go to jail in many countries.
Evenowning a radio transmitter without a permit is
illegal in manycountries. Check the local
legistlation before startingto build or use any
radio transmitter. You shouldcheck the law before
buying any transmitting equipment as a fine,
confiscation of equipment and/or imprisonment can
result from illegal use or ownership. The laws
vary from country to country, therefore check
local laws. General warning on radio transmitter
operation: Do not transmit until you have matched
the antenna connected to the radio transmitter. If
you have not connected the antenns, you can burn
out parts in the transmitter. Some transmitters
are better protected against antenna problems, so
if you try to transmit without antenna your luck
may vary if yoiu damage something or not.
- CB-Radio
Component Database
- Estimating
Transmitter Distance - Here you can find
a simplified equation for analysing low
power radio transmitters, for line of sight.
It does not take into account probagation
conditions or other limiting factors, but
does include a variable for the losses in
the antenna and tank circuit of a
transmitter.
- Hum
Reduction in FM Stereo Transmitters - It
is convienient and easy to use a wall
transformer with FM stereo or AM
transmitters, but often unwanted hum appears
on the transmitted signal. This problem can
be sometimes frustrating and difficult to
correct.
- To
Design and Build a Portable, Miniaturised,
Multichannel FM Transmitter
- UHF
Construction Precautions - If you are
building a kit or circuit that operates at
VHF (over 30 MHz) or UHF (over 300 MHz) you
should be made aware of proper wiring and
construction practices. This is largely
experience combined with a good theoretical
understanding.
- VHF
Pirate Radio Electronics - This document
explores the concepts involved in radio
broadcasting relevant to the pirate radio
operator on VHF FM. This document give a
step by step tour of a typical VHF FM
transmitter system starting with the output
from the tape recorder or mixer, and
finishing with a brief discussion of
aerials.
- Coilless
FM transmitter - The RF oscillator using
the inverter N2 and 10.7Mhz ceramic filter.
Output driver inverters are in parallel the
output impedance will be low so that it can
directly drive an aerial of 1/4th
wavelength. Since the output is square wave
there will be a lot of harmonics in it. The
9th harmonics of 10.7Mhz (96.3Mhz) will
hence be at the center of the FM band.
- 1W
PLL transmitter - Suitable for study
purposes, you can use the RF part easily for
your projects. However, unless you know how
to build a serial data link and connect this
to a PC or a microcontroller, you won't be
able to use the PLL.
- 2W
transmitter - This is claimed to give
mile of range or so on normal FM band
(around 100 MHz). Don't forget that there is
no such thing as free lunch, stability and
spectral purity suck.
- 3W
FM Transmitter - operates between 90 and
110 MHz
- 4
Watt FM Transmitter - This is a small
but quite powerful FM transmitter having
three RF stages incorporating an audio
preamplifier for better modulation. t has an
output power of 4 Watts and works off 12-18
VDC which makes it easily portable.
- Coil-less
FM Transmitter - Very crude transmitter
which uses the 9th harmonics of 10.7Mhz
(96.3Mhz).
- FM
Band Monaural Transmitter - Varactor
diode gives high quality modulation, pdf
file
- FM
Beacon Broadcast Transmitter (88-108 MHz) -
This circuit will transmit a continuous
audio tone on the FM broadcast band (88-108
MHz) which could used for remote control or
security purposes. Circuit draws about 30 mA
from a 6-9 volt battery and can be received
to about 100 yards. A 555 timer is used to
produce the tone (about 600 Hz) which
frequency modulates a Hartley oscillator. A
second JFET transistor buffer stage is used
to isolate the oscillator from the antenna
so that the antenna position and length has
less effect on the frequency.
- FM
Broadcast VCO and Buffer - for 88-108
MHz
- FM
Band Monoaural Transmitter - high
quality monoaural FM transmitter, FET based
oscillator
- FM
Oscillator With BF900 Dual Gate Mosfet -
This is a 100 MHz frequency FM transmitter
circuit designed aroun BG900. Instead of the
BF900, a BF905 or BF907 can be used without
any problems. This circuit uses 15 V DC
power (50 mA) and outputs RF output of
around 55 mVpp to 50 ohm load. This circuit
has a low frequency deviation.
- FM
Stereo Transmiter
- FM
Transmitter - low powered FM
transmitter, includer circuit board and
parts placement picture
- High
Fidelity FM stereo matrix generator circuit -
circuit is for use with mono transmitters to
give out clear stereo output
- Low
Power FM Transmitter - This circuit
operates from 9V battery and transmits FM
signal at frequency range around 90-108 MHz.
This circuit can take microphone or line
level signals for modulation.
- Micro
Power FM Broadcasting Circuits -
accessories to transmitter circuits: audio
limiter, audio mixer, antenna and essential
modifications for Ramsey FM10
- Mighty's
Pirate Radio - many radio circuits,
including mono and stereo FM
transmitters
- Phone
Broadcaster - telephone call FM
transmitter
- Small
Radio Transmitter - information about
building a small radio transmitter, which
has a PCB 1.75" x 2.5" (45mm x 68
mm) and has a range of about 30 yards or so
at 85-108 MHz frequency range. This plan is
based on Velleman kit circuit which is
slightly modified (this article has a new
circuit board design).
- Um
excelente gerador de FM para a faixa de 88 a
108 MHz - PLL syntetized generator of FM
for the band of 88 the 108 MHz, text in
portugese, you can use
- We-man's
radio circuits - FM transmitters, fax
interface and antenna design
- World's
simplest transmitter - Range and
stability is not premium, but it works! Its
a demonstration of what can be done with
little to none resources. This circuit is
based on 74LS13 logic IC!
- Stereo
encoder I A simple FM stereo signal
encoder circuit design that has been has
circulating around for ages. Adding this
circuit to a mono FM transmitter turns it to
a stereo FM transmitter,
- Stereo
encoder II This is a stereo modulator
circuit that can turn a mono FM transmitter
to a stereo FM transmitter. This circuit
have been mentioned to have a bit of noise,
filtering is not sufficient, but otherwise
it can be made to work extremely
nicely.
- World's
simplest FM transmitter schematic If you
cannot assemble this transmitter, then
perhaps you should give up on assembling
anything at all. Range and stability is not
premium, might not meet all signal purity
specifications, but it works! This circuit
is a demonstration of what can be done with
little to none resources. This circuit is
based on 74LS13 TTL IC!
- Simple
small FM transmitter schematic This FM
transmitter gives 200-500 meters of
range.
- FM
Band Monaural Transmitter A high quality
monaura FM transmitter is quite useful in a
variety of applications. The audio from a TV
or entertainment system may be transmitted
for remote or portable listening and for
wireless earphone listening. This is a very
simple FM transmitter with FET based FM
oscillator modulated with varactor
diode.
- FM
Jammer - Here's a quick and simple
project. The Amazing One Transistor FM
Transmitter. It is a redesign of a circuit
sold many years ago by PPG electronics
called the TV Jammer. Though it transmits
only a MONO FM carrier, it can still quite
effectively "Wipe Out" most
stations on a STEREO receiver from about 30
feet away (with the optional antenna).
Mini FM transmitters take place as one of the
standard circuit types in an amateur electronics
fan's beginning steps. When done right, they
provide very clear wireless sound transmission
through an ordinary FM radio over a remarkable
distance Miniature FM transmitters with built-in
microphone are sometimes called bugs. Bugs are
generally used for room monitoring, baby
listening and nature research.Please note that
"BUGS" are illegal in many countries.
- FM
Oscillator - circuit for a VCO and
buffer that operates across the entire FM
broadcast band (88-108 MHz)
- 136kHz
1kW transmitter
- Building
a very simple AM voice transmitter - If
a crystal radio is the distilled essence of
a radio, this transmitter is the matching
distilled essence of transmitters. The
transmitter goes together in about 10
minutes, and is small enough to fit in the
palm of your hand. Depending on the antenna,
the transmitter can send voice and music
across the room, or across the street. The
transmitting frequency of the design is 1
MHz.
- Micropower
AM band radio station - simple
transmitter offers surprisingly good signal
quality, pdf file
- Micro
Power AM Broadcast Transmitter - 74HC14
hex Schmitt trigger inverter is used as a
square wave oscillator to drive a small
signal transistor in a class C amplifier
configuration
- Class
E AM Transmitter Descriptions, Circuits,
Etc. - Class E amplifiers are very
efficient amps and are generally built with
MOSFET transistors. The principle is to
drive the MOSFET's gate input with square
waves to quickly put the device into it's
low ohmic region and to do this when the
voltage across the drain of the MOSFET is at
or near zero volts. This greatly reduces the
heat dissipated by the MOSFET and increases
efficiency. A choke value for the drain is
chosen so that it resonates at the operating
frequency, in combination with the parasitic
capacitance of the drain and the output
filter. The "fly wheel" effect of
the resonant tank causes the drain voltage
to drop to zero before the MOSFET is
switched back on. Efficiencies of 70% or
more can be achieved this way. This article
describes a simple Class E transmitter and
is shown built for 40 meters. It uses a
74HC02 NOR gate as a crystal oscillator. The
amplifier delivers about 2 watts output with
a 9 volt supply and about 4 watts with a 12
volt supply.
- The
Grenade Transmitter - This is shortwave
transmitter based on The Animal's infamous
"Grenade" design. It operared at
12-14V power and outputs up to 10W AM
transmission at 40 meter frequency area
(6000-8000 Kilohertz). This design uses
crystal to define the transmitting frequency
and has limiter/compressor in the audio
input.
- 2400MHz
Signal Source - This unit is an attempt
to make the simplest possible signal source
for 13cm without the usual grief of not
finishing up on the right frequency. The
oscillator starts with a readily available
96MHz crystal and multiplying this by 25
goes up to 2400MHz. The use of filters takes
the guesswork out of finding the correct
frequencies. The output is -10dBm (100
microwatts).
- 2.4
GHz FM ATV - a project concept - This
article describes how to modify consumer
wireless video link devices for ATV use.
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