Long range AM transmitter Circuit Schematic With Explnation

This is a long range transmitter.This circuit can send signals up to 2km.So that you have to use 1m copper wire.The power of this transmitter has been increased by usin two transistors. When you use this transmitter do give power with out connecting the antenna.Because it will burn your transistors.






Note


# The transformer T1 can be a general purpose audio driver transformer seen in transistor radios.

# The inductor L1 can be made by making 56 turns of 365 WG enameled copper wire on a 1 cm former.

# Inductor L2 can be a 10 mH general purpose radio frequency choke.

# The circuit can be powered from a 9V PP3 battery.

5 to 500 feet transmitter Circuit Schematic With Explnation

This is so useful circuit because this circuit can transmit signals 5 feet to 500 feet.Here I have used common transistor 2N5225 If you are unable to find this you can use any general purpose transistor.



Note

# About L1 is mentioned on the picture

# This circuit operates with 9V DC

# use 5cm wire as an antenna

Parts and schematic for an AM radio transmitter

Small components needed to build an AM radio transmitter :

- 555 timer chip
- NPN transistor
- two #103 capacitors (0.01 microfarads or 10,000 picofarads)
- #102 capacitor (0.001 microfarads or 1,000 picofarads)
- some short wires
- two 1 Kilohm resistors
- 10 Kilohm resistor
- 1/8 inch (3.5 millimeter) female audio jack (yours may have more or less than three
wires, but it must have at least two)
- 5 Kilohm potentiometer

Bigger Stuff:
- 1/8 inch (3.5 millimeter) male audio cable
- AM radio receiver
- Antenna. Yours doesn't have to be made out of a pop can, but the pop can works
- Breadboard
Schematic :

S:www.instructables.com

a very simple AM voice transmitter construction

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.

I put together my first version with simple clip leads (no soldering, no printed circuit board, not even a battery clip). This version is much sturdier and convenient.

S:sci-toys.com

74HC240 Qrp Transmitter.

Description.

The ARRL HB describes an experimental 0.5W transmitter that uses a 74HC240 octal inverting buffer. One section is used as a fundamental frequency oscillator, four sections are used as an amplifier, while three sections are grounded, and unused. The three unused sections can be put to use in further expansion into a TCVR. Q1 is used to key the transmitter, while the 7808 provides a stable 8V DC supply. THe IC will dissipate heat, and a heat sink should be glued onto it using epoxy. The low pass filter is standard, and the values for some HF bands are given in the table above. This design forms the basis of a minimal QRP TCVR that I am developing, as part of my education in electronics.

http://www.qsl.net/5z4ft/74hc240qrp.html

1W AM Transmitter circuit and explanation

This AM transmitter circuit provides a nice, clean output of about 1 Watt (carrier power). Though designed for the medium wave band (circa 1.5 MHz) it would work equally well on higher frequencies (6.2 MHz for example) with a few tweaks in component values (see table on left - C15 should be adjusted for maximum output).

The carrier (produced by the 4049) is modulated at low-level by the MC1496 balanced modulator. There are then a couple of stages of linear amplification to reach the final output power so no modulation transformer is required. TR2, TR5 and TR6 are BC108 or similar; TR3 is a 2N3053 or 2N4427 or 2N3866 or any low/medium power NPN transistor. The main output transistors, TR4 and TR5 were originally 2SC1162 but BD135 or BD139 or other medium power RF transistors will do equally well. T1 uses a pre-tuned TOKO KANK3334 coil, the other transformers are wound on the red T50-2 toroids (the number of turns shown is the ratio, use about 4 to 5 times that number in reality - less at higher frequencies). The LED lights up if current in the output amplifier goes too high, so it's a kind of 'high SWR' warning.

Source: ZFM

ZN414 Portable AM Receiver circuit and description

Notes:
Designed around the popular ZN414 ic this receiver covers the AM band from 550 - 1600 KHz with the values shown. For Longwave the coil needs to be changed. Use one from an old MW radio to save time. The ZN414 is a tuned radio frequency designed and incorporates several RF stages and an AM detector. It is easily overloaded and the operating voltage is critical to achieve good results.

The BC107 acts as a voltage follower, the four 1N4148 diodes providing a stable 2.4V supply. With the 10k pot , which acts as a selectivity control, and the b-e voltage drop of the BC107, the operating voltage for the ZN414 is variable from 0 to 1.8volts DC. If you live in an area that is permeated with strong radio signals, then the voltage will need to be decreased. I found optimum performance with a supply of around 1.2 volts.

Circuit diagram

The audio amplifier is built around an inverting 741 op-amp. Extra current boost is provided using the BC109 / BC179 complementary transistor pair. The voltage gain of the complete audio amplifier is around 15. The audio output of the complete receiver is really quite good and free from distortion. I may provide some sound samples later..

author: Andy Collinson
e-mail:
web site: http://www.zen22142.zen.co.uk

Audio Processor for AM Transmitter This audio circuit is used for AM transmitter audio procesing. It equipped with low pass filter circuit for AM spe

This audio circuit is used for AM transmitter audio procesing. It equipped with low pass filter circuit for AM spectrum. It's easy for use.

MK1 AM Audio Processor
My first attempt at an improved audio processor for GCR using a Plessey SL-6270 VOGAD (VOice controlled Gain Adjusting Device) which is designed more for PMR use than broadcast use but with the right parameters does a reasonable job. It deals with a massive dynamic range of inputs (about 60dB) which does tend to mean that if you don't set it up properly you can hear every tiny background noise in the studio. There's a bit of low and high-pass filtering on the input to avoid unwanted frequencies causing the compressor to 'pump'. There's also a lovely 7-pole Chebyshev low-pass filter on the output with a cut-off at about 6 kHz. All the op-amps are TL072 or TL074. Watch out for the difference between the 'earth' symbol and the 'ground' symbol as one relates to 0V and the other to mid-rail (typical supply voltage is 15V).

MK 2 AM Audio Processor
The Mark 2 version of the processor above. Now with an added limiter after the compressor (based around an MC3340 and a rather odd BSV71/BFR29 I.G.F.E.T.). A new 6-pole output low-pass filter to provide a tight fit to the transmitter specifications allowed at the time for closed-loop AM radio stations. There's a bit more HF boost (or pre-emphasis) before the clipper on this version to give the audio a more 'lively' feel. This design was in use at GCR for about 2 years until my super 3-band processor took over. Same precautions over the diagram as above apply and op-amps are also TL072 or TL072.


MK 3 AM Audio Processor (Part I)
The Mark 3 version got massively more sophisticated (and better sounding). This diagram is for the heart of the processor. It's a 3 band audio processor/limiter/compressor (call it what you will) with a few special features: (1) The decay on the bass compressor is tied in to the mid compressor which gives a much more balanced sound, and (2) there are cross-overs before and after each compressor, thereby reducing any distortion produced. The resulting sound is very loud and very impressive. The 3 audio bands compressed are 0-250 Hz, 250-1300 Hz and 1300-6500 Hz. The +/- 8V supply is quite critical as it sets the threshold for compression to the MC3340 chips. There's still a transmitter kicking around with this processor in it - if I can get my hands on it I'll record some output.


MK 3 AM Audio Processor (Part II)
This is the second half of the Mark 3 diagram and shows the input high and low-pass filtering; the clipper (with a snazzy LED to show when clipping is occuring); and a new and even better output 6.5 kHz low-pass filter together with a phase corrector to provide overshoot compensation (and therefore allow the transmitter to be driven harder).




AM Low Pass Filter Response
The frequency response of the output filter is flat to 6 kHz, -3dB @ 6.5 kHz, -23dB @ 7.6 kHz and -40dB @ 9 kHz, which fits exactly the allowed response for closed-loop AM stations for which it was designed. Without the overshoot compensator, the filter has an overshoot of around 2.6 dB; with it, overshoot is virtually nothing - thereby giving a 2.6 dB increase in loudness. All components (including the capacitors) need to be 1% tolerance for this circuit to work properly.

Source: ZFM

500 KHz to 1600 KHz AM Transmitter Circuit

500 KHz to 1600 KHz AM Transmitter Circuit

The circuit is in two half, an audio amplifier and an RF oscillator. The oscillator is built around Q1 and associated components. The tank circuit L1 and VC1 is tunable from about 500 KHz to 1600 KHz. These components can be used from an old MW radio, if available. Q1 needs regenerative feedback to oscillate and this is achieved by connecting the base and collector of Q1 to opposite ends of the tank circuit. The 1nF capacitor C7, couples signals from the base to the top of L1, and C2, 100pF ensures that the oscillation is passed from collector, to the emitter, and via the internal base emitter resistance of the transistor, back to the base again. Resistor R2 has an important role in this circuit. It ensures that the oscillation will not be shunted to ground via the very low internal emitter resistance, re of Q1, and also increases the input impedance so that the modulation signal will not be shunted. Oscillation frequency is adjusted with VC1.

The Q2 is wired as a common emitter amplifier, C5 decoupling the emitter resistor and realizing full gain of this stage. The microphone is an electret condenser mic and the amount of AM modulation is adjusted with the 4.7k preset resistor P1. An antenna is not needed, but 30cm of wire may be used at the collector to increase transmitter range.

Thanks To: http://freeelectricalsandtools.blogspot.com/

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Double Side Band AM Transmitter Circuit

The circuit of AM transmitter is designed to transmit (amplitude modulated) DSB (double side band) signals. A modulated AM signal consists of a carrier and two symetrically spaced side bands. The two side bands have the same amplitude and carry the same information. In fact, the carrier itself coveys or carries no information. In a 100% modulated AM signal 2/3 rd of the power is wasted in the carrier and only 1/6th of the power is contained in each side band.

In this transmitter we remove the carrier and transmitt only the two side bands. The effective output of the circuit is three times that of an equivalent AM transmitter.

Op Amp IC741 is used here as a microphone amplifier to amplify the voice picked up by the condenser microphone. The output of the op amp is fed to the double balanced modulator (DBM) build around four IN4148 diodes. The modulation level can be adjusted with the help of preset VR1.

The carrier is generated using crystal oscillator wired around BC548 transistor T2. The carrier is further amplified by transistor T1, which also acts as a buffer between carrier oscillator and the balanced modulator. The working frequency of the transmitter can be changed by using crystals of different frequencies. For multi frequency operation, selection of different crystals can be made using a selector switch.

Ths output of the DBM contains only the product (of audio and carrier) frequencies. The DBM suppresses both the input signals and produces double side band suppressed carrier (DSBSC) at its output. However, since the diodes used in the balanced modulator are not fully matched, the output of the DBM does contain some residual carrier. This is known as carrier leakage. By adjusting the 100 ohm preset VR2 and trimmer C7 you can null the carrier leakage.

To receive DSB signals you need a beat frequency oscillator to reinsert the missing carrier. If you don’t have a beat frequency oscillator, or want to transmitt only AM signal, adjust preset VR2 to leak some carrier so that you can receive the signals on any ordinary radio receiver. In AM mode 100% modulation can be attained by adjusting preset VR1 and VR2.

The DSBSC signal available at the output of the balanced modulator is amplified by two stages of RF linear amplifiers. Transistor 2N2222A (T3) is used as an RF pre amplifier, which provides enough signal amplification to drive the final power amplifier build around transistor SL100B. The output of the final power amplifier is connected to the antenna.

All coils are to be wound ferrite balun core (same as used in TV balun transformer of size 1.4 cm * 0.6 cm) using 24 swg enameled copper wire. Proper heat sink should be provided for SL100B transistor used as final power amplifier.

X1 – 8+8 Turns Bifalar 24 SWG On TV Balune Core
X2 – Primary 12 Turns, Secondary 4 Turns. 24 SWG on TV Balun Core (dot indicates start of coil).
X3 – 20 Turns 24 SWG on TV Balun Core

Range of the circuit depends on the type of antenna used. It is very important to use matched antenna to radiate the signals effectively. I used horizontal dipole antenna, which is simple and easy to construct. For 7 MHz, ie 40 meter ham band the length of dipole antenna will be 20 meter. Use 75 Ohms co-axial cable to connect antenna and transmitter. I was able to get 57 report from station 80 kilometer away. You can easily add a Linear RF amplifier using IRF830 to get more power.

Micro Power AM Broadcast Transmitter Schematic

Micro Power AM Broadcast Transmitter

In this circuit, a 74HC14 hex Schmitt trigger inverter is used as a square wave oscillator to drive a small signal transistor in a class C amplifier configuration. The oscillator frequency can be either fixed by a crystal or made adjustable (VFO) with a capacitor/resistor combination. A 100pF capacitor is used in place of the crystal for VFO operation. Amplitude modulation is accomplished with a second transistor that controls the DC voltage to the output stage. The modulator stage is biased so that half the supply voltage or 6 volts is applied to the output stage with no modulation. The output stage is tuned and matched to the antenna with a standard variable 30-365 pF capacitor. Approximately 20 milliamps of current will flow in the antenna lead (at frequencies near the top of the band) when the output stage is optimally tuned to the oscillator frequency. A small ‘grain of wheat’ lamp is used to indicate antenna current and optimum settings. The 140 uH inductor was made using a 2 inch length of 7/8 inch (OD) PVC pipe wound with 120 turns of #28 copper wire. Best performance is obtained near the high end of the broadcast band (1.6 MHz) since the antenna length is only a very small fraction of a wavelength. Input power to the amplifier is less than 100 milliwatts and antenna length is 3 meters or less which complies with FCC rules. Output power is somewhere in the 40 microwatt range and the signal can be heard approximately 80 feet. Radiated power output can be approximated by working out the antenna radiation resistance and multiplying by the antenna current squared. The radiation resistance for a dipole antenna less than 1/4 wavelength is

R = 80*[(pi)^2]*[(Length/wavelength)^2]*(a factor depending on the form of the current distribution) The factor depending on the current distribution turns out to be [(average current along the rod)/(feed current)]^2 for short rods, which is 1/4 for a linearly-tapered current distribution falling to zero at the ends. Even if the rods are capped with plates, this factor cannot be larger than 1. Substituting values for a 9.8 foot dipole at a frequency of 1.6 MHz we get R= 790*.000354*.25 = .07 Ohms. And the resistance will be only half as much for a monopole or 0.035 Ohms. Radiated power at 20 milliamps works out to about I^2 * R = 14 microwatts.

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