Friday, July 4, 2014

A Transmitter Circuits

1 Valve 3.5MH CW Transmitters

1 Valve CW Transmitter

1.5 Volt Tracking Transmitter

1.5 Volt Tracking Transmitter 2

10W HF Linear Amplifier

150mW FM Transmitter

1W CW Transmitter

2 Transistor FM Transmitters

2 Transistor FM Transmitters:

2 Valve 40m CW Transmitter

2 Valve CW Transmitter

20M, 4W QRP Transmitter

250mW HF CW Transmitter

27MHz AM/CW Transmitter

2N2222 40 Meter CW / DSB Tranceiver

3 Watt FM Transmitter

30 Meter QRP Transmitter for Morse Code

3W HF QRP Linear Amplifier

4 Transistor Tracking Transmitter

4 Transistor Transmitter

433MHz Transmitter using SAW Resonator

5 Watt HF CW Transmitter

500mW HF Linear Amplifier

56K RF Modem

5W PLL Transmitter

7Mhz AM/CW Amateur Radio Transmitter

7MHz QRP Transmitter

7MHz SSB Transceiver:  Circuit digram and brief description of 7MHz SSB Transceiver for Hams. The circuit is designed around two numbers of MC1496. It can push around 80 Watts with IRF840 in the final. You can down load HTML version or the printer friendly word document.

80 Meter DSB Transmitter

807 and 1625 Valves:  data on vacuum tubes 807 and 1625 used in ham radio transmitters. Describes various pin voltages and different operation modes.

AM DSB Transmitter for Hams:  circuit diagram of simple double side band suppressed carrier (DSBSC) transmitter for hams. Circuit uses crystal oscillator, crystal can be switched for multi band operation. .

AM oscillator for Wireless Microphones

AM Transmitter

Antennas for Ham Transmitters:  Describes how to construct various type of antenna for Ham Radio Transmitters.

AT Volt Repeater Controllers

Basic FM Radio Transmitters

Basic RF Oscillator #1

Basic RF Transmitter for PIR Sensors

Battery operated FM rebroadcast transmitter :  Gives you 10 to 20 meters range and runs for months on a single penlight cell.

Ceramic Filter BFO:  Receive SSB and CW transmissions on your BC receiver. Simple BFO is build around 455 KHz Ceramic Filter.

Crystal Controlled FM Transmitter

Current Transmitter With Linear Voltage Transfer Rejects Ground Noise:  08/07/00 Electronic Design - Ideas for Design / Many systems use current signals to control remote instruments. The advantage of this method is the ability to operate with two remotely connected power supplies even if their grounds are not the same. In these cases, it's necessary for the output. . .

Design of Brookdale AT Volt Repeater System Exciter:  uses a pair of Hamtronics model TA4512-watt narrow-band FM voice transmitters to develop video and audio carriers on439.250 MHz and443.750 MHz

Easy 2 Meter Transmitter:  This project is a simple transmitter using only one crystal and will cover 145.00 to 146.00 MHz. The crystal is a 44.9333 MHz crystal for 145.500 receive, as used in the Trio (Kenwood) 2200, PYE, Motorolla, Tait equipment, to name but four. The frequency of the crystal is not critical as almost any other xtal for the 2-meter band will function

Experimental Data Transmitter for Fiber optics

Fibroptic transmitter

FM Band Monaural Transmitter

FM Beacon 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 about30 mA from a 6-9 volt battery and can be received to about100 yards.

FM Broadcast Audio Transmitter :  Monophonic FM band transmitter for home use.

FM Bug

FM Radio Bug

FM Radio Telephone Transmitter

FM Radio Transmitter

FM Radio Transmitter #1

FM Radio Transmitters With OpAmp

FM Transmitter

FM transmitter

Four Channel Wireless Transmitter & Receiver:

Four Transistor Tracking Transmitter

Frequency Agile 80m CW QRP Transmitter

High Power FM Bug

Infra / Radio Remote Control Transmitter / Receiver

Infrared Transmitter and Receiver Schematic Diagrams

Infrared Transmitter Circuit:

Infrared Transmitter for Audio:  (Amplitude Modulated IR)

Laser Diode Transmitter

Laser Transmitter Schematics

Light Sensing RF Transmitter

Li'l 7 AM Transmitter Schematic

Long Range FM Transmitter

Low Power FM Transmitter

Micro Power AM Broadcast Transmitters:  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.

Micro Spy With FETs

Micro Spy With TTL

Micro Spy With USW

MicroPower FM Broadcasting Circuits

Miniature FM Transmitter #2

Miniature FM Transmitter #3

Miniature FM Transmitter #4

Miniature FM Transmitters #4

Miniature MW Transmitter:  circuit diagram of simple medium wave transmitter using BF494B. This simple transmitter have a range of 200 meters. .

MINIATURE TRANSMITTER:   What can I say about this circuit except brilliant I have actually built this one and was very impressed, I built it using leaded components maybe one day try a bit of smd make it even smaller, problems needs a big Ariel to transmit over any great distance.

One Valve 3.5MH CW Transmitter

Op Amp Based FM Transmitter

Phasing SSB Exciter

QRP HF Transmitter

QRP Keyer:  very simple keyer circuit using only one transistor.

QRP SSB Transmitter

Quality FM Transmitter

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Sensitive FM Transmitter

Shortwave Radio Transmitter

Shortwave Transmitter:

Simple FM Microphone

Simple FM Transmitter #1

Simple Low FER Transmitter

Simple RF Transmitter

Simple T Volt Transmitter #1

Simple T Volt Transmitter #2

Simplest RF Transmitter

Small circuit forms programmable 4 to 20 mtransmitter:  04/17/03  EDN-Design Ideas / One of the key challenges in the design of 4 to 20-mA current transmitters is the voltage-to-current conversion stage. Conventional transmitters use multiple op amps and transistors to perform the conversion function. These approaches have been around for a long time, but they are usually inflexible, have poor power efficiency, and have limited current compliance...

Small FM Transmitter #2

Small Radio Transmitter

Spark gap Transmitter

Surveillance Transmitter Detector:  This circuit can be used to "sweep" an area or room and will indicate if a surveillance device is operative. The problem in making a suitable a detector is to get its sensitivity just right, Too much sensitivity and it will respond to radio broadcasts, too little, and nothing will be heard.

T Volt Transmitter:  allows you to send video to any television in the house, Poptronix kit circuit

Telephone Transmitter

Three Watt FM Transmitters

Tracking Transmitter #1

Tracking Transmitter #2

Transmitter senses triple relative humidity figures:  09/26/2002  EDN - Design Ideas / The circuit in Figure 1 is a triple, relative-humidity sensor and radio transmitter. Sensors 1 and 2 form two gated oscillators with natural frequencies of 10 and 5 kHz, respectively, at relative humidity of 50%. The gated oscillators use variable resistances R2 and R3, respectively. Together, these two oscillators generate FSK-modulated outputs at output of IC1B, Pin 6..

Transmitter using LM317:

Two Transistor FM Transmitters

Two Valve 40m CW Transmitter

VHF / UHF T Volt Modulator:   Elektor January1985

VHF Audio Video Transmitter:  This circuit is a TV transmitter on VHF band.

VHF beacon transmitter

VHF FM Transmitter

VHF Transmitter

Video / Audio Wireless Transmitter:  circuit diagram and project description

Video to RF Modulator:  This circuit is a RF modulator which can be used for modeling of video signal.

Video/Audio Wireless Transmitter

Wire Tracer

Wireless IR headphone Transmitter

Wireless Microphone #1

Wireless Microphone #2

Wireless Microphone #3

Wireless Microphone Transmitter

WLW 500KW Transmitter Schematic

XTAL Locked tone Transmitter

detailsUSB FM Transmitter Circuit for PC and Laptop



Here's a small FM transmitter ciruit for your desktop or laptop to enjoy the movie and music from a distance. This FM transmitter, which is powered by USB, recovers output on your computer or your MP3 player to the relay on the tape FM (frequency 108 MHz). For Assemblying this FM transmitter kit, an electronics hobbyist will have built in about 30 minutes.

FM Transmitter Construction
It is not necessary to drill the transmitter PCB. All components will be soldered to the plate with their legs folded.

The two transistors and the LEDs are polarized:
The transistor has a flat side, the LED a foot longer than the other is the anode (A), the other is the cathode (K). The audio cable (minijack) must be transformed from a stereo cable into a cable.
Mono Sound:
Soldering together the white and red cables, leaving aside the yellow cable (mass). The frequency setting will be turning the variable capacitor gently with a screwdriver or thin cardboard but rigid.

FM Transmitter Parts List
* 1 Ohm resistor 510 (green - brown - brown)
* 100 resistor 1 kOhm (brown - black - yellow)
* 1 MOhm resistors (brown - black - green)
* 1 capacitor 0.1 uF (0.1)
* 1 nF capacitor 47 (0.047)
* 1 capacitor 4.7 pF (479)
* 2 pF capacitors 22 (22)
* 1 variable capacitor 1.5 pF ... 15
* 2 transistor BF 246 (F246A)
* 1 red LED
* 1 audio cable (minijack)

Wednesday, July 2, 2014

The Complete FM Bug



FM BUG Circuit

Corporate espionage is reaching new heights in sophistication. The latest information to be released shows the depths firms will go to pry into a rival firm's operations.
By using the latest in electronic bugging, they have stolen information, secrets and even formulas known only to the inventors themselves.
Take the example of one firm:Leaks from Top Management level remained a mystery until, one day, a bug was discovered inside the Managing Director's office.Sitting prominently on his desk was a gift box of imported cigars!Cleverly concealed in the lower part of the box was a miniature FM transmitter . . all a gift from a phony sales rep.This is just one of the many bugging devices available on the eaves-dropping market. The range includes pen and pencil holders, trophies, framed pictures and office furniture with false bottom drawers.
These products are readily sold to fledgling companies, eager to nestle into big brother's market.
And for a while these bugging devices worked. Few firms knew of their existence, and even less on how to sniff them out.
But that has all changed now. If a corporation suspects a leak at any level, the first thing they order is an investigation into security. Not only personnel, but information and electronic security.
Debugging has grown into big business. Most large security organisations have a section concentrating on electronic surveillance including bugging and debugging.
They use scanners to detect hidden devices and can locate absolutely anything, anywhere, and on any frequency.
It was only after the firm above had commissioned a scan of the entire floor, that the cigar box was discovered. Its innocence had deceived everyone. And cost them a small fortune!
Bugging of this kind is completely illegal and we don't subscribe to this type of application at all.
But the uses for our SUPER-SNOOP FM WIRELESS MICROPHONE can be harmless, helpful and a lot of fun.
Our unit is both compact and very sensitive and can be used to pick up even the faintest of conversations or noises and transmit them 20 or so metres to any FM receiver.
When you build the FM BUG you will see why we consider the design to be very clever. We have used only low priced components and they are all easy to obtain.
No air trimmer capacitor is required as the coil is squeezed slightly to obtain the desired frequency. This has allowed us to fit the bug into a tooth-brush case so that it can be carried around or placed on a shelf.
If it is set between two books it will be hidden from view or as a supervision accessory it can be placed on a small child, etc. The transmitted signal will over-ride the background noise and the output will be clean. If the child wanders beyond the range of the transmitter, the background noise will come up and signal that the tot is out of range.
As an added bonus, you can listen to the chatterings and squabbles as the children amuse themselves in the back yard.
It is also great for picking up the first signs of a child awakening from his afternoon sleep or it can be used as an indicator from a bed-ridden patient.
The great advantage of the bug is the absence of wires. And since it draws only about 5-10 milliamps, the pair of AAA cells will last for many months.
The success of this FM BUG is the use of TWO transistors in the circuit. To create a good design, like this, each transistor should be required to perform only one task. In any type of transmitter, there is a minimum of two tasks.
One is to amplify the signal from the microphone and the other is to provide a high frequency oscillator.
The amplified microphone signal is injected into the oscillator to modify its frequency and thus produce a FREQUENCY MODULATED oscillator. If an aerial is connected to the output of the oscillator, some of the energy will be radiated into the atmosphere.
To increase the output of our design, an RF amplifier would be needed but this gets into legal technicalities with maximum transmitting power.
It may be of Interest to know that a record distance of 310 miles was achieved with a 350 micro-watt transmitter in the USA, some 15 years ago. This equates to an astounding ONE MILLION miles per watt!
In simple terms, an RF amplifier becomes a LINEAR amplifier.
We have opted for sensitivity and the first transistor is employed as a pre-amplifier. This will enable you to pick up very low-level sounds and transmit them about 20 to 50 metres.
The only critical component in the FM BUG is the oscillator coil. When I say critical, I am referring to its effect on the frequency. Its critical nature only means it must not be touched when the transmitter is in operation as this will detune the circuit completely.
It is the only component which needs to be adjusted or aligned and we will cover its winding and formation in detail.
The oscillator coil is made out of tinned copper wire and does not need any insulation. This is not normal practice but since the coil is small and rigid, the turns are unable to touch each other and short-out.
The coil is made by winding the tinned copper wire over a medium-size Philips screw-driver. The gauge of wire, the diameter of the coil and the spacing between turns is not extremely important and it will be adjusted in the alignment stage. However when the project is fully aligned, it must not be touched at all.
Don't be over-worried at this stage. Just follow the size and shape as shown in the diagram and everything will come out right in the end.

The coil has 5 turns and is wound on a 3.5mm shaft. To be more specific, it has 5 loops of wire at the top and each end terminates at the PC board. The coil must be wound in a clock-wise direction to fit onto the board and if you make a mistake, rewind the coil in the opposite direction.
Construction is quite straight-forward as everything is mounted on the printed circuit board. The only point to watch is the height of some of the components. The electrolytic must be folded over so that the board will fit into the case.
Positioning of the parts is not as critical as you think as the final frequency is adjusted by squeezing the coil together or stretching it apart.
However it is important to keep the component leads as short as possible and the soldering neat due to the high frequencies involved. The components must be soldered firmly to the board so that they do not move when the transmitter is being carried.
Even the poorest of soldering will work but who wants to see poor soldering on a project?
The soldering may not affect the resulting frequency but poor layout of the components certainly will.
All the resistors must be pressed firmly against the PC board before soldering and the two transistors must be pushed so that they are as closes as possible to the board.
Some BC 547 transistors will not work in the circuit. Maybe the frequency is too high. SGS BC 547 transistors did not work at all. The other two types: f BC 547 and Philips BC 547 worked perfectly.
All the small-value capacitors are ceramic as they are not critical in value and do not need to be high stability. But you must be careful when identifying them. It would be a very simple mistake to buy a 56p instead of 5p6 because there is no difference in the size. 22n may be identified with 223 or 22n or .022. A capacitor marked 22k will be a 22p cap and will not be suitable. The 1n capacitor may be marked 1n or .001 or 102. These are all the same value. The value 101 or 103 is NOT 1n so be careful, the caps may be about the same size. The rule is: don't use a capacitor unless its markings are clear and you are sure of the value.

The complete FM BUG

The switch is mounted on the PC board with its three terminals fitted into the large holes.
The final items to add to the board are the two AAA cells. These come with the kit and we have chosen them for slenderness so that they can be fitted side-by-side.
It is very difficult to solder to the zinc case but if you roughen the surface with a file and use a large, HOT, soldering iron, the job can be done very quickly. Use a piece of tinned copper wire to join the positive of one to the negative of the other. At the other end, solder longer lengths of wire so that they can be connected directly to the PC board. Make sure the positive terminal connects to the plus on the PC board.

Top and bottom of the FM BUG PC board

AAA cells are also obtainable at photographic shops. The only alternative is an 'N' cell which is nearly as thin as an AAA cell but only half the length.
The terminal marked A on the board is the antenna output. For a frequency of 90MHz, the antenna should be 165cm long. This is classified as a half-wave antenna and provides one of the most effective radiators. If you find the antenna gets in the way you can opt for a quarter-wave antenna and this will be 83cm long. If you only require to transmit 10 to 20 metres the antenna can be as short as 42cm or even as low as 5 or 10 cm.
The most suitable length will depend on the sensitivity of the FM radio used to pick up the signal and the obstructions between the transmitter and receiver. It will be a good experiment for you to 'cut' your own antenna and determine which is the most suitable for your application.
The circuit consists of two separate stages. The first is an audio pre-amplifier and the second is a 90MHz oscillator.
The first stage is very simple to explain. It is a self-biasing common-emitter amplifier capable of amplifying minute signals picked up by the electret microphone. It delivers these to the oscillator stage. The amplification of the first stage is about 70 and it only operates at audio frequencies. The 22n capacitor isolates the microphone from the base voltage of the transistor and allows only AC signals to pass through. The transistor is automatically biased via the 1M resistor which is fed from the voltage appearing at the collector. This is a simple yet very effective circuit. The output from the transistor passes through a 2.2u electrolytic. This value is not critical as its sole purpose is to couple the two stages.
The 47k, 1n, 470R and 22n components are not critical either. So, what are the critical components in this circuit?
The critical components are the coil and 47p capacitor. These determine the frequency at which the bug will transmit. In addition, the effective capacitance of the transistor plays a deciding factor in the resulting frequency.
This stage is basically a free-running 90MHz oscillator in which the feedback path is the 5p6 capacitor.
When the circuit is turned on, a pulse of electricity passes through the collector-emitter circuit and this also includes the parallel tuned circuit made up of the oscillator coil and the 47p capacitor. This pulse of electricity is due to the transistor being turned on via the 47k resistor in the base circuit.
When ever energy is injected into a tuned circuit, the energy is firstly absorbed by the capacitor. The electricity will then flow out to the coil where it is converted to magnetic flux. The magnetic flux will cut the turns of wire in the coil and produce current and voltage which will be passed to the capacitor.
In theory, this current will flow back and forth indefinitely, however in practice, there are a number of losses which will cause the oscillations to die down fairly quickly.
If a feedback circuit is provided for the stage, the natural RESONANT frequency of the coil/capacitor combination will be maintained. The 5p6 provides this feedback path and keeps the transistor oscillating.
The 5p6 feeds a small sample of the voltage appearing at the collector, to the emitter and modifies the emitter voltage. The transistor sees its base-to-emitter voltage altering in harmony with the resonant frequency of the tuned circuit and turns the collector on and off at the same frequency.
Thus there is a degree of stability in the oscillator frequency.
The actual frequency of the stage is dependent upon the total capacitance of the circuit and this includes all the other components to a minor extent.
Once the basic frequency of 90MHz is set, the variations in frequency are produced by the changes in effective capacitance of the transistor. This occurs when its base voltage is increased and reduced. The electret microphone picks up the sound waves which are amplified by the first transistor and the resulting frequency is passed to the base of Q2 via the 2.2u electrolytic.
This alters the gain of the transistor and changes its internal capacitance. This junction capacitance modifies the oscillator with a frequency equal to the sound entering the microphone thus FREQUENCY MODULATING the circuit. A short length of antenna wire is connected to the collector of the oscillator via a coupling capacitor and some of the energy of the circuit will be radiated to the surroundings.
Any FM receiver will pick up this energy and decode the audio portion of the signal.
When the FM BUG is complete, checked and ready for insertion into its case, there is one slight adjustment which must be made to align it to the correct frequency.
As we have said, the only critical component is the oscillator coil. It is the only item which is adjustable.
Since we are working with a very high frequency, the proximity of your hand or even a metal screw-driver will tend to de-tune the oscillator appreciably.
For this reason you must use a plastic aligning stick to make the adjustment. Any piece of plastic will do. A knitting needle, pen barrel or plastic stirring stick can be used.
Place the bug about a metre from the FM radio and switch both units on. Tune the radio to an unused portion of the band and use the alignment stick to push the turns of the coil together. Make sure none of the turns touch each other as this will short out the operation of the oscillator.
All of a sudden you will hear the background noise diminish and you may even get feed back. This amount of adjustment is sufficient. Place the BUG in its case and tape up the two halves.
The fine tuning between radio and transmitter is done on the radio. Peak the reception and move the BUG further away. Peak the fine tune again and move the BUG into another part of the house and see how far it will transmit.
If the bug fails to operate, you have a problem. Simple digital tests will not fix it nor will ordinary audio procedures. The frequency at which the BUG operates is too high.
You have to use a new method called comparison.
This involves the comparing of a unit which works, with the faulty unit.
This means it is ideal for a group of constructors to build a number of units and compare one against the other.
This will not be possible with individual constructors and they will have to adapt this fault-finding section.
The first fact you have to establish is the correct operation of the FM receiver.
If you have another BUG and it is capable of transmitting through the radio you know the radio is tuned to the correct frequency. Otherwise you will have to double-check the tuning of the dial and make sure the radio is switched to the correct setting.
The next stage is to determine if the BUG is functioning AT ALL. The only voltage measurements you can make are across the collector-emitter terminals of the first transistor (1 v to 1.5v) and across the collector-emitter terminals of the second transistor (1.3v to 1.5v) These values won't tell you much, except that the battery voltage is reaching the component.
Tune the radio to about 90MHz and lay the radio antenna very close to the antenna of the BUG. Switch the BUG on and off via the slide switch. You should hear a click in the radio if the BUG is on a frequency NEAR 90MHz. Move the turns of the aerial coil together or apart with a plastic stick as you switch the unit ON and OFF.
If a click is heard but no feed-back, the oscillator will be operating but not the pre-amp stage. This could be due to the electret microphone being around the wrong way, the transistor around the wrong way, a missing component or an open 2.2u electro.
If the fault cannot be located, compare your unit with a friend's. You may have made a solder bridge, connected the batteries around the wrong way, made the coil too big or used the wrong value capacitor for one of the values.
If all this fails, put the unit aside and start again.

1 - 470R
1 - 10k
1 - 22k
1 - 47k
1 - 1M
1 - 5.6p ceramic = 5p6
1 - 22p ceramic or 27p or 33p
1 - 47p ceramic
1 - 1n ceramic = 1,000p or 102
1 - 22n ceramic = .022 or 223
1 - 2.2u 16v or 25v
2 - BC 547 transistors
1 - mini slide switch spdt.
1 - electret microphone (insert)
2 - AAA cells
10cm tinned copper wire
2 - metres aerial wire
1 - FM BUG PC board