FM Bug Transmitter V5
3
3 Transmitter FM Bug Transmitter The Best FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike. I do however, receive many requests for a higher powered circuit and better microphone sensitivity. Now I can introduce the new FM Wireless Microphone (v5), which also has a better frequency stability, over 1Km range (under ideal conditions) and is good on microphone sensitivity and eliminates the nightmare of a beginner THERE IS NO WOUND COIL!! it is the part of the PCB itself. This has been achieved by adding an RF amplifier buffer (with 10dB gain) and an AF preamplifier to boost the modulation a little. This power is enough to receive the signals through a regular Sony/Aiwa Walkman radio, which is the best recourse to pretend you are enjoying music!, when you are required to monitor from a public place. The most critical component , from sensitivity aspect is the Condenser Microphone. In the early stage of this project, I used the "normal" mic used in TapeRecorder, which costed me just Rs 5, leading me to a rather disappointing project.The response of the circuit to feeble sounds, which we are interested in , was terrible.I used to speak "IN TO" the mic as if addressing a meeting. Then , I got the special High Sensitive Mic used in Cordless Phone's Base unit from a local electronic component store. This opened a new world and it can even transmits sounds which no one can even hear, at the eavesdropping site. The Mic should be directly exposed to the surrounding , may be through a slit in the enclosure, exposing just the "Front face" of the mic on the surface. The Mic dose not require to be directed to the source of the sound for it can receive the reflected waves from the wall, if present. But there should be no obstacle in the line of the Mic, at least 2 feet away, so that it can receive vibrations. The Circuit Construction is quite simple. L1 is 3.25 turns in spiral form and is an integral part of the PCB foil pattern. The two BC547 transistors can be replaced with (almost) any smallsignal NPN transistor, such as the 2N2222. The final stage is a BC557 PNP general purpose device. If you use different devices then you should select the 1M0 resistor for 5volts DC at the collector of the the first transistor. Select the 47K resistor for 3 4 volts on the collector of the third transistor. Here is the V5 component overlay drawing. Note that there is a modification: ** 818 pf "Green" Trimmer capacitor Circuit diagram of FM Bug V5 Construction The PCB is 50mm x 25mm, but the Copper side layout is designed bigger for clarity.While printing , scale down the image to 34% from the Printer property / Page setup. This gives a better resolution a little "Patchy" image.NEVER reduce the size of the layout from any image editing application because it results in "Zaggy" image, making the print unusable for the PCB making process . Please If you know how to make PCB either by "Direct Photographic" method or "Silk Screen Stencil " method, it won't take more than half an hour to complete the project!! but if not, there is an opportunity to learn the art of In House PCB fabrication. The first prototype is shown above, beside the battery powering it. The output power is about +10dBm which would theoretically give it 3.12 times the range (1.6Km) but I have only tested it using a handheld receiver with the TX laying on the bench indoors. But I got a comfortable 700 meters (and a few funny looks from our neighbors). Beginners always deny the Antenna! Its very important for the full transmission energy dessipation. A 26 28 SWG enameled copper wire used in Motor winding of Fan etc will do.A piece of length 75 cm ( 1/4 of the wave length ) does well but a shorter 23cm also performs well. You should be care full that the Antenna wire should NOT LYING over the PCB.It generate stray inductor with the PCB and when the coil is itself etched on the PCB, problem increases. Keep the Antenna hanging vertically free.
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Transcript of FM Bug Transmitter V5
26/03/2015 FM Bug Transmitter V5
http://ujjwalj.tripod.com/hobbies/electronics/fm_bug_transmitter_v5.html 1/3
3 Transmitter FM Bug Transmitter The Best
FM Wireless Microphone has been a very popular project with beginners and experienced constructors alike. I do however, receivemany requests for a higher powered circuit and better microphone sensitivity. Now I can introduce the new FM Wireless Microphone (v5),which also has a better frequency stability, over 1Km range (under ideal conditions) and is good on microphone sensitivity and eliminates thenightmare of a beginner THERE IS NO WOUND COIL!! it is the part of the PCB itself. This has been achieved by adding an RF amplifierbuffer (with 10dB gain) and an AF preamplifier to boost the modulation a little. This power is enough to receive the signals through aregular Sony/Aiwa Walkman radio, which is the best recourse to pretend you are enjoying music!, when you are required to monitor from apublic place.
The most critical component , from sensitivity aspect is the Condenser Microphone. In the early stage of this project, I used the "normal"mic used in TapeRecorder, which costed me just Rs 5, leading me to a rather disappointing project.The response of the circuit to feeblesounds, which we are interested in , was terrible.I used to speak "IN TO" the mic as if addressing a meeting.
Then , I got the special High Sensitive Mic used in Cordless Phone's Base unit from a local electronic component store. This opened anew world and it can even transmits sounds which no one can even hear, at the eavesdropping site.
The Mic should be directly exposed to the surrounding , may be through a slit in the enclosure, exposing just the "Front face" of the micon the surface. The Mic dose not require to be directed to the source of the sound for it can receive the reflected waves from the wall, ifpresent. But there should be no obstacle in the line of the Mic, at least 2 feet away, so that it can receive vibrations.
The Circuit Construction is quite simple. L1 is 3.25 turns in spiral form and is an integral part of the PCB foil pattern. The two BC547 transistors canbe replaced with (almost) any smallsignal NPN transistor, such as the 2N2222. The final stage is a BC557 PNP general purpose device. Ifyou use different devices then you should select the 1M0 resistor for 5volts DC at the collector of the the first transistor. Select the 47Kresistor for 3 4 volts on the collector of the third transistor. Here is the V5 component overlay drawing. Note that there is a modification:
** 818 pf "Green" Trimmer capacitor
Circuit diagram of FM Bug V5
Construction
The PCB is 50mm x 25mm, but the Copper side layout is designed bigger for clarity.While printing , scale down the image to 34% fromthe Printer property / Page setup. This gives a better resolution a little "Patchy" image.NEVER reduce the size of the layout from any imageediting application because it results in "Zaggy" image, making the print unusable for the PCB making process . Please
If you know how to make PCB either by "Direct Photographic" method or "Silk Screen Stencil " method, it won't take more than half anhour to complete the project!! but if not, there is an opportunity to learn the art of In House PCB fabrication.
The first prototype is shown above, beside the battery powering it. The output power is about +10dBm which would theoretically give it3.12 times the range (1.6Km) but I have only tested it using a handheld receiver with the TX laying on the bench indoors. But I got acomfortable 700 meters (and a few funny looks from our neighbors).
Beginners always deny the Antenna! Its very important for the full transmission energy dessipation. A 26 28 SWG enameled copper wireused in Motor winding of Fan etc will do.A piece of length 75 cm ( 1/4 of the wave length ) does well but a shorter 23cm also performswell. You should be care full that the Antenna wire should NOT LYING over the PCB.It generate stray inductor with the PCB and when thecoil is itself etched on the PCB, problem increases. Keep the Antenna hanging vertically free.
26/03/2015 FM Bug Transmitter V5
http://ujjwalj.tripod.com/hobbies/electronics/fm_bug_transmitter_v5.html 2/3
The PCB layout of the Fm Bug V5. To be down scaled to 34%
Get Zipped BMP file of the PCB layout
Component side layout of the Fm Bug V5
Completed Prototype
Tuning The tuning is straight forward. The Trimmer can easily tune the oscillation in the 88 108 MHz (3 Meters) band. To tune the transmittingfrequency, bring a standard FM radio in front of the mic and tune your preferred frequency. Now tune the trimmer until a "Feed Back"sound from the radio's speaker occurs. Tune in the middle of Zone where the feed back occurs. With Walkman, I found a Nobel Idea! placeone of the ear piece of the walkman in your ear, other close to the MIC. Do the same as for the standard radio.
Legal Warning Have fun and please be aware that the higher power of this project may render it ILLEGAL in your own country, what else you canexpect from Indian Telegraph Act, 1885!!. I can accept no responsibility and it is up to you to check that you may legally use it. I will acceptNO complaints from any country/state correctional facility. But frankly speaking , people do cross these limits!
26/03/2015 FM Bug Transmitter V5
http://ujjwalj.tripod.com/hobbies/electronics/fm_bug_transmitter_v5.html 3/3
