BIG BRAIN TECHNOLOGIES: broadcast

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Monday, December 30, 2013

FM Radio Station Specs Part 23

FM RADIO STATION SPECS PART 23
FM Radio Station statement of operating specifications, characteristics and purpose

Specifications
Radio Type - Transmitter
Band - FM
Frequency Range - 88-108 MHz
Frequency Selection - tunable
Transmit power - under 100 mW
Range - desktop within room
Antenna - 1.75" diameter mini loop wire strand
Applications - hobby, school electronics, toy
Use - intermittent, testing, educational
Type - Personal Non-commercial
Power - 3 volts low power
Audio Source - voice electret microphone
Power source - battery
Typical Broadcast Duration- 30 seconds
Location - desktop
Size - pocket portable
Cost $4

Objectives
* to fulfill the requirements of electronics design lab
* testing fm transmitter characteristics
* learning principles of broadcast radio stations

Applications
* Transmit short range robot speech
* Classroom radio station project
* Electronics lab requirement
* Baby monitor
* Wireless pickup for guitar or ukelele
* Wireless microphone/KTV Singing
* Hobby or toy

Conclusion The micro FM radio station is a learning toy with short desktop range, a 1.75" antenna, and power under 100 milliwatts. No license is needed.

Sunday, December 29, 2013

FM Radio Station Housing Part 20

The idea is to put the radio station electronics into the smallest tiny enclosure possible and have remaining space for expansions. The yellow project box is perfect for this application, at 2 3/8" high x 1 1/8" deep x 4 1/8" long. One key feature, not shown here, is the front panel design label, that notates various controls and functions. Notations on the front will line up with actual controls at the top and the sides.

Cabinet, board, battery, antenna, controls

FM RADIO STATION TINY HOUSING PART 20
Perhaps the smallest radio station on the air today, tiny "Whisper Radio FM 102" is housed in a miniature cabinet with space for expansion.

Whisper Radio -
"To hear a whisper you need to shut out the noise of the world…"

The radio station housing is an insulated rectangular yellow polymer cabinet. Components on the inside include the main board on the left with protruding microphone at top and antenna on the left, plus a 9VDC battery over on the right side.

At the top left is the mic, and at the top right is the on/off toggle switch and a red LED power-on monitor light. The best feature of mounting the microphone this way is the shortness of the leads which are kept at only one fourth inch long, thus minimizing interference. The push through microphone, without extending the leads, creates the highest quality, best signal, and minimizes distortion.

The cabinet is "drilled" with a soldering iron that easily melts holes into the plastic. Keep the internal board to the left, close enough to the side wall but keeping clearance mounting space to include the antenna jack.

The cabinet is large enough for installing many added features described in previous posts, like the mute switch, on-the-air monitor, tone control, etc. Refer to the controls post and the index link for more details.

FM Radio Station Controls Part 9
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-controls.html

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

FM Radio Station Broadcast Part 19

SciFi broadcast on Whisper Radio FM 102

FM RADIO STATION BROADCAST PART 19
Whisper Radio FM 102 broadcast a science fiction program, The Experiment - the Adventures of Tom Volt, on Monday December 30th 2013 at 12:30 to 12:48 am. A transcript of the program's text is found at the link below. This is from the famous Tom Volt adventure series authored by science fiction and science fact writer Humanoido.

The story goes on about the opening up of a quantum door into an alternate reality by a small group of scientist and describes their ultimate experiences.

The Adventures of Tom Volt - the Experiment
http://humanoidolabs.blogspot.tw/2013/04/the-experiment.html

FM Radio Station Schematic V1.1 Part 18

FM RADIO STATION SCHEMATIC V1.1 PART 18

The new updated v1.1 schematic for the FM radio station adds polarity notation to the electret microphone, corrects the size of notation for C3, and cleans up the antenna A1 symbol. It corrects the notation for transistors as Q1 and Q2 instead of T1 and T2, and introduces scaling.

A larger percent size schematic is provided for better clarity.

For more details about the FM Radio Station, refer to the index link.

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

FM Radio Station Electronics Part 17

FM RADIO STATION ELECTRONICS PART 17

This page assembles four important comparison electronic element views showing the FM Radio Station. The purpose is to check the components and their placements from the board to the schematic to confirm complete accuracy so the project can be duplicated.

At top left is the top side of the printed circuit board showing all components and their values.

At top right, the photo shows a back lit view with circuit traces.

At bottom left is the schematic diagram.

At bottom right is a photo of the bottom side, with photo reversal to match the top right back lit photo.

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

Friday, December 27, 2013

FM Radio Station Microphone Part 15

FM RADIO STATION MICROPHONE PART 15

Electret Microphone
http://sound.westhost.com/project93.htm

A typical electret microphone preamp circuit uses an FET in a common source configuration. The two-terminal electret capsule contains a FET which must be externally powered by supply voltage V+. The resistor sets the gain and output impedance. The audio signal appears at the output, after a DC-blocking capacitor.

THE MICROPHONE is an important part of the radio station. In a simplified circuit, it must deliver reasonable sound quality and provide a usable frequency response and audio level.

An electret condenser microphone (ECM) consists of a very light diaphragm (moving plate) and back plate (stationary or static plate) and has a permanent charge implanted in an electret material to provide polarizing voltage.

The principle of operation is that sound waves impinging on the diaphragm cause the capacitance between it and the back plate to change synchronously, this in turn induces an AC voltage on the back plate.

1. Foil Electret Condenser Microphone (also called Middle or Classic) - Type of condenser microphone where the electret material is the diaphragm. (Sometimes referred to as "Front" type.)

2. Back Electret Condenser Microphone -Type of condenser microphone where the electret material is the back plate.

3. Front Electret Condenser Microphone -Type of condenser microphone where the electret material is the inside of the case of the microphone.

"It must be realized that all electret mics (indeed, all mics) have one limitation we cannot readily change, and that is maximum SPL (Sound Pressure Level). Because electret capsules have an integral amplifier, there will always be a level where they will distort.

A capsule having a 10k feed resistor and supplied from a 15V supply will output well over 1V RMS quite easily, simply by having it close enough to your mouth as you speak loudly.

Even professional microphones (including dynamic types) are quite capable of 0dBm in close proximity to a floor tom or a loud singer. As a result, close vocal work, drums and brass instruments (trumpet, sax, etc) are capable of extremely high SPL, and are not really suitable candidates for electret mics. It is possible to get good performance at up to 115dB SPL quite easily - possibly more.

Sensitivity
The sensitivity can be reduced, simply by reducing the value of the feed resistor. Again, there is a limit, as the internal FET amplifier can be driven into distortion regardless of what you do on the outside of the capsule. It is feasible to modify the capsule itself - but this is only possible with some models unless you are willing to make a few sacrifices (you can guarantee that you will ruin a couple in the process)."

Frequency response
http://www.digikey.tw/Web%20Export/Supplier%20Content/PUI_668/PDF/PUI_ElectretCondenserMicrophone%20Basics.pdf?redirected=1

"Frequency response is the microphone's sensitivity performance in the frequency range of 0 to 20 kHz. Compared with the dynamic types, ECMs tend to have an extended response both at low and high frequencies, which is also smoother.In the case of dynamic types, the response limits are defined where the sensitivity has fallen by 3 dB relative to its value at 1 kHz. It is not stated in such terms for ECMs since they have a much wider frequency response."

Usage

"To obtain the best results, avoid placing near reflective surfaces. If possible, mount in soft rubber to insulate from vibration. Treat ECMs as stat ic sensitive. Use specified heat sinking when soldering to ECMs. Use as little heat as possible for shortest time consistent with good joint. Avoid subjecting ECMs to high temperature and humidity that can degrade performance. The frequency response of ECMs may be too extended for communications application, in which case, it can be limited by suitable acoustic filtering in the intended housing or handset."

Microphone Setup
The legs on the electret microphone can extend through the cabinet. The mic is supported using a single strand color insulated copper wire. The mic electrical cable has a negative shield side to reduce interference. The microphone has a foam covering fabricated from a discarded headset. The wire support is bendable for best positioning.

Microphone Modifications
One improvement, since moving very close to the mic produces a much better signal and greater clarity, is a funnel that can direct the sound into the mic. This may be a great improvement and needs further testing. It may resemble a miniature old fashioned Thomas Edison "Gramophone." The cone can be fabricated from paper, cardboard or plastic from a bottle.

Microphone Measurement
The microphone resistance is measured at 1.37 ohms.

Microphone Impedance
http://www.edaboard.com/thread217554.html

http://www.gearslutz.com/board/geekslutz-forum/764918-what-should-follow-electret-mic-capsule.html

Definitions
SPL - Sound Pressure Level

Microphone - Receiver that converts sound energy to electrical energy. Also described as a sound sensor.

Condenser - Another term used for a capacitor: two plates separated by a fixed distance capable of storing an electric charge.

Electret - An electrical property which describes the capability to retain electrical charges.

Pascal (Pa); bar (1Pa = 10 u bars) - Unit of pressure. For microphone applications, this unit refers to
the pressure of sound on a microphone.

Links
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-controls.html

http://en.wikipedia.org/wiki/Electret_microphone

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

FM Radio Station Mute Function Part 14

Radio Station mute function schematic

FM RADIO STATION MUTE FUNCTION PART 14

This circuit shows details for adding a mute function to the FM radio station. A switch will mute the microphone. When muted, the LED will stay lit.

Microphone Mute Function with LED monitor
When the DPDT switch is in a normalized position, the electret microphone is active, the LED is not connected, and broadcast takes place. When switched, the microphone cuts out, resistor R2 is connected to replace the microphone, and the LED lights. A carrier signal continues to broadcast but there is no sound. The LED is on a separate circuit and does not interfere with the microphone. The microphone resistance is measured at 1.37 ohms (when not in the circuit).

Note: On the schematic, replace the text SPDT with DPDT.

http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-controls.html

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

Wednesday, December 25, 2013

FM Radio Station Controls Part 9

FM RADIO STATION CONTROLS PART 9
Over time, the simple FM Radio Station will have upgrades for more controls and more functionality. Below are numerous possible combinations.

Spartan "Basic Two" Radio Station
On/Off Switch
Power On Red LED
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-power-monitor-mod-part-13.html

A very spartan version with rudimentary controls is possible by using a rectangular project box with a hole for the mic protrusion and holes for the on/off battery switch and red LED.

Four Version Radio Station
On/Off Switch
Power On Red LED
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-power-monitor-mod-part-13.html

The on/off is a toggle switch wired to turn the 9 volt battery supply on or off. The LED wires in with the on/off switch and a dropping resistor to the LED to indicate when power is on.

Mute Switch
On the Air LED
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-mute-function-part-14.html

Another handy feature is an audible mute switch for the microphone. This cuts out the microphone and switches to a resistor with the same resistance as the microphone. The result is a transmitted broadcast carrier frequency without any sound from the microphone.

Deluxe Version Radio Station
This deluxe radio station version has many more advanced controls bringing it closer to a professional radio station.

Switch On/Off
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-power-monitor-mod-part-13.html

Switch External Antenna A or B
The external antenna switch requires two antenna banana jacks to plug in two antennas at the same time. The switch can enable antenna A or B.

Switch Power from 9V Battery to External Power Jack
A switch that powers off the 9 volt battery supply. Then, the banana power input jack can accept a lower voltage such 6 volts or 3 volts DC and/or simply run off an external power supply instead of internal batteries. This will affect the transmitters power and range. In some cases, it may be useful and necessary to reduce power and range to comply with local regulations.

Switch Mic Mute
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-mute-function-part-14.html

Audible mute switch for the microphone. This cuts out the microphone and switches to a resistor with the same resistance as the microphone. The result is a transmitted broadcast carrier frequency without any sound from the microphone.

LED Power On/Off Red LED
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-power-monitor-mod-part-13.html

LED On the Air White LED
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-mute-function-part-14.html

Tone Selector
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-tone-part-16.html
A tone selector switch is used as a high pass filter to provide some tone adjustment. The first setting at 47nF reduces the low frequency and puts more of the mid-range into useful talk power. For FM, the second setting uses a 1uF capacitor which provides more full range audio suited to FM voice.

Sensitivity Control
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-sensitivity-part-21.html
This modification replaces 1K resistor R1 with a 10K potentiometer to adjust the sensitivity of the microphone and the transmitter signal.

FM Radio Station Shielding
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-shielding-part-22.html
The install of aluminum conductive ground shielding, inside the radio station housing, will minimize frequency shift and interference from outside sources such as a human hand.

Banana Jack External Power Supply Black (- ground)
Banana Jack External Power Supply Red (+ 9 volts max)
These are two banana jacks to plug in an external power supply

Banana Jack Ground (plug in for antenna load)
Banana Jack Antenna
These are two banana jacks for two purposes. One, the plug in antenna and ground allows plugging in a light bulb load to determine power output and run tests. Two, an external antenna can plug in.

Banana Jack External Sound Input
This jack is for plugging in an audio source like an iPod, iPhone, or iPad. It can input a source of music or prerecorded programming for FM radio station broadcast.

Control Variable Volume
The variable volume control sets the volume of the input microphone.

Amplifier Monitor Headset
This is an amplified sound monitor that feeds the mono broadcast sound to a headset for monitoring purposes. The amplifier is an LM386 chip. The circuit requires audio conversion.

2 Sound Source Mixer
This is a basic two source sound mixer. It can mix one sound source with the microphone. It uses the External Sound Input and a control "mixing" knob.

Band - With different switchable or plug style "band" coils, it would be possible to make large changes to the transmitting frequency. It may be more feasible to interchange values of capacitors. With proper orientation, either the band coils or the capacitors could plug into the cabinet to enable particular transmit frequencies.

Trim - With a variable 0 to 20 pF capacitor connected in parallel with the coil, it would be possible to fine tune the transmitting frequency.

Clock - with added processor, a clock is an added feature useful for keeping programming on time

Compass - with added processor, a compass can verify the same equipment and antenna positioning, since position greatly effects transmission and signal characteristics

Program Timer - with added processor, a timer is useful for keeping programs on schedule

Program Timer Switch - with added processor, a timed switch can automate the start of radio programs

Signal Strength - the idea is to determine the strength of the signal being transmitted, using a common DVM and/or pickup coil to calibrate the transmitter to under 100 mW to comply with FCC Part 15 regulations in the USA. Also refer to the installment blog about determining power.
http://humanoidolabs.blogspot.tw/2013/12/radion.html

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

Tuesday, December 24, 2013

FM Radio Station Broadcast Script Part 8

For FM radio broadcast testing, the green solid strand wire loop antenna was formed into a 1.75-inch diameter circle and soldered to the printed circuit board. The close proximity of the radio is for illustration only. The antenna and the transmitter are directional.

FM RADIO STATION BROADCAST SCRIPT PART 8
This is a list of broadcast script from the FM radio station on day 1 through 3 of part time operations. The determined test frequency is currently 102 MHz on the FM band.

Monday December 23
Two days before Christmas, at 10:00 pm, the radio station was turned on for the first time. A nearby FM radio was scanned across several transmitter harmonics, then settled onto the strongest signal. It's a success! "Testing, testing, 1, 2, 3..." came in loud and clear on the small portable radio tuned to the FM band. This was repeated several times.

Tuesday December 24
On Christmas Eve around 11 pm, this special transmission went out for holiday wishes and additional tests were completed. "Have a happy holiday and Merry Christmas." The script was repeated prior to running tests.

Wednesday December 25th Christmas
At 1:00 am to 1:30 am, for tests, "Roger Rabbit" was repeated which verified the frequency orientation shift. For each Roger Rabbit, a new orientation and frequency shift was tested. Microphone positioning was established along with the notation of characteristics from human positioning. In particular, the coil is sensitive to human positioning and will need to be in a retracted position during future operations.

Signal Propagation
Again, with a 1.75-inch green loop antenna, which is very cute by the way, we're not exactly sure who heard the signal other than ourselves in the Lab due to the given "in house" range.

QSL Cards
If and when we are able to extend the range to another room, we'll think about making up a batch of QSL Reception Verification Cards for "send out" to our... er... colleagues.

Radio Station Name
Prior to the design of QSL cards, the radio station will need a name, something like Whisper 102 Radio...

Broadcast Schedule
Later we will present the Whisper Radio 102 broadcast schedule for the New Year!

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

FM Radio Station Testing Part 7

The 9-volt powered mini radio station is set to broadcast on the FM band near 102 MHz with more tests using a tiny 1.75-inch circular loop antenna. Today's tests include a harmonic and range study, along with orientation reviews. A very sensitive Chinese multi band radio is at the receiving end. The photo does not show the actual test range distance. In this second day "on the air" test, a small script will be sent out over the "air waves." Stay tuned to this project and the radio station just keeps growing and growing.

FM RADIO STATION TRANSMITTER TESTING PART 7
The next phase of the radio station is testing and calibration of the transmitter and equipment, and running more experiments to pace the radio station and see what works best.

* Range
* Transmitter Signature Footprint
* Detail & Extent of Harmonics
* Quality with Microphone
* Background Pickup Determination
* Orientation Positioning Effects
* Results of interchangeable Antenna
* Results with Different Antenna Designs
* Signature of Transmissions with Antenna Position
* Effects of Antenna Blockage
* Types of Material and the Effects on Wireless
* Results of Direct Audio Feed Bypassing Mic
* Results of Varied Lower Power Voltage
* Instrumentation Add On
* Mute Circuit Resistor Determination
* Power Determinations

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

Monday, December 23, 2013

FM Radio Station Programming Part 6

FM RADIO STATION PART 6 PROGRAMMING
This is a suggestion guide to potential upcoming broadcast programming for the Lab's FM radio station.

* Laboratory Testing

* Atmospheric/Weather Conditions
* Sky Pollution Rating and Forecast

* Scientific Lab News/Discoveries
* Extremely Powerful Telescopes

* Big Brain Machine Supercomputer
* Machine Brain Technology (i.e. Brain in a Jar Project)

* New Invention Zone
* Projects (Progress Reports, Updates)
* Vintage Music

* Mysterious Spell-Bound Science Fiction
* Strange Science Fact

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

FM Radio Station Part 5 Index

FM Radio Station Part 4 Broadcasting

THE VOICE OF SCIENCE NOW BROADCASTING... Connected to a 9-volt battery, this is the first power on of the radio station. We're on the air, with an antenna so tiny, it's merely broadcasting to the other side of the table. This is the first successful test of the FM radio station with "across room range." There's always excitement when a "just built" project is switched on for the first time. It's always hoped that it works perfect the first time. Building projects is like a crap shoot - there's any number of things that can go wrong as Murphy's law dictates. In the case of projects, components often have a 10% failure rate and can cause some frustration in troubleshooting newly assembled projects. One can take a gamble and assemble the parts untested, or test each part for greater workability insurance. With this project, the radio station worked perfect the first time!

FM RADIO STATION transmitter broadcasting part 4
We're broadcasting into space! Who is listening?

This is the fourth installment about building your own radio station. On Monday December 23, two days before Christmas, at 10:00 pm, the radio station was turned on for the first time. A nearby FM radio was scanned across several transmitter harmonics, then settled onto the strongest signal. It's a success! "Testing, testing, 1, 2, 3..." came in loud and clear on the small portable radio tuned to the FM band.

The transmitter's coil was slightly adjusted to push the signal farther up the FM band to avoid several very strong radio stations around 98 to 100 MHz. The perfect test place was quiet at 101 and 102 MHz.

For initial testing, a tiny loop antenna is used which extends only about 3-inches high in the long direction when elliptical and is about 1.5-inches diameter when circular, perfect for across-room broadcasting.

The sensitivity is capable of overloading acoustical feedback and distance of the audible source to the mic is also sensitive. The orientation of the transmitter greatly effects reception and keeping it in one place is required. Hands near certain areas of the transmitter effect frequency and harmonics, although the portable FM receiver is ultra sensitive - a 10 band FM/MW/SW World Receiver model 6110 by Panda made in China. Its FM band ranges from 76 to 108 MHz with manual tuning and running from 3-volts. This radio was used for reception of objects in space such as the planet Jupiter and the Earth's Sun during the Lab's SETI program searching for extraterrestrial intelligence.

Radio Telescope Receiver
http://humanoidolabs.blogspot.tw/2013/07/radio-telescope-receiver.html

Don't Eat Us Safety Program Radio Telescope
http://humanoidolabs.blogspot.tw/2013/07/dont-eat-us-safety-program-radio.html

Radio Telescope Adds Spaceweather Radio
http://humanoidolabs.blogspot.tw/2013/07/radio-telescope-adds-spaceweather-radio.html

Radio Telescope Observatory Lab 58
http://humanoidolabs.blogspot.tw/2013/07/radio-telescope-observatory-lab-57.html

The FM band in this region of the country, serving up to 24 million people, contains strong stations in almost every position on the band from 76 to 108 MHz. Smaller stations serve a six million locality. Therefore the density of stations is unprecedented. Many of these stations may be underground as the government is working to license and annex these broadcast stations.

A weak station, or even one that has associated harmonics, will be lost in the signal hash, thus limiting the range.

The unexpected high quality of the FM transmitter is very good when trimmed and tuned. Voice is very audible close to the microphone. Backgrounds sound muted as desired although this requires more sensitive testing.

The high quality of such a simple circuit is attributed to the high quality of the parts used, i.e. the special am/fm, rf, amp, mix, conv, osc and IF ability of the 2SC1675 transistor, and the 1-watt output amplifier of radios in class B push-pull operations ability of the 2SC9013 transistor.

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

FM Radio Station Part 3 Assembly & Tips

Fully assembled and ready for testing, the FM transmitter radio station is shown with a potential cabinet housing. Note how the microphone is repositioned top side for ease of positioning inside and through the yellow cabinet.

assembly and tips
HOW TO BUILD YOUR OWN FM RADIO STATION TRANSMITTER PART 3

PARTY TIME!!! Today is a solder party. Get out your guns (soldering guns) and prepare to melt some metal, putting metal (tin) on metal (copper).

Tuning the frequency
By a bit of trial and error plus observation with a nearby FM radio receiver, it is possible to tune the FM transmitter. Using the coil, either expand or compress the wire coils to change the frequency. A closer wire gap give a lower frequency and a loose wider spacing gap gives a higher frequency.

The completed solder side of the printed circuit board with a green loop antenna about 2.75-inches high and a microphone set outwards on one side to facilitate a good fit through the cabinet top. Prime use of this project is to fulfill the authors objective to own and operate a tiny radio station (at the toy level) - in this case, a tiny exampling FM band transmitter that can send broadcasting from one side of the table to the other side.

Apps won't end there as the transmitter can have audio signal input into its stage, such as a Parallax Propeller chip's voice speech synthesizer signal inside the electric brain in a jar, and then transmit a speech signal through the jar, speaking wireless into a nearby radio. Building one transmitter is very cost effective at US$4.

When soldering the electrolytic capacitors and the transistors, use a heat sink on each of the wire leads to prevent component damage from heat.

It is also possible to change the value of the ceramic capacitor which is in parallel with the coil. Some designs use a tunable variable capacitor to do the tuning. In this case, the variable capacitor would have a tunable range from 0 to 10 pF. Since this transmitter has no requirements for specific FM frequencies, the variable capacitor is not needed.

Experiment with the coil spacing first to determine the range. Keep the receiver at distance from the transmitter to minimize the reception of spurious radio signals. Make sure you've found the primary signal which will have the greatest signal strength.

Reference this image showing a different orientation for clarity, to the photo in post part number 2 for circuit path positions. Note the coil spacing to change the frequency to a "quiet spot" on the upper FM dial.

The 10 pF capacitor is set to match the number of turns on the coil. With a greater capacitor value such as 20 or 50, the number of coil turns would be too much.

Antenna Length
First, here are some "getting started" approximate values already calculated for some frequencies. A full wave antenna for 98 Mhz, the center of the FM band, would be 119 inches. A half wave would be 59 inches. A quarter wave antenna for 98 Mhz would be 29 inches long. Try an eighth wave antenna at 14 inches long or a sixteenth wave antenna at 7 inches.

Online Whip Antenna Calculator
http://www.csgnetwork.com/antennagenericfreqlencalc.html
For more precise values, enter the frequency and the online program will calculate half and quarter wavelength whip antenna size. Requires browsers with enabled Javascript. "This calculator is designed to give the vertical length (height) of a particular whip type antenna, or the frequency of it. Enter one (only one) value, the desired frequency or the antenna length in any length field. Click on Calculate and the opposite value will be displayed in feet and inches or frequency in megahertz (Mhz). These are considered as generic calculations and you may wish to use them to learn general information about the antenna structure you are contemplating. Click on Clear Values to prepare for new calculations. Any antenna created with this calculator MUST be fine tuned for VSWR. None of the calculations are rounded or massaged and all calculated results are raw data."

Frequency Stability
The frequency may drift as the battery voltage becomes less. This is expected with this simple design. To offer more regulation, one could use a regulated power supply instead of the battery. The simple design presented here for exampling will use fresh batteries and some frequency drift will be expected. Do not use an AC adapter as these are generally not regulated and introduce interference.

Use with iPod, iPhone, iPad
"The earlier model of iPod has an automatic shut-down system in it. When you pull out the plug of your headphone, it automatically stops working. When the left and right channels are short-circuited, the same thing happens. Presumably, you can use a stereo cable and solder the left (white) and right (red) lead together. Please use the left channel lead (white) only. Usually the left output is compatible with mono audio. If you, however, insist to mix the left and right output of your audio source into the transmitter, make a simple "interface" like this." Source: http://www.translocal.jp/radio/micro/howtosimplestTX.html

Radio Station Parts List
1 Resistor 820 Ohm
1 Resistor 4.7 K
1 Resistor 3.3K
1 Resistor 10K
1 Resistor 220K
1 Resistor 1K
1 Capacitor Ceramic Disc 10 pF
1 Capacitor Ceramic Disc .001 uF (102)
1 Capacitor Ceramic Disc .01 uF (103)
2 Capacitor Electrolytic 4.7 uF
1 Transistor 2SC1675 (or 2SC829) Q1
1 Transistor CS9013 Q2
1 Antenna Wire 16"
1 Coil (see text)
1 Electret Microphone
1 Printed Circuit Board
1 Enclosure
1 Printed Panel

Although controls are not necessary, adding a power switch and other capabilities may be desirable.

Spartan Version
On/Off Switch
A very spartan version with rudimentary controls is possible by using a rectangular project box with a hole for the mic protrusion and a hole for the on/off battery switch.

Basic Three Version
On/Off Switch
On the Air LED
Mute Switch
The on/off is a toggle switch wired to turn the 9 volt battery supply on or off.

The next upgrade can include a red LED for "on the air" monitor. This would wire in with the on/off switch and a dropping resistor to the LED.

Another handy feature is an audible mute switch. This would cut out the microphone and switch to a resistor with the same resistance as the microphone.

Deluxe Version
On/Off Switch
On the Air Red LED
Mic Mute
Variable Volume Control
External Sound Input
Signal Strength
Amplifier Monitor
Headset for Amp Monitor
External Power Supply
Switch from 3V, 6V, 9V (regulates output power)
2 Sound Source Mixer
External Antenna 1 or 2

Band - With different switchable "band" coils, it would be possible to change the transmitting frequency.

Trim - With a variable 0 to 20 pF capacitor, it would be possible to tune the transmitting frequency.

Clock - with added processor
Compass - with added processor

SOURCES
http://www.translocal.jp/radio/micro/howtosimplestTX.html

FM Radio Station Part 5 Index
http://humanoidolabs.blogspot.tw/2013/12/fm-radio-station-part-5-index.html

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