Sunday, June 26, 2011

Build very low cost FM transmitter, use your TV antenna and transmit upto 4km range!!

 Here is the specification of the transmitter


1. No. of stage: 4
2. Frequency of operation: About 100MHz
3. Antenna type: Folded 300 ohms dipole.
4. Range obtained in free space: Up to 4km with dipole antenna 30 feet above ground level. More   range with yagi antenna.

Fig: Circuit diagram of the Transmitter


Brief Description:
The transmitter is built on a Printed Circuit Board. This board uses track inductor for L1, L2 and part of L3. The section built around Q1 is the oscillator section. Oscillation frequency is determined by L1, C4 & C5 which forms the tank. Actually C5 is the feedback capacitor. This is required to sustain oscillation. This also influence the operation of tank formed by L1 & C4. Modulation is directly applied to the base of Q1 via C2. A microphone is connected here to serve this purpose. You can alternately feed direct audio here after disconnecting the microphone biasing resistor R1. Q2, Q3 & Q4 gradually raises the output power up to the desired level.
As most of the inductors are PCB etched, there is practically very little frequency drift provided you use a highly regulated and ripple free power supply.
RF output from the transmitter is taken from the junction of C11 & C12. This is unbalanced output of around 75 ohms impedance. But a folded dipole is a balanced type antenna of around 300 ohms impedance. So we need to use a 'BALanced to UNbalanced transformer' or 'BALUN'. A 1:4 type BALUN is employed here for this purpose. Antenna connection is taken from this BALUN via a 300 ohms flat parallel feeder cable commonly used in television to receive terrestrial broadcast. No coaxia is used to feed antenna. This saves cost. Also a parallel feeder cable provides much less signal loss compared to a coaxial.

 Click 'Read More" to see details with pictures

Design of BALUN
The BALUN is made using a two-hole binocular ferrite bead as shown above. You need to use parallel insulated twin wire to construct this. This wire is commonly used to wind TV BALUN transformer. If you want to get rid of this, then buy a ready-made TV BALUN that is generally used at the back of your television set for interfacing with feeder wire.
If you prefer to build this yourself, the circuit diagram is given above. You need to carefully construct it keeping in mind about the 'sense' & 'direction' of turns. See there are four coils. Two coils in the upper section, which are red and blue, required to be wound on left side of the BALUN and the remaining two (blue & red) in the lower half to be wound on right side. Connection marked 'A' and 'B' at the left side of the circuit is reqired to be connected to the PCB at the shown point. As dipole antenna is balanced type, so you need not to worry about its connection.





 PCB design details
The transmitter is built on a single sided PCB. As mentioned earlier, this PCB has a number of etched inductors. For this reason, you need to very carefully construct the PCB as mentioned below.


The above drawing is the copper side and below shown is the component mounting plan.


In the copper side view, you can see that there are three track etched inductors that resembles 'RCL' Every corner and track width/length are calculated and then they are drawn so that each 'RCL' section becomes an inductor of required value. Never play with this; otherwise, optimum result could not be achieved.
You need to use a laser printer or a high quality printer to get a printout of the drawings. First, save the picture to disk. Now try to print it from such a software which permits you to control print size. 'Paint Shop Pro' is such a software. Of course you can use any other software. Print the drawing so that copper side drawing is exactly 59mm X 59mm. Few trial will give you the perfect print. Now construct the PCB using 'Photo-etching' method so that all the tracks becomes exactly same as you are now seeing. Now drill the PCB carefully. The PCB is now ready to populate.
Start population according to the component mounting plan. You can also get a true size copy of this plan printed and glued to the PCB. This will help you work fast.Part of L3 is required to be constructed. This is described in parts list.
Please note that in the picture of the transmitter kit, capacitor C1 & C10 are not mounted by mistake and the kit is filmed. Please add these two capacitors. Try to keep all component leads as short as possible.
Now you need to design the dipole antenna to use with the kit.

N.B: Believe it or not, a 2N2369 from Philips, used in the final power amplifier section, can give this much of range. 


Detailed Parts List:

RESISTORS
R1 - 22K
R2 - 100K
R3, R7, R9 - 1K
R4, R8 - 100E
R5 - 390E
R6 - 330E
R10 - 15E
R11 - 10K
CAPACITORS
C1, C3, C10 - 1n
C2 - 100n
C4,C8,C9 - 47pF
C5, C11 - 10pF
C6 - 100uF/25V Electrolytic
C7 - 100pF
C12 - 3pF
TRANSISTORS
Q1, Q2, Q3 - BC548
Q4 - PN2369 (Plastic casing) or 2N2369 (Metal casing)
MISC.
L3 - 7 turns, 22SWG wire, 3mm ID, Close wound, Air core.
Two hole binocular BALUN core, BALUN wire, 300 ohms TV feeder wire,
JP1 to JP5 - All jumper wires.
This completes the Project. Please mail me with your feedback. It will really encourage me to give you more & more project like this.
 

Success story, making of my FM Transmitter.

I've tried to build (make) my own Fm transmitter from the very beginning of my boyhood but failed failed and failed. My first successful Fm transmitter was aired in 2001 when i was a student of class 12. After a long run of  4 years from class 9.

here i'll show you my recent 10 watt Fm transmitter testing circuit (battery powered exciter only due to security matter) and finally assembled cabinet (AC powered). 




 Transmitter after assambled

 Click "Read More" to see the other photos........



 close view


Heart of FM transmitter (the exciter)

Friday, June 17, 2011

ANTENNA DESIGN FOR FM TRANSMITTE

 ANTENNA DESIGN

There are two types of antenna for FM TRANSMITTE
1. Ground pole Antenna    
2. Half-Wave Dipole Antenna
A ready made GP Antenna. 


1. Ground pole Antenna(GP)

This Antenna is most widely used all over the world. For example, when you see a police car it has a transmitter with Ground Pole Antenna The body of car serves as ground). It accepts load from 50 ohm source and has larger power output than Half-Wave Dipole Antenna.


Frequency
Radiator - B
Radials - A
108MHZ
660
693
104MHz
684
720
100MHz
713
749
90MHz
792
819


 2. Half-Wave Dipole Antenna Or Open Dipole Antenna

It accepts load from 75 ohm source and has much smaller power output than Ground Pole Antenna. Use this antenna only when you don't have GP Antenna.
Construction: Two aluminum rods ,each of length "L" in meters are joined together through an insulator as shown in fig. From center, 75 ohm cable is feeded just like ordinary TV antenna.




I'll discuss the design, calculation of length, wire to be used and set-up details of FM TRANSMITTER Antenna very soon in this blog. so stay tuned.


Thursday, June 16, 2011

1 Watt simple FM Transmitter with 1-2 km range!

1 Watt FM Transmitter


This is simple 1 Watt FM Transmitter circuit. This circuit will be able to cover 1-2 KM range with a single pole antenna of 20 feet! 


Click on picture  to view the large size

Descriptions:
P1 act as condenser microphone volume level. For FM, coil will be small. Use thin gauge enamel magnet wire. the diameter of coil will be a couple mm: use ink tube from pen to form, and try 8-12 turns. Small inductance coils make for much guess work.

Components/parts  List:

R1=220K
R2=4.7K
R3,R4=10K          
R5=100ohm
C1,C2=4.7uF Electrolytic
C3,C4=1nF
C5=2-15pF
C6=3.3pF
Q1=BC547C
Q2=2N2219A
P1=25K MIC=Electret Condenser Type


Construction of Air Core Coil for FM transmitters

Just follow the steps as shown in the following pictures to make the air core coil for your Fm transmitter






                           Click  "Read More" to view details





 1. Select magnet wire of specific gauge as described in circuit (buy from motor/fan repairing shop).



 2. wound (round up) the wire on a pencil, pen or screw driver of correct diameter as stated in circuit diagram.


 3. don't make any half turn without any guide from your circuit text. Remove the pencil, pen or screw driver .


 4. Your Coil is almost ready, Cut the extra length of leg's and solder the both leg (pins) of your coil. try to keep the length of leg as minimum as possible. it'll give stability of your frequency.


 5. Shrink or expand the coil as the required length as stated in your desired circuit text.



 6. Here is your coil










Simpliest 2 watt FM transmitter with PCB and details


 USE DIPOLE ANTENNA FOR MAXIMUM RANGE (COULD BE UP TO 10 KM IN GOOD WEATHER). TUNE BETWEEN 88-108 MHz WITH C5. BB-204 COULD BE REPLACED WITH CONVENTIONAL LED (BIG) WITH REVERSE BIAS (NO LIGHT GIVEN IN CORRECT POLARITY). 9V POWER FOR 2KM WITH GOOD SOUND QUALITY AND GRADUALLY UP TO 18V FOR 10 KM RANGE WITH POOR QUALITY OF SOUND.  BEST OF LUCK. 








www.fmradio-transmitter.blogspot.com

USB 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)