Showing posts with label fm. Show all posts
Showing posts with label fm. Show all posts
Sunday, November 10, 2013
FM Receiver MPF102
An FM regenereative receiver using a single FET and one audio amplifier IC.
FM Receiver MPF102 Circuit Diagram
FM Receiver MPF102 Circuit Diagram
Saturday, November 9, 2013
AN7415 FM Stereo Demodulator
The circuit shown is a stereo FM PLL demodulator designed based on the AN7415. C1 is the input coupling capacitor to block any DC voltage present on the multiplexed input signal. LED D1 is an LED and R1 is the current limiting resistor. C4 and C5 are DC decoupling capacitors to the output channels left and right. C2 and C3 are bypass capacitors for noise output channels left and right. POT R2 can be used to adjust the separation between channels.
The resistor R5 and capacitors C7 and C8 form a network of low-pass filter for the internal DC amplifier circuit (see block diagram AN7415). C10 is a filter capacitor for the internal amplifier circuit Schmitt trigger IC. C9 is a filter capacitor for the circuit wave surge inside the AN7415. Resistor R3, R4 and capacitor C6 POT set the time constant of internal VCO circuit. Therefore POT R4 can be used to adjust the frequency of the VCO. A control signal 19KHz frequency is available in 12 pin IC. The switch S1 can be used to activate and deactivate the forced mono.
The resistor R5 and capacitors C7 and C8 form a network of low-pass filter for the internal DC amplifier circuit (see block diagram AN7415). C10 is a filter capacitor for the internal amplifier circuit Schmitt trigger IC. C9 is a filter capacitor for the circuit wave surge inside the AN7415. Resistor R3, R4 and capacitor C6 POT set the time constant of internal VCO circuit. Therefore POT R4 can be used to adjust the frequency of the VCO. A control signal 19KHz frequency is available in 12 pin IC. The switch S1 can be used to activate and deactivate the forced mono.
Saturday, October 12, 2013
USB FM transmitter circuit
Heres a simple VHF FM transmitter that could be used to play audio files from an MP3 player or computer on a standard VHF FM radio. The circuit use no coils that have to be wound. This FM transmitter can be used to listen to your own music throughout your home. When this FM transmitter used in the car, there is no need for a separate input to the car stereo to play back the music files from your MP3 player.
To keep the circuit simple as well as compact, it was decided to use a chip made by Maxim Integrated Products, the MAX2606 [1]. This IC from the MAX2605-MAX2609 series has been specifically designed for low-noise RF applications with a fixed frequency. The VCO (Voltage Controlled Oscillator) in this IC uses a Colpitts oscillator circuit. The variable-capacitance (varicap) diode and feedback capacitors for the tuning have also been integrated on this chip, so that you only need an external inductor to fix the central oscillator frequency.
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| USB FM transmitter schematics |
It is possible to fine-tune the frequency by varying the voltage to the varicap. Not much is demanded of the inductor, a type with a relatively low Q factor (35 to 40) is sufficient according to Maxim. The supply voltage to the IC should be between 2.7 and 5.5 V, the current consumption is between 2 and 4 mA. With values like these it seemed a good idea to supply the circuit with power from a USB port.
A common-mode choke is connected in series with the USB connections in order to avoid interference between the circuit and the PC supply. There is not much else to the circuit. The stereo signal connected to K1 is combined via R1 and R2 and is then passed via volume control P1 to the Tune input of IC1, where it causes the carrier wave to be frequency modulated. Filter R6/C7 is used to restrict the bandwidth of the audio signal. The setting of the frequency (across the whole VHF FM broadcast band) is done with P2, which is connected to the 5 V supply voltage.
The PCB designed uses resistors and capacitors with 0805 SMD packaging. The size of the board is only 41.2 x 17.9 mm, which is practically dongle-sized. For the aerial an almost straight copper track has been placed at the edge of the board. In practice we achieved a range of about 6 metres (18 feet) with this. There is also room for a 5-way SIL header on the board. Here we find the inputs to the 3.5 mm jack plug, the input to P1 and the supply voltage. The latter permits the circuit to be powered independently from the mains supply, via for example three AA batteries or a Lithium button cell. Inductor L1 in the prototype is a type made by Murata that has a fairly high Q factor: minimum 60 at 100 MHz.
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| Layout PCB USB FM transmitter |
Take care when you solder filter choke L2, since the connections on both sides are very close together. The supply voltage is connected to this, so make sure that you don’t short out the USB supply! Use a resistance meter to check that there is no short between the two supply connectors before connecting the circuit to a USB port on a computer or to the batteries.
P1 has the opposite effect to what you would expect (clockwise reduces the volume), because this made the board layout much easier. The deviation and audio bandwidth varies with the setting of P1. The maximum sensitivity of the audio input is fairly large. With P1 set to its maximum level, a stereo input of 10 mVrms is sufficient for the sound on the radio to remain clear. This also depends on the setting of the VCO. With a higher tuning voltage the input signal may be almost twice as large (see VCO tuning curve in the data sheet). Above that level some audible distortion becomes apparent. If the attenuation can’t be easily set by P1, you can increase the values of R1 and R2 without any problems.
Measurements with an RF analyzer showed that the third harmonic had a strong presence in the transmitted spectrum (about 10 dB below the fundamental frequency). This should really have been much lower. With a low-impedance source connected to both inputs the bandwidth varies from 13.1 kHz (P1 at maximum) to 57 kHz (with the wiper of P1 set to 1/10).
In this circuit the pre-emphasis of the input is missing. Radios in Europe have a built-in de-emphasis network of 50 μs (75 μs in the US). The sound from the radio will therefore sound noticeably muffled. To correct this, and also to stop a stereo receiver from mistakenly reacting to a 19 kHz component in the audio signal, an enhancement circuit Is published elsewhere in this issue (Pre-emphasis for FM Transmitter, also with a PCB). Author: Mathieu Coustans, Elektor Magazine, 2009
MP3 FM Transmitter Parts List
Resistors (all SMD 0805)
R1,R2 = 22kΩ
R3 = 4kΩ7
R4,R5 = 1kΩ
R6 = 270Ω
P1 = 10kΩ preset, SMD (TS53YJ103MR10 Vishay Sfernice, Farnell # 1557933)
P2 = 100kΩ preset, SMD(TS53YJ104MR10 Vishay Sfernice, Farnell # 1557934)
Capacitors (all SMD 0805)
C1,C2,C5 = 4μF7 10V
C3,C8 = 100nF
C4,C7 = 2nF2
C6 = 470nF
Inductors
L1 = 390nF, SMD 1206 (LQH31HNR39K03L Murata, Farnell # 1515418)
L2 = 2200Ω @ 100MHz, SMD, common-mode choke, 1206 type(DLW31SN222SQ2L Murata, Farnell #1515599)
Semiconductors
IC1 = MAX2606EUT+, SMD SOT23-6 (Maxim Integrated Products)
Miscellaneous
K1 = 3.5mm stereo audio jack SMD (SJ1-3513-SMT
CUI Inc, DIGI-Key # CP1-3513SJCT-ND)
K2 = 5-pin header (only required in combination with 090305-I pre-emphasis circuit)
K3 = USB connector type A, SMD (2410 07 Lumberg, Farnell # 1308875)
Notice. The use of a VHF FM transmitter, even a low power device like the one described here, is subject to radio regulations and may not be legal in all countries.
source [ Link ]
source [ Link ]
Friday, October 11, 2013
Long range FM voice Transmitter circuit
This circuit shows how to build a super-sensitive, mini-powered FM transmitter consisting of a RF (radio Frequency) oscillator section interfaced with a high sensitivity, wide pass-band audio amplifier and capacitance mike with a built-in FET (Field Effect Transistor) that modulates the base of the RF oscillator transistor. Transistor Q1 forms a relatively stable RF oscillator whose frequency and is determined by the value of coil L1 and turning capacitor C4.
Part List :
R1_______15K
R2_______3K9
R3_______220R
R4,R5____1K
R6,R9____10K
R7_______390K
C1,C6____0.01uF
C2_______4.7pF
C3_______0.1uF
C4_______6-35pf trimmer cap
C5_______2.2uF
B1_______3V
L1_______Coil winding (see below)
Q1,Q2____PN2222
M1_______Special FET bypassed microphone
Assemble L1 :Form L1 by tightly wrapping eight turns of #16 bus wire on a #8 wood screw. Produces an eight-turn coil with an inner diameter of approximately 0.135 inches and lenght of about 0.625 inches. Insert in the proper hole and solder as shown.
Saturday, October 5, 2013
FM Receiver TV Tuner TDA7000
FM Receiver / TV Tuner TDA7000This simple one chip FM receiver / TV tuner will acquiesce you to accept frequencies from 70 up to 120MHz. With this baby receiver it is accessible to auto TV stations, absolute 88 - 108MHz FM band, aircraft chat and abounding added clandestine transmissions. It is a absolute accompaniment to any FM Transmitter abnormally if FM bandage in your breadth is actual crowded. TDA7000 receiver offers actual acceptable acuteness accordingly it will alike acquiesce you to auto weaker signals that cannot be heard on accepted FM receivers.
A accurate affection of presented TDA7000 FM receiver is a voltage controlled oscillator agnate to TV tuners that are acclimated in television sets. Abundance is acquainted by capricious the ascribe voltage to the oscillator. The advantage of this blazon of oscillator is that you can use approved 100K potentiometer to absolutely tune to a accustomed broadcast. Tuning can be performed abundant quicker and absolutely than by application a trimmer (variable capacitor). Trimmers will additionally about-face the abundance as you blow them area potentiometer will not. Trimmer additionally needs to be placed on receivers PCB to abbreviate the devious capacitance area potentiometer can be calmly placed anywhere you appetite because it will not be afflicted by any alien capacitance.
Wednesday, October 2, 2013
RF Fm 88 108 MHz 20W amplifier
This Fm rf power amplifier has 2 transistors from Philips : BLV 10 and BLW 87. The 2 rf transistors work in class C and this fm amplifier has a total gain of 21dB ( 100 X ) and efficiency 55 – 65%.
One low pass filter with 9 components ensures 60dB rejection on the second harmonic. There is no need for tune-up to cover the whole 88 – 108 MHz FM frequencies.
source [link]
One low pass filter with 9 components ensures 60dB rejection on the second harmonic. There is no need for tune-up to cover the whole 88 – 108 MHz FM frequencies.
source [link]
Tuesday, September 17, 2013
80 MHz 108 MHz FM transmitter circuit
Signals from the microphone in the fm transmitter is reinforced by Q1, Q2 with carrier frequency generator is determined by the C5 and L1. The frequency of the FM transmitter is in the range 80 MHz - 108 MHz. L1 can be made with as many as 24 e-mail wire wrap and 6 wrap. The following is a picture series for the fm transmitter fm transmitter referred to in article 2 of this transistor.
This fm transmitter antenna is connected to the mid point of the antenna length L1 and preferably between 8-12 inches. FM Transmitter is only used for experiment and learning materials are not to be used for day-to-day, because the use of FM transmitter frequency regulated and protected by law may be understandable.
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