Thursday, December 23, 2010

Citrus Fruit Bad Liver

863-865 MHz

With two modules UHF 863-865 MHz, a transmitter and receiver are moving the signal from a microphone to an amplifier or mixer remote (up to 40 m). This two units TX and RX is ideal for someone who wants to move in a studio, a gym or on a stage, a stage, etc.., Talking or singing into the microphone. In short, this is a wireless microphone of high quality.





Specifications:
- Working frequency: 863 to 865 MHz.
- Max Range: 40 m - Frequency Response: 50 to 15,000 Hz
- Harmonic Distortion: 2%.
- Dynamic range: 50 dB. - Expander on TX and RX. The association between the entertainment and wireless devices (not to say "wireless", which means exactly the same thing) is now well established and for a decade. One can not deny that the availability of such RF microphones and other signal transmitters for musical instruments, like guitars or bass, or portable keyboards-has changed the lives of musicians, especially in concert, as well as presenters of artistic or television studios. With traditional microphones (strings attached), it was necessary to always be attentive to the movements that we would do, which excluded fantasy and spontaneity, yet so popular with the public! We could at any time in the heat of the speech or gambling scene, to carry the mixer or at least pull the wire, unless spread of self- full length! The wireless microphone gave the artist or entertainer all his freedom. And not only to professional: the market availability of consumer electronics products at low prices, has in a decade an unprecedented development of such equipment.
Recently we had the opportunity to try the modules RF Circuit Design (distributed by Sylcom Service www.sylcom.it) with which we achieved the professional radiomicrophone that this article describes and proposes to construct two units, issuing and receiver. The majority of radiomicrophones works with a carrier located in the frequency standard, free use, one that extends around 434 MHz. Other qualified products emit in the band of 40 MHz or between 174 and 854 MHz (see table in Figure 9). Ours emits between 863 and 865 MHz frequency used freely, provided they remain within the limits of power law (and the modules comply Circuit Design).
The transmitter unit

unit designed to send in ether audio is so simple and compact (see Figures 1-3) it can be easily installed (9V battery included) in " handle " a cardioid or other magnetic micro-called "scene" or it can be mounted in a tiny box to hide in a pocket (an electret alligator clip pinned to the collar of the jacket then routes the call to entry jack box). The wiring diagram of Figure 1 will appear "Spartan" because almost all functions are assigned to module U1 WA-TX-01 Circuit Design (a Japanese). Therefore analyze this circuit, we can see, consists of two functional blocks: a preamplifier transistor and the RF module.
The input stage is used to raise the level low BM taken at the output of the microphone, especially if one uses a capsule electret non-fading or a magnetic microphone, which normally provide RMS voltages of a few millivolts.
The preamp consists of a transistor connected in common emitter configuration: the NPN, polarized by the base through R3, return on its collector the amplified signal. The microphone is connected to the IN, to adapt the sending unit to a microphone "electretcondenser (electret condenser) or magnetic, we have provided the opportunity to provide the driver with" hot "a modest polarization taking on the bridge R1/R2 voltage we need. When using an electret microphone (one capsule "naked and raw" or a microphone clip alligator clip to the lapel or shirt collar), we must close J1 for the desired polarization ( C3 decouples the electrolyte continuously biasing network and the trimmer TR1), the rider must however remain open when the microphone attached to the jack IN is magnetic.
The electrolytic capacitor C4 is used to filter the polarization component in order to clean it of any parasites on line 9 V, which parasites, if not mitigated, would be amplified with the useful signal from the microphone, which would degrade the signal to noise ratio. C4 filter as potential positive returns by feeding the audio signal amplified by T1. Before being amplified by the transistor, the signal coming from the microphone can be adjusted in amplitude to the trimmer TR1 in order to avoid introducing into the transmitter module of BF levels may represent a significant distortion. Capacitor C5 decouples
continuous network bias base by trimmer T1, C6, while the audio signal to U1, while by decoupling pin 1 of the latter's collector of the transistor.
And we have come to the issuer itself: WA-TX-01, it is a component comprising a SAW oscillator internal modulator frequency variable capacitive reactance (varactor diode ...) and an antenna filter lowpass. The modulator stage is controlled by the audio signal, but not by those applied between point I and the ground (G), at least not always, indeed, the LF component introduced in the module goes through a compressor dynamics - a special electronic circuit designed to limit the dynamic range, the excursion between the minimum level of signal and its maximum level.
compression is used primarily for two things: increase the SNR and to avoid over-modulation, the modulation to understand, remember that FM transmitters in the carrier oscillates around the center frequency and deviation on either side of it (the tour or modulation depth) is directly proportional to the amplitude of the modulating signal. As each band defines a radio channel spacing, it is essential that during the excursion produced by the modulation, the transmission frequency does not encroach on one of two adjacent channels For example, if one transmits on 500 MHz and if the channels are separated from each other than 200 kHz, the tour due to the modulation must be less than ± 100 kHz (100 kHz on both of Another of the center frequency). Say that the frequency deviation of FM broadcast must always be less than half the distance between the channels; lower selectivity because of the oscillators and the issue of unwanted frequencies may not modulate down to half the distance , since the emission curve can not have edges perpendicular (infinite attenuation outside the scope of frequencies).
About this compressor, adding that it limits the voltage responsible for modulating the frequency deviation of the oscillator to allow the deviation values to remain within the limits allowed. Strictly speaking, we could obtain this limit by capping the modulating voltage, except that this method would cause a significant distortion of the demodulated signal at the receiver, while with the compressor is a variable gain amplifier circuit, which amplification is gradually reduced when a sensor detects that the level of amplitude of the audio input becomes excessive, however, increased when the signal level is too low.
The compressor compresses dynamics therefore the signal (yes) and does not significantly decapitated, to allow (provided that receipt is implement a balanced circuit) compensation from the flattening of the dynamic and obtain again the original signal. The compression is between -60 and -10 dB, which allows a range of 50 dB and therefore the signals below -60 dB are amplified up to this level and those greater than -10 dB are attenuated in return the magnitude at this level.
In terms of SNR, the compressor amplifies weak signals that the background noise of the FM (typically -60 dB) to put them above this level, therefore when, in the receiver, the Expander decompresses the signal modulating the same audio the lowest level can be used, since its amplitude is at least equal to the noise superimposed on the demodulated component. Module WA-TX-01 is supplied with the crystal oscillator set to one of three proposed frequencies: 863,125, 863,625, 864,500 and 864,875 kHz, and works basically in the range from 863 to 865 MHz, reserved, Europe , audio applications. Just choose the frequency you want and specify when ordering the unit to the dealer.
In the range 863 ÷ 865 MHz emission must be reduced in power: wherefore the transmitter emits only 2 mW, which is quite sufficient to provide a wireless microphone, provided that you also use the receiver module highly sensitive proposed by Circuit Design: we can then rely on a range of about 40 m in open space (without obstacles and using antennas as receiving and sending a piece of copper wire of 8.5 cm or 17 cm long). The transmitter (TX module and the input transistor) is fed with DC 9 V battery removed from a rectangular 6F22; the supply line is protected against accidental reversal of polarity by diode D1 and filtered by C1 and C2. A switch allows us to switch on and off the transmitter radiomicrophone without disconnecting the battery.





Figure 1: Diagram of the issuer.






Figure 2: Schematic implementation of the components of the transmitter.

Figure 2b: Drawing, to scale 1, the PCB of the transmitter.

Figure 3: Photograph of a prototype of the plate of the issuer.

Iist R1 ...... R2 1 k ...... 4.7 k R3
...... 1.5 M
R4 ...... 4.7 k TR1 ..... 10K trimmer C1 MO ...... 100 nF multilayer C2 ...... 220 uF 16 V electrolytic C3 ...... 4.7 uF 100 V electrolytic C4 ...... 47 uF 35 V electrolytic C5
...... 1 uF 100 V electrolytic
...... C6 10 uF 100 V electrolytic D1 ...... 1N4007 T1 ...... BC547
U1 ...... WATX01
SW1 ..... slide switch 90 °

Miscellaneous:
a stereo jack socket for an antenna tuned it
863-865 MHz

a rider taking a 9 V battery
a plastic housing potential

Remember to solder all pins and tabs on the transmitter module.



The receiving unit

See Figures 4-6. The signal from the WA-TX-01 is sensed by the receiver antenna and reaches the receiver module WA-RX-01 Circuit Design. The latter contains a superheterodyne receiver with quartz and SAW filter inserted between the antenna input (pin 6) and the "front-end amplifier (HF) to pass only the single frequency chosen (one of three listed above).
Practically, if the module is tuned to 863.625 MHz, the resonator is also tuned to this value. The filter replaces the varactor tuning circuit to.
The radio frequency signal coming out of SAW between flapping in a blender with that produced by RF local oscillator, quartz and also tuned to a frequency differing from that of SAW antenna of 10.7 MHz. This, of course the value of the MF resulting from the conversion due the beat in the mixer, the difference between the working frequency of the local oscillator and the agreement of the SAW resonator.
The MF is filtered by a ceramic filter to 10.7 MHz, so as to get rid of any parasites, then amplified, filtered again through a second filter to 10.7 MHz, and is then detected by an FM discriminator quartz well.
The audio signal thus obtained, before reaching the pin (1) output goes through an expander dynamics: it is a circuit performing the function parallel to that of the compressor mounted in the transmitter module and used to compensate for the possible attenuation of the signal beyond the threshold level set to avoid saturation.
The expander also has a variable gain amplifier, which it controls to maintain the level of audio output to a predefined value, so if the demodulated AF is too low, it amplifies it and it decreases if it is too strong. The expander provides the audio output signal of constant amplitude, so as to avoid the user of a wireless microphone having to constantly act on the volume control the mixer or amplifier which was connected to the receiver. Using a "buffer", the audio comes out of the expander is routed to pin 1. Note that the module
WA-RX-01 has a muting circuit (muting) internal, used to cut the audio signal output when the received radio signal is too weak to be operated in good conditions, the muffler is based on the level of FM input of the second ceramic filter to 10.7 MHz.
The circuit detects the amplitude of the FM signal and possibly interrupting the audio line driver, using an internal transistor, pin 3: the latter used to light an LED when the receiver has locked onto the frequency of the transmitter.
So if the LED lights is that TX and RX are connected, otherwise the receiver can receive the signal from the transmitter. The signs are useful during the installation of radiomicrophone to control the scope of the system.
Chips Finally a look at the rest of the receptor radiomicrophone: Audio taken from the pin 1 is amplified by operational TL081 voltage mounted non-inverting configuration, whose earnings depend on the position of the slider and the trimmer TR1 may vary between 1 (cursor turned completely to the pin 2) and slightly more than 3 (slider to the output). The amplification is required to raise the level of the audio module outputs WA-RX-01, which normally does not exceed level -10 dBV (about 230 millivolts) to the operational stage is used to lower the output impedance of the receiver module, which is 10 ohms. BM amplified by the TL081 is available between pin 6 and ground: from thence through resistor R5 and the electrolytic C5, it reaches the circuit output, output which can link a table entry mixer and amplifier or recorder audio. Note the resistor R6, used to charge the electrolytic C5 when the circuit is at rest: The purpose of this is to avoid that when the receiver is connected to another audio device, we hear the usual "bump" caused by the impulse derived from the transfer of polarization potential of the output of the operational (exactly half the supply voltage, which makes the bridge R2/R3 ...) when the connection.



Figure 4: Diagram of the receiver.






Figure 5a: Diagram of implantation components of the receiver.

Figure 5b: Drawing scale 1, the circuit board receiver.

Figure 6: Photograph of a prototype of the plate and receiver.

Iist R1 ...... 560 R2 ...... 220 k R3
...... 220 k R4
...... 4.7 k R5 ...... 47 R6 ...... 1 k TR1 ..... 10k trimmer MO / MV C1 ...... 100 nF multilayer C2 ...... 220 uF 16 V electrolytic
C3 ...... 470 nF 63 V polyester
C4 ...... 10 uF 100 V electrolytic C5 ...... 4.7 uF 100 V electrolytic LD1 ..... LED 3 mm green
D1 ...... 1N4007 U1
...... WARX01A
U2 ...... TL081
SW1 ..... slide switch 90 °

Miscellaneous:
a support 2 x 4 1
stereo jack socket for an antenna tuned it
863-865 MHz
taking a 9 V battery
a plastic housing potential

Remember Solder all pins and tabs on the receiver module.



The practical realization of the transmitter and receiver

The practical realization of this radiomicrophone is fairly simple although it must achieve two decks, one for the TX (which involve more or less closely to the microphone itself) and one for the RX (which is placed near the mixer, amplifier or recorder).



Figure 7: The transmitter and receiver modules.





TX.


Module WA-TX-01 is based on an oscillator (stabilized by a SAW resonator) whose frequency can be varied within certain limits, using a frequency modulator to varactor diodes biased by the audio signal level. At the output of the oscillator is an RF amplifier and the output of which was mounted a filter-type antenna low pass to limit the emission of unwanted frequencies. To avoid any phenomenon of overmodulation, the audio signal is processed by a dynamic compressor it is actually an electronic circuit structured to limit the dynamic range, that is to say the trip between minimum and maximum levels of the signal. The module is available in four versions, which distinguishes only the working frequency of the oscillator: 863.125 MHz, 863.625 MHz, 864.5 MHz and 864.875. The transmitted power is 2 mW and stability Frequency is ± 10 kHz; unwanted frequencies emitted in a spectrum of ± 15 kHz about the frequency of oscillation, are maintained at 1 mW. Regarding the audio, the input has an impedance of 5 ohms, and accepts signals whose amplitude lies between -115 and -15 dBu (@ 1 kHz), the compression section of the dynamic pre-emphasis of 50 microseconds. The module requires a supply voltage between 3 and 9 V, it consumes a current of 25 mA. The frequency response ranges from 50 Hz to 15 kHz, which is more than sufficient for most applications (voice and music).

RX.
module WARX-01 is a superheterodyne receiver where the entire floor of agreement is somewhat different from what is typically found: as a fixed frequency, we mounted in series with the antenna input SAW filter tuned to the frequency of the module and not letting it, follows a high-frequency amplifier, whose output is connected to a mixer HF. In the latter part of RF (radio frequency) is mixed with the frequency of local oscillator (quartz, very stable) and we obtain the average frequency equal to 10.7 MHz, prepared by a ceramic filter, then amplified and filtered again through a second filter tuned also on 10.7 MHz. The average frequency is demodulated by a discriminator quartz extract audio, then sent to the expander dynamics and a "buffer" output. The module also includes a level sensor radio signal, taking as reference the average amplitude of the frequency control is a static switch that interrupts the audio line when the RF is too low for quality listening acceptable. This is a "squelch", which cuts the BF if the antenna signal is less than 17 dBmV (RX sensitivity is 21 dBmV). Food is a voltage between 3-12 V (30 mA consumption).


Figure 8: Compress and expanded.
This drawing shows how the "compander" is to say, the compressor and expander ("expander") dynamics of the audio signal: the left section is the process for sending and receiving the right one . As you can see, the transmitter module variable gain amplifier reproduces a wide dynamic range from 0 to -100 dB in the range of 50 dB (-10 to -60 dB): So it compresses a range of 100 dB, reducing it to only 50 dB. This method allows to send signals of high dynamics by modulating the radio carrier while reducing the frequency deviation (or trip, remember that we are on FM). The choice of the compression range is nothing fancy: it was conceived by the designer to keep the weakest signal below the noise threshold determined by the FM signal to the demodulator output at the exit of receiver (-60 dB). On the left side of the drawing we see how the signal remains unchanged when it has a level of -20 dB and is attenuated when other hand is stronger or weaker if it is amplified (eg -100 dB become -60 dB). The compressed audio component is emitted by the TX and received by the antenna RX: there, after demodulation, the expansion takes place through a second variable gain amplifier. In fact the amplitudes up to -10 dB to 0 dB are brought, those from -50 dB to -60 dB, -60 dB to -100 dB. Not remain unchanged as the only signals -20 dB. The first effect of this expansion is that the background noise that appears at the output of FM demodulator with a level of -60 dB (typical), is reduced to -100 dB and becomes almost imperceptible note that the FM noise is of -60 dB, without this operation would expand its presence tedious, which is not the case when it is reduced to -100 dB.

The practical realization of the issuer

The plate consists of a small single sided PCB, which 2b gives a scale drawing. Make it by the method of "blue film" and when it is engraved, drilled and tinned, first insert the jumper J1 (two poles at 2.54), then insert and solder all components (as shown in Figures 2a and 3), continuing with the resistors (mounted upright, folded trombone), capacitors, diode, transistor (in case a half moon), the trimmer and ending with "peripheral" means the jack stand, the slide switch, and decision-9V battery Finally mount the hybrid module transmitter (up to lying, weld pins and securing tabs). Warning orientation of polarized components: diode, transistor and the electrolytic (flat to C6). Place the 9 V battery (watch polarity). A copper wire of 8.5 cm (1 / 4 wave) or 17 cm (half wavelength), welded to the point ANT, is the transmitting antenna. Double check your welds (or short-circuit between tracks or pads or cold weld joints) and identification of components, respect for values, polarities at least twice systematically, you will not regret it because the installation work of the first blow.

The practical realization of the receiver

The deck is also a small printed circuit single sided with 5b gave the drawing to scale 1. Make it by the method of "blue film" and when it is engraved, drilled and tinned, first insert the support of the integrated circuit U2 TL081, then carefully check your welds (or short-circuit between tracks or pads or soldering Cold joints). Insert and then solder all components (as shown in Figures 5a and 6), continuing with resistors, capacitors, trimmer, diode, LED and ending with "peripheral" means the jack stand, the switch fasteners, and decision-9V battery Finally the hybrid module mount receiver (up to lying, solder pins and mounting tabs). Attention to the orientation of polarized components: diode, electrolytics and the integrated circuit (to be installed at the end, keyed reference-oriented U R3). Place the 9 V battery (watch polarity). A copper wire of 8.5 cm or 17 cm, welded point ANT, is the receiving antenna. Check again your welds and the identification of components, respect for values, polarities systematically at least twice, you will not regret not because the installation work the first time. So much for platinum récepteur.Pour TX and RX antennas, you can also use the flexible whip antennas on 868 MHz granted Trade: connect them to the point ANT. Feed the TX with a 9 volt battery 6F22 and install everything (platinum and battery) in the "handle" of the microphone used (kind of micro scene) and then install them in a small box that you slip into your pocket The lavalier microphone is then attached to the collar of the shirt or jacket (if no tie!).
The receiver operates with a voltage between 9 to 12 VDC to be applied to points on 9 V BATTERY, the current consumed is at least 60 mA. Eat it with a 9 V battery (as the issuer) or by a small supply stabilized power supply (this tension may be able to take on the mixer or amp or audio recorder). Besides the plate itself can be incorporated into one of these devices. Do not worry: the receiver module is protected against pests, particularly those from food.



BAND (MHz)


Use



40.980-45 for use Radiomicrophones amateur. 174-223 470-854 Radiomicrophones professional studio and radio broadcasting, recording studio and musical instruments. 862-876 Radio control and wireless audio applications. Currently wireless microphone issue on trade frequency bands allocated by the Ministry in charge of telecommunications for the use of devices short of range, that is to say low-power (usually reserved for communications TX / RX in a studio or an artistic performance, but also used in broadcasting). The table summarizes the frequency bands allowed for this use, for all the transmitter power must not exceed 50 mW. Our radiomicrophone operates in a range between 862 and 876 MHz, for the radio, transmission of data and also to the transmission / reception of audio signals and therefore all-in-fact adapted to the realization of a micro HF. Within this frequency range, our wireless microphone can work through the modules selected from 863 to 865 MHz. You choose what type of microphone if you want hands free. If you want to use a capsule electret preamplified two son, the sending unit can provide the necessary polarization: it is sufficient to close the jumper J1 in order to insert the resistive bridge and apply the bias to the capsule. Taking a microphone or a magnetic electret condense (electret condenser microphone) no fading, the rider will be left open, however: indeed, these microphones require no bias and produce themselves directly an output voltage of electromagnetic origin or piezoelectric.
Radiomicrophones outside professionals.
Figure 9: Frequencies of radiomicrophones (or wireless microphones or wireless microphones).
The choice of microphone Our system can be associated with all types of microphones: the magnetic (there are a few euros) are ideal if you want to keep the microphone in hand (because you want to the tender for a partner or circulate in the room). The capsules are the electret lavalier microphones (tiny microphones mounted on a small alligator clip) the most elegant and most convenient.
trials It remains only to check if everything is okay: Connect the receiver to the mixer or amp, etc.. With a shielded cable terminated with a 3.5mm mono jack (the AUX input of a hi-fi amplifier, for example ...) and, to the jack of the transmitter, insert the microphone jack selected.
Normally the microphones have a 6.35 mm jack, so you should maybe use an adapter from 6.35 to 3.5 mm. Put the cursor trimmers transmitter and receiver half way and lower the volume of the amplifier and then feed the two units, after placing the TX a few meters away from the RX. The receiver LED lights up immediately: this means that the radio link is occurring and that the carrier of the transmitter has a level of listening quality, and if the LED is off, control circuits. Talk
then close to the microphone and verify that the amplifier reproduces the sound of the voice acting needed to adjust the volume of the transmitter (do not produce "feedback") and the receiver gain ( corresponding with the trimmers): turn the cursor clockwise to increase the noise level and vice versa.
Then walk away and check with the TX How far up the LED stays on, to determine the radius range of your wireless microphone system.

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