There are two common methods of producing a pseudo stereo effect from a mono signal, playing the mono signal from the two speakers in antiphase, and the use of frequency selective techniques which normally consists of directing lower frequency signals into one channel and higher fre­quency signals into the other. This circuit uses the second technique, but can additionally give antiphase signals which can give a better effect, especially when using headphones.

stereo_synthesizer

Q1 is used as an emitter fol­lower buffer stage which ensures that the two filter networks fens from its output are driven from a low impedance source. If these were driven direct from the input, it is quite possible that they would be fed from a source impedance of a few kilo ohms or more, which would be quite sufficient to alter their effective characteristics.

The two filters are formed by R4 and C3 (low pass), and C6 plus R8 (high pass). A high roll off rate is by no means essential in this application and the 6dB per octave attenuation rate of simple RC filt­ers such as these is perfectly ade­quate. The -3dB point of each filter is at approximately 800Hz and the combined output of the filters, therefore, gives a virtually flat res­ponse with no significant peaks or troughs.

Q2 is connected as an emitter follower buffer stage and this ensures that there is minimal loading on the low pass filter. Q3 similarly ensures that there is minimal load­ing on the high pass filter, but this device is also used as a phase splitter. With SW2 switched to take the output from Q3’s emitter, Q3 effectively operates as an emit­ter follower and gives no phase inversion. With SW2 switched to take the output from Q3’s col­lector, Q3 then effectively acts as a common emitter stage with 100% negative feedback (and unity voltage gain) due to R11. 1t also provides a 180° phase shift so that the two output signals are in anti-phase. An in-phase relationship is needed to give a good central ste­reo image and the use of anti-phase signals tends to give an im­pression of increased channel separation.

In a stereo orchestral recording, it is normal for the violins to come from the left hand channel, with the cellos and basses from the right hand channel. Therefore, the high frequency signals are fed to the left channel and the low fre­quency signals are fed to the right channel so that the unit provides a similar effect (although it will ob­viously function properly with the outputs connected either way).

Wireless communication has experienced tremendous growth in the last decade. High data rate wireless communication is becoming increasingly important to mobile users in corporate and public networks in the indoor environment. Although voice and low data rate services were the first applications of cellular networks, the focus in recent years has shifted to very high-bandwidth delivery, which is a key driver for system and network design. While wireless local area (WLAN) access is important for data applications, mobile users still expect reliable GSM and 3G coverage for their voice service and seamless transition as they move indoors from an outdoor environment. Research shows that 75% of all mobile calls originate inside buildings at work, home or public places. This has in turn led to consumer awareness and expectation of ubiquitous coverage, and the ability to use their wireless devices anywhere.

 Relying on the penetration of the GSM and 3G radio signals from the outside for providing in-building coverage is neither practical nor reliable in many buildings, and additional indoor antenna units (AUs) must be installed. Different building shapes and materials such as steel and metalized glass, cause in-building penetration of radio frequency (RF) signals to weaken resulting in reduced data rates and even complete loss of signal. This will become even more apparent over the next few years with the introduction of new 4G technologies which require considerably higher signal integrity and radio frequency than their voice counterpart. Also, with the trend to increasing data rates on wireless networks and a rapidly increasing number of users who want un-tethered access pose new challenges to system integrators and network designers. This results in significant challenges for the wired infrastructure that is required to connect the numerous antennas units.

 Wireless over fibre (WoF) systems which also known as Radio over Fibre (RoF) systems have attracted much interest for broadband wireless access, offering a simplified  overall system design due to the aggregation of RF signal generation and network management at a central location. Distributing broadband wireless signals over optical fibre has a number of advantages compared with traditional copper cabling. The wide bandwidth of optical fibre further allows different services such as Gigabit Ethernet, IEEE802.11a/g, GSM and 3G to share the same infrastructure, making the wireless-over-fibre approach a truly multi-operator and multiservice technology.

WLANs have had a profound impact on our perception of communication. First of all, the vast majority of users now believe in the new notion of “always on” communication. We are now living in the era of ubiquitous connectivity or “communication anytime, anywhere, and with anything”. Secondly, the concept of broadband communication has caught on very well. As fibre penetrates closer to the end-user environment (Fibre to the Home/Curb/X, FTTH/C/X), wired transmission speeds will continue to rise. Transmission speeds such at 100 Mbps (Fast Ethernet) are now beginning to reach homes. The demand to have this broadband capacity also wirelessly has put pressure on wireless communication systems to increase both their transmission capacity, as well as their coverage.

Figure 1: PRESENT COMMUNICATION SYSTEMS

In general there is a trade off between coverage and capacity. Figure 1 shows the relationship between some of the various standards (present) in terms of mobility (coverage), and capacity. For instance, the cell size of Wireless Personal Area Networks (WPANs) is typically a few metres (picocell), while their transmission rates may reach several tens of Mbps. On the other hand 2G (e.g. GSM), and 3G (e.g. Universal Mobile Telecommunication System (UMTS) and the International Mobile Telecommunications (IMT2000)) systems have cells that extend several kilometres, but have data rates limited to less than 2 Mbps. Therefore, as mobile communication systems seek to increase capacity, and wireless data systems seek to increase coverage, they will both move towards convergence. A case in point is the IEEE 802.16, otherwise known as WiMAX, which appears to lend weight to the notion of convergence, as shown in Figure 1 WiMAX   seeks  to  provide  high-bit  rate mobile services  using  frequencies  between      2-11 GHz. In addition, WiMAX also aims to provide Fixed Wireless Access (FWA) at bit-rates in the excess of 100 Mbps and at higher frequencies between 10 – 66 GHz.

Toshiba Satellite L300

Sometimes we get a notebook that packs so much punch into an affordable platform that makes us wake up and actually take notice. And this is the case with Toshiba Satellite L300D – 01N Laptop computer. Big name but small price!

This Satellite L300 laptop from Toshiba is well within an affordable price range, but it still packs all the useful components you need to get your life fun around.

What it has is Dual Core processing, Wireless connectivity and much more.

Processor

Toshiba Satellite L300 runs on AMD Athlon 64X2 Dual-Core QL-60 1.9 Ghz Processor. This CPU gives you processing speeds of 1.9 Ghz per core.

Memory

AMD Athlon 64X2 Dual-Core QL-60 1.9 Ghz Processor of Toshiba Satellite L300 is backed up by 2GB of DDR2 memory. This will knock out memory hungry applications easily. As well as making multi tasking operations.
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Mobile phones have become an integral part of our life. It has influenced our lives in such a way that we cannot even live without mobile phones. Since it is a battery operated device, we expect maximum hours of operation after a battery recharge. You can make sure that your mobile phone will not become dead due to low battery, if you follow the simple steps furnished below.

One of the major causes for sudden battery drain is nothing other than playing games. This fact might make you unhappy, but if you are going to a place where there is not facility to charge your mobile phone you can think of not playing games.

If you are sure that you are not going to make any calls and there is no chance for an incoming call, then switch off your mobile phone without a second thought. Thing is that, we usually keep our phones in our coat or bag in the switched on state, even when we are sure that we don’t need mobile phones for a specific time period.

If you are in an area of weak signal strength, more battery charge will be utilized, while your mobile phone searches for signal. So you can think of switching off your mobile phone if you are sure that you will be in an area of weak signal strength for a long period of time. At the same time less battery charge is used when your mobile phone searches in a strong signal condition.

You can get more out of your mobile phone battery if you turn off the backlight and vibrate function. Ringing takes less power as compared to vibrate function.

Limited net surfing can save battery charge. Sensible use of Bluetooth will definitely help you to save battery charge.

The information signal should be converted into electronic signals, when free space is the channel. Such signal consists of both electric and magnetic fields. The so-called electromagnetic signals are also referred to as radio frequency (RF) waves.
RF waves oscillate i.e., amplitude of the electric and magnetic fields vary at the specific rate. These oscillations may occur at a very low frequency or at an extremely high frequency. This entire range of frequency is the electromagnetic spectrum. Electromagnetic radiation has an electric field and magnetic field which oscillate in phase perpendicular to each other and to the direction of propagation. Radio frequency band is the frequency or the rate of oscillation within the range of about 3Hz to 300GHz.

The frequency spectrum extends from subsonic frequencies (a few hertz) to cosmic rays (1022Hz). The International Radio Consultative Committee (CCIR) bands are given below.

Extremely low frequency (ELF) :

ELF range varies from 30Hz to 300Hz and includes ac power signals and low frequency telemetry signals.

Voice frequencies (VFs) :

VF range varies from 300Hz to 3000Hz. Standard telephone channels has 300Hz to 3000Hz bandwidth.

Very low frequency(VLF) :

VLF range varies from 3 KHz to 30 KHz, which includes the upper end of human hearing range. They are used in sub-marine applications.

Low frequency (LF):

LF range varies from 30 KHz to 300 KHz and is used in marine and aeronautical navigation.

Medium frequency(MF):

MF range varies from 300 KHz to 3 MHz and is used for commercial AM broadcasting (535 KHz to 1605 KHz).

High frequency(HF):

HF ranges vary from 3 MHz to 30 MHz and are called short waves. Most of the two-way communications use this range. Amateur radio and citizen band radio also use signals in this range.

Very high frequency (VHF):

VHF range is from 30 MHz to 300 MHz, these are used for mobile, radio, marine, aeronautical communications, commercial FM broadcasting (88 MHz to 108 MHz ) and commercial TV broadcasting (54 MHz to 216 MHz)- channels (2-13).

Ultra high frequency(UHF):

UHF range is from 300 MHz to 3 GHz. It is used for commercial TV broadcasting of channels 14-83, land mobile communication, cellular phones military services, certain radar and navigation systems, microwave and satellite radio systems. Frequencies above 1 GHz are microwaves.

Super high frequency(SHF):

SHF range varies from 3 GHz to 30 GHz and is used in microwave and satellite communication.

Extremely high frequency (EHF):

EHF range varies from 30 GHz to 300 GHz.