Wednesday, July 14, 2010

Prepaid Phone Cards

PrePaid Phone cards are a safe and easy way to make a call from almost any phone, anytime, anywhere.Prepaid phone cards originated in Italy back in the mid 1970s and spread from there to the rest of Europe, have now become popular in the United States too. offers a common platform for a wide variety of Prepaid Phone cards online.Save on international calls by purchasing Prepaid phone cards and cheap international calling cards through our website.
Prepaid phone cards represent telephone time you buy in advance. You pay from $5 to $15 or more up-front for local or long-distance phone time; the amount of time you buy depends on the rate-per-minute you're charged.

A prepaid phone card allows you to call almost anywhere from almost any phone simply by dialing a toll-free access number, entering your personal identification number (PIN), and dialing the number you want to reach.

TryCards is dedicated to provide Prepaid phone cards like international prepaid phone cards and rechargeable calling cards with crisp and clear connections . We have tried our best to bring those carriers together that really offer quality prepaid phone cards and that too at reasonable low rates.

Prepaid phone cards have some advantages over credit calling cards. For example, credit calling cards may charge more for your long-distance call at certain times than others, whereas you usually pay a uniform price per minute if you use your prepaid phone card--at least for calls within the U.S. On the other hand, prepaid phone cards (whose per-minute rates, according to one study, varied from 9 to 57 cents) are generally more expensive than making calls from home.

At present we provide access to various Prepaid phone cards that will allow you to make cheap international phone calls to Europe,United States and Asia etc and we make it sure that there are minimal hidden charges.....
Pick the phone card that suits you best like if you prefer low connection rates and no connection charge then opt for US calling card.

Phone cards can be used for multiple phone calls to any and all of available countries. Remember,Our Long Distance calling cards and prepaid phone cards offer the lowest rates for calling to many countries which provide more minutes than ever before with no or low connection fees.

Friday, July 09, 2010

GPS - What Is It?

GPS, or Global Positioning System, is the latest thing in keeping from getting lost when trekking out to visit your Aunt Louise. Years ago you had to rely on landmarks, your handy compass or the guy at the corner gas station, assuming he knew where everything was. Today for about a hundred bucks you can get a little gadget that will tell you exactly where you are, any place on Earth. By using some basic mathematical calculations and a rather complex system, you can be in the middle of the desert, lost as can be, push a button and have your GPS tell you exactly where you are so that you can hopefully find your way back home.

So what exactly is GPS and how does it work?

GPS is actually a very complex and expensive system but the fundamental concepts of the system are very simple.

The GPS system is a group of 27 Earth orbiting satellites. Twenty-four of them are in operation and 3 are backups in case one fails. The system was originally created for the US military but was eventually opened up to everyone else.

Each one of these satellites, weighing in at about 4,000 pounds, circles the Earth at about 12,000 miles per hour and makes 2 complete rotations everyday. The orbits are arranged so that at any one point in the day 4 of these satellites are visible from any place on Earth.

The complimenting receiver that was created to receive signals from these satellites has the job of locating 4 or more of these satellites, figure out the distance to each and from that information determine where on the planet the receiver itself is located. It then transmits this location back to the person who happens to be in possession of the receiver. The operation is based on a simple mathematical principal called trilateration. To simply explain how this works, let's say someone tells you that you are 10 miles from Newark, NJ, another person tells you that you are 15 miles from Maplewood, NJ and a third person tells you that you are 20 miles from Woodbridge, NJ. By taking those three facts you can figure out exactly where you are because each radius of each distance when linked together will intersect at only one point. That point is where you are located.

In order to actually do the calculation from space the GPS receiver needs to know 2 things. The location of at least 3 satellites above you and the distance between you and each of those satellites. The reason that only 3 satellites or spheres are needed is because the Earth itself can act as a fourth sphere. The GPS receiver itself works by radio waves which are a kind of electromagnetic energy and travel at the speed of light The receiver can actually figure out how far the signal has travelled by timing how long it took for the signal to arrive from each of the satellites.

In the next article on GPS we'll go over exactly how this system works to measure distance.

Michael Russell

Thursday, July 08, 2010

Usage of RS 232 in Modern Signalling in Railways

The most popular serial communication standard in use is certainly the EIA / TIA - 232-E specification. This standard which has been developed by electronic industry association and the telecommunication industry association (EIA / TIA) is more popularly referred to simply as RS 232 where RS stands for recommended standard.

RS 232 Specifications

RS 232 is a complete standard. This means that the standard sets out to ensure the compatibility between the host and the peripheral systems by specifying
  • Common voltage and the signal levels
  • Common Pin wiring configurations
  • A minimal amount of control information between the host and the peripheral system
Unlike many standards which simply specify the electrical characteristics of the given interface RS 232, specifies electrical, functional and mechanical characteristics in order to meet the above three criteria. Each of these aspects of RS 232 standard is discussed below.

Electrical Characteristics

The electrical characteristics section of the RS 232 standard includes specifications on the voltage levels, rate of change of signal levels and line impedance. The original RS 232 standard was defined in 1962 as this was before the days of TL logic. It should not be surprising that the standard does not use 5V and ground logic levels. Instead, a high level of driver output is defined as being between -5 and -15 volts. The receiver logic levels were defined to provide a 2V noise margin. As such a high level of the receiver is defined as +3 to +15V and low level is -3 to -15V.

Functional characteristics

Since RS 232 is a complete standard it includes more than just specifications on the electrical characteristics. The second aspect of operation that is covered by the standard concerns the functional characteristics of the interface. These signals are divided into four different categories.

1) Common
2) Data
3) Control
4) Timing

Mechanical Interface characteristics

The third area covered by the RS 232 concerns the mechanical interface. In particular RS 232 specifies a 25 pin connector. This is the minimum connector size that can accommodate all the signals defined in the functional portion of the standard. The connector of the DCE equipment is male for connection housing and female for the connector pins. Likewise, the DTE connector is a female housing with male connection pins. Although RS 232 specifies a 25 position connector, it should be noted that often this connector is not used.

P Praveen

Thursday, July 01, 2010

Cheap Calling Cards For Making International Calls

Due to so many scientific discoveries, people have found several ways of living in comfort. When it comes to the field of communications, a numerous inventions can be named. The major communication barrier was making a call overseas. Calling used to be so problematic to many 50 years ago. It is still prevalent in most of the underdeveloped and the developed nations that do not have the advanced technologies.

However, at present the cheap calling cards have been introduced, making the calling process easier. Calling a different country generally costs a lot, even for a very short time of conversation. Therefore, as the number of family and friends of everybody started increasing, so did the need for making cheaper calls. People became more desperate to find a better alternative to the tiresome trunk call booking. As soon as the cheap calling cards were launched, many people started to use them as they put an end to the highly expensive trunk calls.

In those days, people had to spend so much money on making a call abroad. One of the greatest disadvantages in the traditional method of making calls were the fact that the calls could not be made at once and people need to book for a call beforehand and they had to wait for their turn. Distorted voice and vagueness were created because of the interference due to the analog voice signals. In addition, an unacceptable and intolerable time lag used to be a great nuisance to the people as they had to converse in a stunted manner. People found this to be unsatisfactory as they had pay so more for a vague and paused conversation. The duration of the call generally, used to be very less due to the higher rate it costs per minute. Moreover, the operator who controlled the overseas calls always hears the entire conversation and it was never a very secure or a reliable way to talk about private information. These disadvantages were completely eradicated finally from the cheap calling cards.

As the usage of the internet and the mobile phones are at their highest now, similarly, the cheap calling cards have also taken over the conventional landlines. Many people have given reviews saying that they found it absolutely helpful and comfortable to make the calls to whichever country they want. By adding these cheap calling cards to our lives, it is the most wonderful thing to make international calls. Telephones were used earlier, just to bridge up the gap between two persons but not in an economical way as how the cheap calling cards work.