Saturday, July 21, 2012

What is Amateurs Radio??

If you were to ask a dozen different amateurs what ham radio meant to them chances are you would get 12 different answers. Radio amateurs have discovered a richly rewarding high-tech hobby that has many different appeals to different people. Whether it is the ability to talk to local friends over the radio waves using a hand-held transceiver (HT), communicating digitally with packet radio to exchange personal messages or vital information in an emergency, talking to other hams anywhere in the world, or engaging in contests with other Radio Amateurs over the airwaves there is something for everyone. The section What Hams Do gets into more detail about these activities.

Amateurs or Hams?

Amateurs are often affectionately called hams or ham radio operators and frequently the public is more familiar with this term than with the legal term Radio Amateur. The source of the name ham is not known but it has been around almost from the beginning of amateur radio radio in the early 1900s. The name amateur has nothing to do with skill or knowledge but rather implies that ham radio cannot be used for commercial or revenue generating purposes. It is truly a hobby but often one that makes a difference especially in emergency or disaster situations.

Modes of Communication

Amateur radio operators generally use radio transmitters and receivers to communicate with each other. As you will discover in these pages there are many forms of communication although voice (also known as phone) is still the most widely used. Some of the other forms of transmission are Radioteletype (Rtty), Morse code (CW), television, and digital modes such as Packet, Pactor and PSK-31. A recent survey shows that phone is the most widely used with CW standing second.

Getting Licensed

To become a radio amateur you will need to get a license. Licensing requirements are different in every country with different rules, privileges, and classes of license. The section How to Become a Radio Amateur gives some direction on this from the Canadian and U.S. perspective. Basically different levels of license gives different privileges on the ham bands. The more challenging the license requirements the more privileges that are granted and the more interesting and enjoyable ham radio becomes.

Saturday, July 12, 2008

Radio horizon

In telecommunication, radio horizon is the locus of points at which direct rays from an antenna are tangential to the surface of the Earth. If the Earth were a perfect sphere and there were no atmospheric anomalies, the radio horizon would be a circle. To compute the radius of the circle drawn on the earth in such a case use the formula:

\mathrm{horizon}_\mathrm{miles} = 1.23 \times \sqrt{\mathrm{height}_\mathrm{feet}}.

This is the geometric straight line of sight horizon. For an equivalent formula for an antenna height in metres and a radio horizon in kilometres would be

\mathrm{horizon}_\mathrm{km} = 3.569 \times \sqrt{\mathrm{height}_\mathrm{metres}}.

These formulas are approximations for the case that the height is much smaller than the earth radius. The precise formula is

\mathrm{horizon} = \sqrt{2 r h + h^2}

where r is the earth radius and h the height.

The radio horizon of the transmitting and receiving antennas can be added together to increase the effective communication range.

Antenna heights above 1 million feet (1966 miles, or 3157 kilometres) will cover the entire hemisphere and not increase the radio horizon.

VHF and UHF radio signals will bend slightly toward the earth's surface. This bending effectively increases the radio horizon and therefore slightly increases the formula constant. The ARRL Antenna Book gives a constant of 1.415 for the feet/miles formula for weak signals during normal tropospheric conditions. This can usefully be approximated as:

\mathrm{horizon}_\mathrm{miles} = \sqrt{2 \times \mathrm{height}_\mathrm{feet}}.

In practice, radio wave propagation is affected by atmospheric conditions, ionospheric absorption, and the presence of obstructions, for example mountains or trees. The simple formula above gives a best-case approximation of the maximum propagation distance but is not sufficiently adequate for determining the quality of service at any location.

From Wikipedia, the free encyclopedia

Wednesday, December 26, 2007


How its start.

Its begin when i accidentlty read a books regarding radio. I still remember the tagline on one of the chepter 'In radio or wireless comunications, a transmitter converts data into electromagnatic (EM) waves intend for recovery by one or more receivers'. After finish its me really getting aquainted with ham radio.