VARIOUS OPERATING MODES
PACKET RADIO
Packet radio is a particular digital mode of Amateur Radio ("Ham" Radio) communications which corresponds to computer telecommunications. The telephone modem is replaced by a "magic" box called a terminal node controller (TNC); the telephone is replaced by an amateur radio transceiver, and the phone system is replaced by the "free" amateur radio waves. Packet radio takes any data stream sent from a computer and sends that via radio to another amateur radio station similarly equipped. Packet radio is so named because it sends the data in small bursts, or packets.
IRLP
IRLP (Internet Radio Linking Project) is a method of linking the Internet with Amateur Radio. Usually the link is made through a local repeater so you can connect to someone with a handheld. Basically you sign on to the local repeater and enter a code to connect you to the Internet link. From there you are connected to other repeaters who are also on the Internet. So with your handheld you can be talking to hams many thousands of miles away with the signal quality of a local contact. IRLP is a Canadian invention by VE7LTD and uses Voice over IP (VoIP) to instantly interconnect one or more repeaters around the world. Now with your basic license new radio amateurs are able to use an HT to communicate worldwide. The aim of the Internet Radio Linking Project (IRLP) is to provide a simple and easy system to link radio systems together using the Internet as the communications backbone. This allows hams from all around the world to talk to one another without relying on radio conditions.
CW
CW (continuous wave) is a simple unmodulated signal unlike others which use some form of modulation. By interrupting the signal with a key, Morse code is sent. Thus Morse code is not a mode but, as the name implies, a code which is used to communicate by controlling the CW signal. Although it takes some time and practice to become proficient with the code using CW is one of the most reliable forms of communication as it can generally make it through the most difficult conditions where other signals can't.
AM
AM (amplitude modulation) was the early mode used by hams for voice transmission. In AM the signal is a carrier (like CW) that has upper and lower sidebands that are modulated by varying the amplitude (strength) of the signal. Most shortwave broadcast stations use this method. If you tune to the BBC or some such station using either USB or LSB on your receiver you can hear the carrier as a continuous tone as you move slightly away from the center of the signal. If you listen around the upper end of the 80 meter band you may find some hams using this mode. However AM takes twice the bandwidth of SSB and so is not widely used in Amateur radio.
SSB
SSB (single sideband) is a mode where the carrier and one sideband of the AM mode has been suppressed. Whether using USB (upper sideband) or LSB (lower sideband) more of the transmitter's signal is focused in the sideband used as compared to AM. As a result the signal travels farther and is easier to copy under many unfavourable conditions. SSB is the phone mode of choice for Amateurs on the HF bands.
FM
FM (frequency modulation) is what you hear on 2 meters when using a handheld and working through the club repeater. It is the mode where most hams begin. FM has exceptional quality for voice communication and there is generally no noise or fading that you hear on HF with SSB or CW. However because of its wide bandwidth requirements it is usually limited to bands such as 2m or 70cm where there is lots of room. Some FM can also be heard on 10 meters around 29 MHz.
FSTV and SSTV
Fast scan TV (FSTV) and slow scan TV (SSTV) are modes used to send pictures or images over the radio. SSTV is generally used on the HF bands and can only send a still picture due to its low data rate and bandwidth. FSTV on the other hand is generally used on the UHF bands and can send a moving picture. Recently several HT manufacturers have produced handheld radios with built-in cameras and screens for use in this mode.