Amateurs radio operators have a variety of modes to choose
from when engaged in two way communication. A mode refers
to the way the signal is modulated during transmission.
Commonly used forms of modulation are AM, FM, SSB, and
digital. In order for a signal to be transmitted and
received in a readable manner it is modulated
electronically. Both transmitter and receiver must be
using the same form of modulation for the communication to
be successful. Each of these modes will be discussed
below. The table of preferred modes for voice
communication gives some idea of what to expect when you
use a particular band. Some modes such as Rtty use LSB for
The following voice
modes are used by general agreement.
15, 12, 10 meters
||2, 1.25 m
and 70 cm. Some USB is also used.
Each mode has its own unique characteristics. One of these is
amount of bandwidth occupied by the signal. CW is quite narrow
(less than 250 Hz) while FM is rather wide (15-20 kHz). A
narrower signal means there is room for more signals and thus
more activity on the band. On the other hand a narrow signal
transmits less quality or information. CW requires the use of
Morse code whereas FM results in a high quality signal for voice
communication. In the following each of the more widely used
modes is discussed briefly.
(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
(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 (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 (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.
Digital modes have been around since RTTY but really took off
with the computer generation. To oversimplify digital modes use
the off-on (binary 0-1) to send information. CW is really a form
of this although quite rudimentary. Most digital modes require a
computer to be interfaced with the radio to assist with sending
and receiving the data. Most also require a TNC (terminal node
controller) with a chip that supports the particular mode. You
send by tying on a keyboard and receive by viewing the
information received on the screen. Some of the more popular
digital modes are:
- Radioteletype (RTTY) uses a baudot (5 bits per character)
or ASCII code (7 bits per character) to communicate. RTTY is
almost as reliable as CW and there are many hams who use
this mode on a regular basis on the HF bands.
- Packet - uses the complete ASCII
character set which permits both upper- and lowercase
characters in a transmission. Packet is error-free which is
achieved by sending data in small packets with a check bit.
If an error is detected by the receiving station it replies
and requests that the packet be resent. This is repeated as
needed to receive the packet correctly. When signals are
good a packet rarely needs to be sent twice but under poor
conditions the resending of error packets slows down the
exchange of information.
- Tor Modes - TOR means
"teleprinting over radio." These modes include
AMTOR, Pactor, G-TOR and Clover. Basically they all use some
variation of the technique mentioned in packet for ensuring
error-free transmission. Each use specialized algorithms for
transmission resulting in improved speed and accuracy.
- PSK-31 - is a relative newcomer to the
digital scene and is fast becoming a primary digital mode.
One reason for its appeal is that it uses the sound card in
the computer to send and receive through the radio. No other
special equipment is needed. PSK-31 uses very little
bandwidth, less than CW and can function very well at low
signal strengths. Unlike Packet and TOR it is not
FSTV and SSTV
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.
(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 taking 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. Be sure to see David Cameron
VE7LTD's excellent website for more detail.
Want More? See Paul's (VE3SY) full article
This has been a brief introduction to the modes you
will encounter in Amateur Radio. For more detail the ARRL
Handbook is an excellent resource as are many of the web sites
devoted to Amateur Radio. Once you have chosen your mode
consider the many Amateur Activities to
choose from. Or maybe its the other away around--choose your
activity and then your mode. Either way you are sure to enjoy
what is to come.
© 2001 - 2007 Don Cassel VE3XD