Amateur Radio Bands Allocations

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Created on Thursday, 20 August 2009 10:42

Last Updated on Monday, 01 April 2013 14:46

Written by Khalid Shoaib AP2MKS

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Popular Bands

So what are the bands that most Radio Amateurs use? The table below shows bands that are relatively common and how and when they are in use. Again your license will determine which bands and what portions you are eligible to use.

* It should be noted that band conditions vary for many reasons and thus all of these bands can at times take on the characteristics of others. See the section on Propagation. This table should be considered a general guideline.

Propagation

When you pick up a handheld transceiver and communicate on VHF or UHF across town or through a repeater you are generally transmitting line of sight. Not so however with HF transmission. When you are using 160m to 10m the signal reaches the earth's ionosphere and bounces back to earth to be received at a greater distance than line of sight.

The Ionosphere

The ionosphere is a layer in the Earth's atmosphere that lies in a range of 80 to 300 miles above the Earth's surface that reflects radio waves. As the sun shines on the ionosphere it changes composition and height which affects the propagation characteristics. In general signals below 30 MHz bounce off this layer and return to Earth while signals above 30 MHz go through the layer into outer space. So watch what you say on 2 meters, someone on Alpha Centauri might be listening. Signals below 30 MHz can also travel by ground wave and be received a short distance from the transmitter.

Daily Patterns

Radio signals that are bounced or refracted off the ionosphere are also affected by the time of day and season of the year. During the 24 hours cycle the ionosphere changes in height above the Earth and bounces some signals while absorbing others. During the day the higher frequencies (above 10Mhz) tend to propagate while lower frequencies are absorbed. At night the reverse happens. There are many exceptions to this but it is a good general guideline.

Seasonal Patterns

Seasons also affect propagation. Summertime in the northern hemisphere means that higher frequencies have better propagation while in the winter the lower frequencies improve. An interesting time of the year for propagation is when the seasons change from fall to winter and from winter to spring. This is often when the best DX can be found.  Because the seasonal change is occurring in both hemispheres but in the opposite direction DX from North American to Australia or southern Africa can be at its best.

The Sunspot Cycle

Another phenomenon that affects radio propagation is the 11 year sunspot cycle. A peak occurred during the year 2000 and the next peak will occur around 2011. A sunspot low occurs at the midpoint of this cycle. When the sunspots are at their maximum propagation is at its best. At this time the higher shortwave frequencies exhibit the best propagation extending to 6 meters which becomes quite popular during this time of the cycle. 10 meters can easily work stations worldwide with low power (even qrp) and a modest antenna.

Making Propagation Work for You

VHF and UHF

Although these frequencies are not normally thought to be bands where propagation occurs there are times when it signals on VHF and UHF travel well beyond their expected distance. These conditions generally occur erratically and are not as predictable as HF conditions. Some of the conditions that can affect VHF and UHF are:

• Tropo - This condition refers to tropospheric propagation which is primarily affected by weather systems. Look for significant weather changes such as a cold front moving in or a major storm system. Also early evening as the earth cools and early mornings as the earth warms can cause these conditions.
• Sporadic E - occurs when small patches of the ionosphere are ionized . Sporadic E occurs during June-July and early August and again in December and January. as the name suggests this condition is sporadic and you have to be very patient to benefit from it.
• Aurora - The northern lights (aurora borealis) occurs in the northern parts of Canada and can also be seen from northern U.S. states. The "lights" are caused by a solar storm and can have an effect on radio propagation. If can affect VHF and UHF as well as HF propagation. To use the aurora you may need to point your antenna north to work a station to the south as signals bounce back from the aurora.

Depending on who you want to work and where the operating mode you choose can be almost as important as the propagation. The section Operating Modes explains the various modes that you can choose from as a radio amateur.

Operating Modes

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.

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.

Digital Modes

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:

• RTTY - 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 error-free.

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.

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 taking to hams many thousands of miles away with the signal quality of a local contact.

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 on IRLP

Summary

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.

Courtesy : eham.net