Listening to amateur radio transmissions on a radio scanner is easy as there are so many places in the radio spectrum where amateurs are allowed to operate.
In this article we are going to show you where you can hear amateur signals and explain some of the systems that radio amateurs use for their hobby.
Amateurs use many different modes when sending out signals from FM (Frequency Modulation) through all the AM (Amplitude Modulation) types and a huge amount of digital data modes that require computer software to decode them but we will be dealing only with the FM signals here as these can easily be picked up on almost every scanner you can buy today.
Amateur Bands Overview
As FM is rarely used on frequencies below the 50MHz amateur band those frequencies are not listed here.
50-54 MHz (6 Meters)
70-70.7 MHz (4 Meters)
144-148 MHz (2 Meters)
420-450 MHz (70 Centimeters)
Not all frequencies are open to all amateurs with this depending on where in the world you are. There are 3 separate areas which are called ITU regions (International Telecommunication Union).
Region 1. 50-52MHz, 70-70.5 MHz, 144-146MHz, 430-440MHz,
Region 2. 50-54MHz, 144-148MHz, 420-450MHz
Region 3. 50-54MHz, 144-148MHz, 420-450MHz
Amateur repeater frequencies can be different for each country depending what has been decided by the individual countries agency for control of the radio spectrum but repeaters are generally located towards the top end of each band allocation. For an up to date listing of these frequencies you can search online for the amateur radio association from your country and look for a band plan on their website.
The inputs and outputs on amateur repeaters are on different frequencies and to successfully listen to what is being said on the repeater its best to listen to the outputs, you may receive something on the inputs if the transmission is local or you are located up high.
To list complicated frequency information here would mean it will go out of date very quickly as changes are being made to every countries amateur band plan all the time.
There are a more amateur band allocations stretching all the way up into the microwave bands but the range of these transmissions is shorter with more specialized equipment needed to receive signals and they lack the use that the “core” amateur VHF and UHF frequencies listed above enjoy.
How the Amateur Repeater System Works
Under normal conditions all transmissions in the VHF/UHF amateur bands work on a line of sight principle meaning that both stations wishing to communicate must be able to “see” each other. The one advantage to have if you are transmitting at these frequencies is height giving you a longer range on your signal before other hills, mountains or the natural curvature of the earth blocks your transmissions to the receiving station.
Amateurs get around the disadvantages of working at these frequencies by a using a network of repeaters located on very high points that can transmit over a very wide area.
Basic repeater operation is as follows….
- Mobile 1 transmits on the input to the repeater sending a short tone burst to “open” the repeater for use (the tone burst is to stop unwanted signals activating the repeater).
- Mobile 2 picks up the signal from Mobile 1 that is transmitted on the output of the repeater and they start a conversion with all signals going through the repeater.
This type of repeater operates in what is called “duplex mode” where it uses one frequency for receiving and another for transmitting.
If you look at the diagram you will notice that without the use of the repeater there is no possibility of either of these mobile stations ever being able to talk to each directly. When listening to amateur signals through a repeater you don’t need to receive any of the mobile stations directly on your radio scanner as both sides of the conversation will be rebroadcast by the amateur repeater.
When a repeater is not in use it will transmit a short burst of Morse code about every 15 minutes to identify itself and letting anybody listening know that its is operational.
This system of helping people communicate of greater distances is employed across private two way radio networks everywhere from taxis to police and army transmissions.
How the Amateur Simplex Channels Work
Simplex operation is the traditional way that two way radios communicate without the use of a repeater to extend the range of the signal. For 2 stations to talk to each other they must transmit directly to each other meaning they must be closer to each other than if working throw a repeater.
Transmissions on simplex channels can be hard to receive unless they are close of you have the advantage of lots of height, taking a radio scanner up a high mountain will reveal signals from over a wide area and is well worth the effort just to see how far VHF/UHF transmissions can travel at line of sight.
Next time we will show you how to decode some of the data transmissions on the VHF/UHF amateur bands with some free software and a basic computer.
ITU region grahic courtesy Wikipedia