What is SSB Radio?
‘SSB stands for ‘single side band’ but actually isn’t really a band at all. SSB is properly referred to as a mode much like AM or FM
SSB is a very efficient way of capturing your voice into a radio wave and the transmission of that radio wave as a signal.
The process of applying a voice to a radio wave is referred to as modulation. So to modulate a radio wave is to add information to it so that can be received. In most cases this will be in the form of the sound of a voice.
Most people are familiar with the most common forms of modulation, AM (amplitude modulation), and FM, (frequency modulation), giving the AM and FM bands their common name.
You will probably have used FM or AM in the form of children’s walkie talkies or remote control toys like toy cars or planes.
When in AM mode, your voice modulates, (is superimposed), on to a carrier wave at a specified frequency by your transceiver and is transmitted over the air waves.
The carrier wave is used to “carry” the audio information to an AM receiver where it is detected and transformed back into an audio signal allowing the voice message sent to be understood.
In an AM modulated radio signal, the carrier, is continuously transmitted. Due to the nature of the way AM is produced in the transmitter, two identical modulating signals are attached to the carrier wave, these are known as the ‘sidebands’.
Any audio that you hear on an AM receiver is from the two sidebands. When the radio transmitter you are tuned to is not transmitting any sound, you can still hear something and will register a reading on your signal meter.
These two modulating (audio) sidebands are located on either side of the carrier wave, one just above it and the other just below. The audio sidebands that form an AM broadcast signal are quite important. They contain the “information or audio” intended for the receive station.
Although AM radios have been used for decades it was found that an AM signal can be modified to produce improved results.
A number of differing methods were developed using the sidebands without a carrier wave by utilising special circuits in the transmitter. This allows the modulation to remain without the need for a carrier.
This is known as double sideband (DSB) and was typically used in the early experiments because it was much easier to filter out just the carrier than to filter out the carrier and one of the sidebands.
In later developments it became possible to filter out the carrier and either of the sidebands giving us single side band. Radio equipment with the appropriate circuits and filters can receive transmissions that can be either lower sideband (LSB) or upper sideband (USB). If you listen to an SSB signals the voices are altered and can be very muffled and distorted and can sound ‘Donald Duck’ like when not fully tuned.
Since you still require a carrier to ‘demodulate’ a signal, you need a SSB Radio to listen to these transmissions.
This is achieved in a SSB receiver by circuits that inserts a very low level carrier wave back into the receiver with the lower or upper sideband signal and the audio that was transmitted is restored in the receiver with almost identical reproduction of the original voice. The SSB receiver needs to be finely tuned to make the voices sound natural. If you adjust the tuning of the radio tuned off of the transmitter frequency, the voices will be higher or lower pitched, resulting in that “Donald Duck” sound.
With practice it becomes easier to fine tune the radio until the voice sounds more “natural”. Your receiver must be in the same “mode” as the transmitted signal or this process does not work. If the transmitter of the other station is in the USB mode, your receiver must be in USB mode and vice versa.
Since the fidelity of the SSB voice transmission has been altered somewhat through the various filters in the process usually only the most important portions or characteristics of the voice frequencies are allowed through, and this causes the lack of fidelity to the transmission, and only the portions of the voice characteristics remain, which is all that is needed in the first place. It is a “communications” mode, not wide band HI FI commercial broadcast FM radio.
The information contained in the average human voice needed to understand the voice is contained within about the first 3000Hz of the human hearing range. Frequencies of the human voice beyond this range are not needed for communication purposes and are filtered out in the modulation process. So the average bandwidth of a SSB signal is about 3000Hz wide with all of the voice characteristics needed within that range to be understandable.
Back to AM for a bit. When producing that AM signal we were talking about, the end result is that approximately half of the transmitter power is “wasted” on the carrier and the rest of the power is divided between the two sidebands. As a result, the actual audio output from a 1000 watt AM transmitter (500 watts of carrier + 250 watts on each sideband) would be the same as a 250 watt SSB transmitter in its effectiveness. So in effect, that is a 4 to 1 ratio. As only one sideband is transmitted and received, the receiver’s needed bandwidth is reduced by one half, effectively reducing the required power by the transmitter another 50%
So, in theory, the ratio has now doubled from 4 to 1 to become 8 to 1! For example,
a ham radio station running 1000 Watts AM, would sound no better than another ham running 125 Watts PEP (Peak Envelope Power) on SSB!!!
We have learned that it would take 1000 watts of AM to be as effective as 125 watts SSB. This is an 8 to 1 radio. The reason for the efficiency of SSB, is that all of the power used to produce both sidebands and the carrier (1000 watts AM), are now used in only one sideband at the transmitter, and when you account for the receiver re-adding only a very, very tiny portion of that power back into the equation, you are increasing the efficiency about 8 times better than a standard AM transmitter! This is one reason why long distances can be covered effectively with SSB using much less power than AM.
When you are in either sideband mode, listening to the background noise and all of a sudden you hear a tone in the background, you are hearing the “carrier” that is being re-inserted in your receiver beating against the carrier of another station that is transmitting no information on his carrier and this produces a different frequency if he is slightly off of the frequency you are tuned to.
If you tune your receiver to exactly his transmit frequency, the tone will disappear because the difference in frequency between your receiver and his transmit frequency are so close that you can not hear the low audio frequency.
Also, when you key your mic and are in SSB mode, look at your watt meter and you will see no power being output. Remember that there is no carrier produced in the transmitter when using the sideband mode so no carrier will be registered on the meter. If you scratch your finger across the face of the mic or speak into it, you will then see the meter register the “modulation”.
The instant you “modulate” the transmitter with your voice, you will see that the meter shows that now you have output. Many new radio users to SSB seem to forget that they are not transmitting a carrier when they key their mic with no modulation. So remember that when checking swr, you MUST have your transmitter in the AM or DM mode with the transmitter keyed up in order for the swr meter to detect the signal!
You CAN NOT CHECK SWR IN ANY SSB MODE!
Now that you have learned more about how SSB works just remember that the SSB mode of transmission is the predominant mode of transmission used by most radio ham to effectively and efficiently work the world!