Post by Radio Administrator on Feb 4, 2005 10:16:02 GMT
Although Sideband is illegal for use on UK CB, the RA are said to be "considering" or "testing" the use of SSB for use with UK CB. Also, there are many discussions about the subject. This page was added so that CBers may understand the technical side and why people may want it.
This page is NOT intended to encourage the use of an illegal mode, just to explain the technical side.
The following information and graphics are taken from the radio and electronics site (see link at page bottom).
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Sidebands are the two sets of frequencies created when a carrier is modulated. These two bands of frequencies lie just above the carrier frequency (USB), and just below the carrier frequency (LSB).
For a carrier being amplitude modulated by a single frequency, there will be just two side frequencies...
Carrier + modulating frequency, and carrier - modulating frequency.
As a single sideband signal uses no carrier, and just one of the sidebands, this mode is very efficient, and greater distances can be achieved with the same power output. As the required bandwidth is equal to the bandwidth of the modulating signal (1/2 that of AM), this is also efficient on band space.
SSB Transmission.
To transmit a single sideband (SSB) signal, first the carrier is removed to give a double sideband, suppressed carrier signal. This is done using a balanced modulator.
The next stage is to remove either the upper or lower sideband, to give a single sideband signal. This is achieved with the use of a narrow crystal filter.
The output stages in an SSB transmitter must be biased to class AB.
SSB Reception.
To select one sideband for reception, a narrow crystal filter is used, but to demodulate a signal, a carrier is required. As a sideband signal does not include the carrier, a carrier is created and inserted by the receiver. The frequency of the inserted carrier must be very accurate, as any error causes distortion.
Selecting one sideband.
This can be achieved with just one filter on a fixed frequency...
First let us look at a filter being used for AM or FM. The carrier frequency is set to the centre of the filter bandwidth, where attenuation is equal above and below the carrier, and so for each sideband.
The carrier, and both sidebands will pass through the filter.
Now look at a filter being used for upper sideband. The carrier frequency set to the bottom edge of the filter passband.
The lower sideband will be blocked by the filter, but the upper sideband will pass through.
As the carrier oscillator has been shifted down, the VCO will need to be shifted UP by the same amount so that the output is still on the correct frequency.
Now this same filter is being used for lower sideband. The carrier frequency set to the top edge of the filter passband.
The lower sideband will now pass through the filter, but the upper sideband will now be blocked.
As the carrier oscillator has been shifted up, the VCO will need to be shifted down by the same amount so that the output is still on the correct frequency.
The filter used for SSB signals only needs to be as wide as the modulating bandwidth. For communications equipment, this is usually no more than 3KHZ.
As the bandwidth of AM and FM signals is much higher, a separate, wider filter needs to be used for these modes.
This page is NOT intended to encourage the use of an illegal mode, just to explain the technical side.
The following information and graphics are taken from the radio and electronics site (see link at page bottom).
--------------------------------------------------------------------------------
Sidebands are the two sets of frequencies created when a carrier is modulated. These two bands of frequencies lie just above the carrier frequency (USB), and just below the carrier frequency (LSB).
For a carrier being amplitude modulated by a single frequency, there will be just two side frequencies...
Carrier + modulating frequency, and carrier - modulating frequency.
As a single sideband signal uses no carrier, and just one of the sidebands, this mode is very efficient, and greater distances can be achieved with the same power output. As the required bandwidth is equal to the bandwidth of the modulating signal (1/2 that of AM), this is also efficient on band space.
SSB Transmission.
To transmit a single sideband (SSB) signal, first the carrier is removed to give a double sideband, suppressed carrier signal. This is done using a balanced modulator.
The next stage is to remove either the upper or lower sideband, to give a single sideband signal. This is achieved with the use of a narrow crystal filter.
The output stages in an SSB transmitter must be biased to class AB.
SSB Reception.
To select one sideband for reception, a narrow crystal filter is used, but to demodulate a signal, a carrier is required. As a sideband signal does not include the carrier, a carrier is created and inserted by the receiver. The frequency of the inserted carrier must be very accurate, as any error causes distortion.
Selecting one sideband.
This can be achieved with just one filter on a fixed frequency...
First let us look at a filter being used for AM or FM. The carrier frequency is set to the centre of the filter bandwidth, where attenuation is equal above and below the carrier, and so for each sideband.
The carrier, and both sidebands will pass through the filter.
Now look at a filter being used for upper sideband. The carrier frequency set to the bottom edge of the filter passband.
The lower sideband will be blocked by the filter, but the upper sideband will pass through.
As the carrier oscillator has been shifted down, the VCO will need to be shifted UP by the same amount so that the output is still on the correct frequency.
Now this same filter is being used for lower sideband. The carrier frequency set to the top edge of the filter passband.
The lower sideband will now pass through the filter, but the upper sideband will now be blocked.
As the carrier oscillator has been shifted up, the VCO will need to be shifted down by the same amount so that the output is still on the correct frequency.
The filter used for SSB signals only needs to be as wide as the modulating bandwidth. For communications equipment, this is usually no more than 3KHZ.
As the bandwidth of AM and FM signals is much higher, a separate, wider filter needs to be used for these modes.