Single Sideband Frequencies and Band Edges
When a radio-frequency signal is modulated using amplitude-modulation, the single carrier signal is spread into a carrier signal at the original transmission frequency, as well as a set of transmitted frequencies above and below the original transmission frequency. These additional frequencies are called sidebands.
For voice over ham radios, the audio frequencies that modulate the carrier frequency are about 3kHz wide. The additional frequencies, (sidebands), transmitted are about 3 kHz wide on either side of the carrier frequency.
The audio information is carried in the sideband frequencies. The two sidebands are duplicates of each other. For single sideband, (SSB), one of the sidebands is removed before transmission. For upper sideband, (USB), the lower sideband is removed. For lower sideband, (LSB), the upper sideband is removed.
When using a transmitter that displays the carrier frequency, you need to keep in mind that for USB, the maximum frequency transmitted is the carrier frequency + 3kHz, and that for LSB, the minimum frequency transmitted is the carrier frequency - 3kHz.
Now, for the test questions!
When using a transceiver that displays the carrier frequency of phone signals, which of the following displayed frequencies will result in a normal USB emission being within the band?
A. The exact upper band edge
B. 300 Hz below the upper band edge
C. 1 kHz below the upper band edge
D. 3 kHz below the upper band edge
The correct answer is D. The sideband in USB contains frequencies up to 3 kHz above the carrier frequency, so the operator should keep the frequency reading 3 kHz below the frequency band edge.
When using a transceiver that displays the carrier frequency of phone signals, which of the following displayed frequencies will result in a normal LSB emission being within the band?
A. The exact lower band edge
B. 300 Hz above the lower band edge
C. 1 kHz above the lower band edge
D. 3 kHz above the lower band edge
Again, D is the correct answer. Here, the sideband can contain frequencies that are up to 3 kHz below the carrier frequency, so the display should be set to 3 kHz above the lower band edge.
With your transceiver displaying the carrier frequency of phone signals, you hear a DX station's CQ on 14.349 MHz USB. Is it legal to return the call using upper sideband on the same frequency?
A. Yes, because the DX station initiated the contact
B. Yes, because the displayed frequency is within the 20 meter band
C. No, my sidebands will extend beyond the band edge
D. No, USA stations are not permitted to use phone emissions above 14.340 MHz
The correct answer is C. 14.349 MHz plus the 3 kHz for the uppers sideband results in a maximum frequency of 14.352 MHz. The end of the band is at 14.340 MHz. See the extra class band plan.
With your transceiver displaying the carrier frequency of phone signals, you hear a DX station's CQ on 3.601 MHz LSB. Is it legal to return the call using lower sideband on the same frequency?
A. Yes, because the DX station initiated the contact
B. Yes, because the displayed frequency is within the 75 meter phone band segment
C. No, my sidebands will extend beyond the edge of the phone band segment
D. No, USA stations are not permitted to use phone emissions below 3.610 MHz
C is the correct answer. The carrier frequency of 3.601 MHz minus the 3 kHz sideband frequency is 3.598 MHz. Which is below the edge of the portion of the band allowed for phone transmissions.