# Homework Help: Bandwidth in (kHz)

1. Jul 9, 2012

### qduy

Please help me to find out, what is the bandwidth in (kHz) of an AM (SSB-SC) signal with a carrier frequency of 941 kHz and a baseband signal that has frequency components from 20 Hz to 19 kHz? thanks

2. Jul 10, 2012

### Staff: Mentor

Hi qduy. Explain what you understand by an AM (SSB-SC) signal.

3. Jul 14, 2012

### qduy

Single-sideband suppressed-carrier (SSB-SC) is a refinement of amplitude modulation that more efficiently uses electrical power and bandwidth.

4. Jul 15, 2012

### Staff: Mentor

Perfect!

Now, can you sketch the spectrum of an AM signal having the same carrier and baseband that was specified for this exercise.

I see you are very new to Physics Forums, so welcome!

Maybe you haven't yet learnt how to include graphics here, so for your answer I'll also accept a good verbal description of the sketch in question, but please make your answer both clear and concise; we all know a picture is actually worth a thousand words.

Last edited: Jul 15, 2012
5. Jul 15, 2012

### CWatters

Perhaps start with the diagram for regular AM showing the sidebands and the carrier. Then rub bits off :-)

6. Oct 10, 2012

### Bbqonion

I did an experiment in school to find the bandwidth of an amplifier with negative feedback.
I cound not get a high enough input voltage with the signal generator. Is a terminal of the signal generator supposed to be connected to the earth?

7. Oct 10, 2012

### Staff: Mentor

Hi Bbqonion, welcome to Physics Forums.

It is best that you start a new thread for your question, as it is not a continuation of the thread you have piggy-backed onto.
By "the earth" do you mean that big asteroid sort of thing inhabited by simians? Then the answer is no. Not directly.

At the output of your signal generator are two terminals, one being the signal itself and the other being the generator circuit's earthâ€”its zero volt level. Both terminals need to be connected to the amplifier under test, with the signal generator earth connecting to your amplifier circuit earth, so that all voltages are referenced to a common zero volt level.

Usually the output terminals of the signal are combined into one as a coaxial socket, so connection of both takes places simultaneously, and the user doesn't have to remember to make two connections.

If you overlook that common earth connection, then a tiny level of signal may still get through due to some capacitive coupling, but expect to have it swamped by local noise and powerline hum (50Hz/60Hz).