What kind of input signal could be used to test the amplitude linearity of a single-sideband phone transmitter while viewing the output on an oscilloscope?

A two-tone audio-frequency sine wave.

Two-tone tests can help determine whether the radio is able to pick up on each frequency. For full discussion of two-tone testing, please see Wikipedia's article on Two-tone testing

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From kj6prf:

When testing for linearity in a radio system, we're making sure that our two signals are being added kind of like the first example, except with sines and cosines instead of a simple scalar value.

If our system is nonlinear, this will cause distortion and the resulting output will sound strange or behave unpredictably.

When you test for linearity, you are testing how two inputs are being added together and checking that the output is what you would expect it to be.

If a system is linear, it shouldn't matter if two inputs are scaled or added together before you input them into the system or after, the resulting output should be the same regardless. In nonlinear systems, things don't necessarily add together as you might expect.

EXAMPLE 1: As an example, the function y = 2x is linear. It doesn't matter if we take two inputs, say x=3 and x=4, and add first add them together and then perform the operation, or perform the operation twice and then add them together.

Symbolically, y = 2∗(3+4) = 2∗(7) = 14 as opposed to y = 2∗(3) + 2∗(4) = 6+8 = 14.

The order doesn't matter because this is a linear system.

EXAMPLE 2: Take as a counterexample, y = x². In this case it matters whether the inputs are added before or after the operation because y = (3+4)² = 49 but y = 3²+4² = 25. This is a nonlinear relationship.

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What does a two-tone test illustrate on an oscilloscope?

Linearity of a SSB transmitter.

Two-tone tests can help determine whether the radio is able to pick up on each frequency. For full discussion of two-tone testing, please see Wikipedia's article on Two-tone testing

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From kj6prf:

When testing for linearity in a radio system, we're making sure that our two signals are being added kind of like the first example, except with sines and cosines instead of a simple scalar value.

If our system is nonlinear, this will cause distortion and the resulting output will sound strange or behave unpredictably.

When you test for linearity, you are testing how two inputs are being added together and checking that the output is what you would expect it to be.

If a system is linear, it shouldn't matter if two inputs are scaled or added together before you input them into the system or after, the resulting output should be the same regardless. In nonlinear systems, things don't necessarily add together as you might expect.

EXAMPLE 1: As an example, the function y = 2x is linear. It doesn't matter if we take two inputs, say x=3 and x=4, and add first add them together and then perform the operation, or perform the operation twice and then add them together. Symbolically, y = 2*(3+4) = 2*(7) = 14 as opposed to y = 2*(3) + 2*(4) = 6+8 = 14. The order doesn't matter because this is a linear system.

EXAMPLE 2: Take as a counterexample, y = x^2. In this case it matters whether the inputs are added before or after the operation because y = (3+4)^2 = 49 but y = 3^2+4^2 = 25. This is a nonlinear relationship.

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How can a double-sideband phone signal be produced?

By modulating the supply voltage to a class C amplifier.

For more information, please see Wikipedia's article on Power amplifier classes

Also, see Electronics Tutorials site for article on Amplifier Classes

And, see Ham Radio Stack Exchange site for the article on Why does a Class-C non-linear power amp distort SSB but does not distort AM?

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What type of signals are used to conduct an SSB two-tone test?

Two non-harmonically related audio signals that are within the modulation bandpass of the transmitter.

Two-tone tests can help determine whether the radio is able to pick up on each frequency. For full discussion of two-tone testing, please see Wikipedia's article on Two-tone testing

---

From kj6prf:

When testing for linearity in a radio system, we're making sure that our two signals are being added kind of like the first example, except with sines and cosines instead of a simple scalar value.

If our system is nonlinear, this will cause distortion and the resulting output will sound strange or behave unpredictably.

When you test for linearity, you are testing how two inputs are being added together and checking that the output is what you would expect it to be.

If a system is linear, it shouldn't matter if two inputs are scaled or added together before you input them into the system or after, the resulting output should be the same regardless. In nonlinear systems, things don't necessarily add together as you might expect.

EXAMPLE 1: As an example, the function y = 2x is linear. It doesn't matter if we take two inputs, say x=3 and x=4, and add first add them together and then perform the operation, or perform the operation twice and then add them together.

Symbolically, y = 2x(3+4) = 2x(7) = 14 as opposed to

y = 2x(3) + 2x(4) = 6+8 = 14. The order doesn't matter because this is a linear system.

EXAMPLE 2: Take as a counterexample, y = x². In this case it matters whether the inputs are added before or after the operation because

y = (3+4)² = 49 but y = 3²+4² = 25.

This is a nonlinear relationship.

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Tags: none