Amateur ExtraE4B10
Which of the following methods measures intermodulation distortion in an SSB transmitter?
B
Answer
Receivers, transmitters, and measurements
Type
A
Modulate the transmitter using two RF signals having non-harmonically related frequencies and observe the RF output with a spectrum analyzer
B
Modulate the transmitter using two AF signals having non-harmonically related frequencies and observe the RF output with a spectrum analyzer
C
Modulate the transmitter using two AF signals having harmonically related frequencies and observe the RF output with a peak reading wattmeter
D
Modulate the transmitter using two RF signals having harmonically related frequencies and observe the RF output with a logic analyzer
Answer Notes
To measure intermodulation distortion (IMD) in a Single Sideband (SSB) transmitter, you perform a standard 'two-tone test.' This involves injecting two audio frequency (AF) signals into the microphone input. These tones must not be harmonically related (for example, 700 Hz and 1900 Hz).
The transmitter's RF output is then observed on a spectrum analyzer. If the transmitter's amplifier stages are not perfectly linear, unwanted mixing products (IMD) will appear as extra, distinct peaks on the analyzer display adjacent to the two desired RF tones.
Using harmonically related tones is a poor test because IMD products could fall exactly on harmonic frequencies, masking the distortion. Furthermore, you must inject AF signals rather than RF signals to test the entire modulation and amplification chain of the SSB transmitter.
Previous · E4B09
Which of the following can be measured by a two-port vector network analyzer?
Next · E4B11
Which of the following can be measured with a vector network analyzer?