The invention relates to a frequency change
system group
delay test method which comprises the following steps of: generating an FM (
Frequency Modulation)
carrier signal of which the carrier frequency is the
center frequency of a working
frequency band of a frequency change
system by a
signal source; then dividing the
signal into two paths, wherein one path of
signal is input to the frequency change
system by an attenuator and used as the input of a first A / D (Analog-to-Digital) converter by the attenuator after being output by the frequency change system, the other path of signal is used as the input of a second A / D converter, and the two A / D
converters synchronously sample data by using the same reference
clock; then respectively carrying out Hilbert transformation,
digital down conversion and non-coherent
demodulation on two paths of A / D sampled data; and carrying out digital phase comparison on the two paths of demodulated base band signals to obtain a group
delay value of the frequency change system. A group
delay test result of all frequency points of the frequency change system in the
frequency band can be obtained by changing the carrier frequency of the FM
carrier signal in the working bandwidth of the frequency change system and repeating the
processing; and the measuring precision depends on system heat
noise, the correcting precision of a test cable and A / D sampling resolution.