Technical Notes; Measuring Principle - Deepace KC901V Manual

Chapter Six Technical Specification
6.1 Measurement Theory
KC901V's circuit has a signal source and two receivers.
Signal source is divided into two frequency bands: The signal which is lower than
60MHz (except audio frequency source) is produced by DDS directly; the one which is
higher than 60MHz is produced by PLL. The signal sources of two frequency bands are
gated by a RF switch and they combined into one RF signal to output.
Both two receivers are the digital-IF synchronous receivers. The reason why S21
function is "simplified vector" is that instrument's receivers only detect the forward
signal while using this function and it can't detect the reverse signal. So it can only
run the simplified calibration model and it can also only remove the errors of the fre-
quency response.
Check Chart 6-1 for KC901V's schematic diagram.
When testing S11, the CW which is produced by signal source will enter the for-
ward signal through forward shunt before entering into the bridge. Then it will take
out the reverse signal from the directional bridge. Finally, it will input from port 1. The
forward signal and reverse signal will enter the two separate receivers and enter ADC
after the double conversion. Finally, it converts into digital signal and enter FPGA to
be processed. KC901V takes the inner product of vectors to do digital phase discrimi-
nation as well as takes root-mean-square detector to measure the range. About the
data of RF measurement, they all come out by calculating the forward/reserve signal
and the phase difference.
When testing S21, signal source will change its direction and output from port 2.
Before going through the DUT, do the forward test first. After going through DUT, sig-
nal will enter from port 1 and then do the transmission detection. The result of
Chart 6-1: KC901V's Schematic Diagram
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