5-28 Keysight N5227B Service Guide
Theory of Operation
Synthesized Source Group Operation
5-
Understanding LFE vs. Legacy PNA Environment
To understand several parts of the LFE board behavior, we must consider the
non-LFE behavior of the PNA (i.e., what is already in place on different boards
that did not change).
On the synthesizer board, there is a LFE output coming almost directly from
the direct digital synthesis (DDS). There is a 250 MHz Low Pass Filter. The
low frequency extension uses this output to100 MHz.
A C-R High Pass Filter limits the lowest frequency.
With LFE mode, we use dedicated mixers, which are the LFE board. These
mixers downconvert the RF signals in LFE mode and create dedicated IF
signals. These IF signals are then sent to the IF Mux board.
On the IF MUX board, the configuration between the Main IF signals and LFE
IF signals are very different.
2
1.0000 to
1.95313
Thru
4
DDS_CLK
LFE
1.95313 to
3.90000
4
DDS_CLK
LFE
3.90000 to
7.81000
4
DDS_CLK
LFE
7.81000 to
9.9000
4
DDS_CLK
LFE
3
9.9000 to
10.01000
IF2
4
DDS_CLK
LFE
4
10.01000 to
19.99000
Thru
4
DDS_CLK
LFE
5
1.99000 to
31.25000
IF1
4
DDS_CLK
LFE
31.5000 to
53.0000
4
DDS_CLK
LFE
6
53.0000 to
62.50000
IF2
4
DDS_CLK
LFE
62.50000 to
1000.0000
4
DDS_CLK
LFE
Band
A11
LO
Synthesizer
(VCO)
IF Mode
DIV / N
Synth RF
Path
Synth RF
Output
