Configuring the Signal in the RF Domain
R&S
®
SMW200A
450User Manual 1175.6632.02 ─ 16
Keep the order when performing LO Level adjustments for subsequent instru-
ments
When you perform LO level adjustments in several interconnected signal generators,
always start with the first Rohde & Schwarz signal generator, and continue in the order
of the following Rohde & Schwarz signal generators. This sequence is necessary,
because the second instrument adjusts its internal gain as long as the levels are accu-
rate and then keeps this adjustment untouched. If you now would change the prede-
cessor, the level of the second would change accordingly and its adjustment would no
longer be correct.
7.5.1 Required Options
The equipment layout for using the LO Coupling function is included in:
●
Option Phase Coherence (R&S SMW-B90)
7.5.2 Phase Coherence
Phase coherence of RF signals designates a defined, constant delta phase between
two or more RF carrier signals with the same frequency or a multiple of the frequency.
If two signal generators are coupled via their 10 MHz reference, they are generating
the same frequency but only from the long term perspective. Having a closer look into
the instantaneous differential phase (“delta phase”) of these two RF signals, this is
instable due to:
●
Phase noise of the two synthesizers
●
Weak coupling at 10 MHz and a long synthesis chain up to the RF domain
●
Temperature differences which cause a change of the effective electrical length of
some synthesizer components
Most critical for a stable delta phase is the thermal RF phase fluctuation between multi-
ple RF synthesizers. These fluctuations can be minimized by using a common synthe-
sizer, that means a common local oscillator (LO) signal for all RF carrier. Only if this
LO signal (which is internally used for upconverting the baseband signal to the RF) is
Local Oscillator Coupling
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