Rohde & Schwarz 1145.1010.04/05/06, Operating Manual

Page: 354 / 813

Channel Menu R&S
®
ZVA/ZVB/ZVT
1145.1084.12 4.192 E-6
receiver mixer of the analyzer port 1, where a small fraction of the mixer product RF + 2*IF can be
reflected back towards the DUT. If this spurious wave a'
1
passes the DUT, then it is received as b'
2
at
port 2, together with the wanted signal b
2
.
LO > RF implies that LO = RF + IF. The mixer at port 2 converts both the wanted signal b
2
and the
spurious signal b'
2
which is at the frequency RF' = IF + LO, to the same IF frequency. The response of
an ideal, infinitely steep bandpass filter with a pass band between B
-
and B
+
looks as follows:
For a wide bandpass, the spurious response flattens the filter edges.
The spurious signal can be eliminated by dividing the sweep range into two segments with
different LO settings:
•
In the low-frequency segment, ranging up to the center frequency of the bandpass filter, the
frequency of the local oscillator is set to LO < RF. This ensures that the spurious signal b'
2
is
not measured at port 2.
•
In the high-frequency segment, starting at the center frequency of the bandpass filter, the
frequency of the local oscillator is set to LO > RF. If the center frequency is larger than B
+
–
2*IF, then there is no distortion from b'
2
.
Remote control:
[SENSe<Ch>:]FREQuency:SBANd POSitive | NEGative | AUTO
ALC (All Chans)
Enable or disables the Automatic Level Control (ALC) for all channels. ALC keeps the level of the a
waves at a constant value, irrespective of the DUT's input impedance. The measurement speed is
slightly reduced.
Remote control: DIAGnostic:ALC:SETTings[:STATe] ON | OFF
Low Phase Noise
Reduces the phase noise of the source signals. The measurement speed is slightly reduced.
Remote control: [SENSe<Ch>:]FREQuency<1>:LPNoise ON | OFF