The Mixer submenu controls the measurement of the mixing products generated by an external mixer that is supplied with two independent RF signals. Together with the Harmonic Distortion measurement and the arbitrary configuration of generator and receiver frequencies (Port Configuration), the mixer mode is included in option R&S ZVA-K4.
Mixer Measurements
RF mixers convert an RF signal at one frequency into a signal at another frequency. The frequency that is to be shifted is applied at the RF input and the frequency shifting signal (from a local oscillator, LO) is applied to the RF mixer's LO port, resulting in an output signal at the mixer's Intermediate Frequency (IF) port.
For a given RF signal, an ideal mixer would produce only two IF outputs: one at the frequency sum of the RF and LO (IF = RF + LO), and another at the frequency difference between the RF and LO (IF = |RF – LO|). Filtering can be used to select one of these IF outputs and reject the unwanted one.
In the mixer mode the analyzer provides the following functionality:
Configuration of the RF and LO signals and measurement of the generated IF signal, see Define Mixer Mode andMixer Signal Diagrams.
Power calibration of the signal sources and of the IF receiver; see Mixer Power Calibration.
The mixer mode can be used also to test important performance parameters of RF mixers such as frequency ranges, conversion loss, compression, and isolation.
Mixer Meas and Freq Conv Off toggle between the (frequency-converting) mixer mode and normal (non frequency converting) operation.
Define Mixer Meas... opens a dialog to configure the mixer input signals.
Mixer Power Cal... opens a dialog to perform a power calibration of the signal sources and of the IF receiver.
The two softkeys Mixer Meas and Freq Conv Off toggle between the (frequency-converting) mixer mode and normal operation, where the analyzer measures the unconverted fundamental wave.
Freq Conv Off also disables an active harmonic distortion measurement. A Mix label in the channel list indicates that the mixer mode is active.
Remote control:
[SENSe<Ch>:]FREQuency:CONVersion MIXer | FUNDamental
Opens a configuration dialog for the mixer input signals.
In the upper part the Define Mixer Measurement dialog shows a diagram with the RF and LO signals, the mixing product (IF), and the current frequency and power ranges for all signals. Below the dialog provides the following control elements:
The port selection list contains all analyzer ports or external generators which can provide the local oscillator (LO) signal. Ports no. 1 and 2 are always used for the RF signal and the measured IF signal (mixing product), so they are not included in the list. Generators must be configured explicitly in the System Configuration – External Generators dialog before they appear in the list. None means that the input signal at LO (if available) is not controlled by the analyzer.
Config Ext. Generators... opens the System Configuration – External Generators dialog for adding and configuring external generators.
Set Power... opens a dialog to control the power of the RF and the LO signals.
Set Frequencies... opens a dialog to control the frequency of the RF and the LO signal and the analyzer (IF signal) frequency.
[SENSe<Ch>:]FREQuency:CONVersion:MIXer:LOINternal <port_no> [SENSe<Ch>:]FREQuency:CONVersion:MIXer:LOEXternal <gen_no>
The mixer signal diagrams show the parameters of the mixer input signals (RF, LO) and of the mixing product (IF signal, output). The diagrams appear in the Mixer Measurement, Set Power, and Set Frequencies dialogs.
The RF signal is the stimulus signal that the analyzer generates with the current channel settings. After a reset the frequency and power of the RF signal is as defined in the Channel – Stimulus menu. The RF signal parameters can be changed in the Set Power... and Set Frequencies... dialogs.
The Local Oscillator (LO) signal is an additional RF signal that is either generated by the network analyzer (at one of the ports that are not used for the RF and IF signals) or by an external generator.
The IF signal is the mixer output signal (mixing product), which is at one of the following frequencies: IF = LO + RF or IF = |LO – RF|, i.e. LO – RF (for LO > RF) or IF = RF – LO (for RF > LO). The IF frequency is selected in the Set Frequencies... dialog.
The signal description above with the swept RF signal and the LO signal at a fixed frequency corresponds to the default configuration. In the Set Frequencies dialog, you can interchange the role of the signals, selecting any of the signals as a Sweep/CW signal, a signal at Fixed frequency or at the calculated sum or difference frequency (Auto).
The labeling of the complete diagram depends on the sweep type.
Frequency sweep
For a frequency sweep, the signal diagram is labeled as follows:
RF signal: Fixed port number (1), CW power, frequency sweep range.
LO signal: Signal source (analyzer port or external generator), fixed power and frequency.
IF signal: Fixed port number (2), frequency range = (sweep range + LO) or |sweep range – LO|.
Power sweep
For a power sweep, the signal diagram is labeled as follows:
RF signal: Fixed port number (1), power sweep range (or fixed power, if the LO signal is swept), CW frequency.
LO signal: Signal source (analyzer port or external generator), fixed power (or power sweep range, if the RF signal is at a fixed power), CW frequency.
IF signal: Fixed port number (2), fixed frequency = (RF + LO) or |RF – LO|.
Time or CW mode sweep
For a Time or CW Mode sweep, the signal diagram is labeled as follows:
RF signal: Fixed port number (1), fixed power, CW frequency.
LO signal: Signal source (analyzer port or external generator), fixed power, CW frequency.
The Set Power dialog defines the power of the RF and the LO signals.
The diagram contains the mixer signal diagram and the following control elements:
The RF Power radio button groups specify how the power for each signal is defined. The roles of the mixer input signals RF and LO are interchangeable: One signal is at the analyzer's channel power (Sweep or CW, the signal is swept if a power sweep is active; it is at fixed power (CW) for the other sweep types), the other is at the Fixed power defined below.
The input fields in the Sweep/CW Power panel define the channel power and overwrite the power settings in the Channel – Stimulus and Channel – Power Bandwidth Average menus. The sweep range or CW power is assigned to the signal with Sweep/CW power definition.
Fixed Power defines the power to be assigned to the signal with Fixed power definition.
SOURce<Ch>:]FREQuency:CONVersion:MIXer:FUNDamental RF | LO SOURce<Ch>:]FREQuency:CONVersion:MIXer:PFIXed <power>
Controls the frequency of the RF and the LO signal and the analyzer (IF signal) frequency.
The ...Frequency radio button groups specify how the frequency for each signal is defined. The roles of the three signals RF, IF, LO are interchangeable: One signal is at the analyzer's channel frequency (Swept/CW, the signal is swept if a frequency sweep type is active; it is a CW signal for the other sweep types), the second is at the Fixed frequency defined below, the frequency of the third signal is calculated according to the selected Conversion formula.
The input fields in the Swept Frequency panel define the channel frequency and overwrite the Channel – Stimulus settings. The sweep range or CW frequency is assigned to the signal with Swept/CW frequency definition.
Fixed Frequency defines the frequency to be assigned to the signal with Fixed frequency definition.
Conversion selects the frequency of the signal with Auto frequency definition, see background information below.
Conversion formulas
The IF signal can be at the sum or at the difference of the RF and LO frequencies.
IF = RF – LO means that the RF signal is down-converted (upper sideband). The analyzer automatically switches to IF = LO – RF if the LO frequency is above the RF input frequency.
IF = LO – RF means that the LO signal is down-converted (lower sideband). The analyzer automatically switches to IF = RF – LO if the RF input frequency is above the LO frequency.
IF = LO + RF means that the RF input signal is up-converted.
In a frequency sweep mode where one of the input frequencies varies over a definite range, the IF signal also covers a frequency range of the same width. An error message is displayed if the IF frequency exceeds the maximum frequency range of the analyzer.
If the RF or LO signal is in Auto mode, the formulas for IF are automatically converted, and the analyzer calculates the RF or LO frequency from the other frequencies.
[SENSe<Ch>:]FREQuency:CONVersion MIXer:FFIXed <frequency> [SENSe<Ch>:]FREQuency:CONVersion MIXer:FIXed RF | IF | LO [SENSe<Ch>:]FREQuency:CONVersion MIXer:FUNDamental RF | IF | LO [SENSe<Ch>:]FREQuency:CONVersion MIXer:TFRequency DCLower | DCUPper | UCONversion [SENSe<Ch>:]FREQuency:STARt etc.
Opens a dialog to perform a power calibration of the signal sources and of the IF receiver. A power calibration ensures accurate levels of the mixer input signals (RF and LO source power calibration) and an accurate power measurement of the mixer output signal (IF receiver calibration). The necessary calibration steps are automatically performed across the entire frequency range of the active mixer measurement (Set Frequencies).
Mixer Power Cal procedure and example
Due to the different frequency ranges of the input and output signals and the external equipment needed, the mixer power calibration must be performed in several steps. For a test setup where the RF and LO signals are provided by port 1 and an external generator, respectively, where the RF signal is swept, and where the IF signal is analyzed at port 2, the following test setups are required:
Source power calibration for the RF signal. A power sensor is connected to port 1. The RF power (red) is calibrated over the selected RF sweep range. As a preparative for step 2 the analyzer also calibrates the source at the fixed IF frequency. The correction data for both calibration sweeps is stored.
Receiver power calibration for the IF signal. No external device is needed. The receiver (port 2) is calibrated at the IF frequency using the source signal from port 1 (red) calibrated in the first step.
Source power calibration for the LO signal, provided by an external generator. A power sensor is connected to the generator's RF output (red signal). The analyzer controls the generator, its RF power (red) is calibrated at the selected IF frequency. No RF connection to or from the network analyzer is needed.
Config Ext. Power Meters... opens the System Configuration – External Power Meters dialog for adding and configuring external power meters.
Take Cal Sweep in the three numbered panels start the calibration sweeps for the RF source, IF receiver, and the LO source, respectively. The calibration sweep are performed at the test settings defined in the Source Power Cal and Receiver Power Cal menus. A popup box shows the progress of the calibration.