Frequency Offset Mode (FOM) provides the capability to have the VNA Sources tune to frequencies that are different (offset) from the VNA Receivers.
VNA Option 080 or S9x080A provides you with the hardware and basic software capability to make Frequency Offset Measurements. This topic discusses the VNA settings that are relevant to making these types of measurements. See Frequency Converting Device Measurements for more information on making specific device measurements.
How to make Frequency Offset settings |
Using Hardkey/SoftTab/Softkey |
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Note: Source2 supplies power for ports 3 and 4. Turn Source2 power ON using the Power and Attenuators dialog. This (Frequency Offset) is the only dialog for controlling the frequency of Source 2. Learn more about Source2. Note: Source3 is an RF signal to the rear-panel connector. Turn Source3 power ON using the Power and Attenuators dialog. This (Frequency Offset) is the only dialog for controlling the frequency of Source 3. Learn more about Source3. Frequency Offset (ON/OFF) Enables Frequency Offset Mode on ALL measurements that are present in the active channel. When FOM is NOT enabled, all frequencies are the same as the active channel. Tip: First make other settings on this dialog box, then click Frequency Offset ON. Primary The current Active Channel settings. When a Source or Receiver is coupled to the Primary settings, its Sweep Type is the same as that of the Primary. The frequency settings of the coupled range are mathematically derived from the Primary settings using the Multiplier, Divisor, and Offset values. With this approach, only the Primary settings need to be changed in order to affect change in the coupled Sources and Receivers. Changes to the Primary channel settings occur when Frequency Offset is checked ON. See example using Primary and Coupled setting. Tip: Primary settings are ONLY used when Sources and Receivers are Coupled. It is often easier to Uncouple, then set Sources and Receivers independently. Source and Source2 if available. Learn more about Internal Second Source. Receivers All receivers that are used in the channel, including Reference receivers, are tuned to the specified frequency settings. Mode Coupled Source and Receiver settings are mathematically derived from the Primary settings using Multiplier, Divisor, and Offset values. Learn more. Uncoupled Source and Receiver settings are entered independently, without reference to Primary settings. When Uncoupled, Source and Receiver Ranges can use separate sweep types. Sweep Type Click to change the type of sweep for each range. Only available for Primary and Uncoupled Sources and Receivers. Settings To change settings, click IN the appropriate Settings cell, then click Edit.
X-Axis Annotation Select the settings to be displayed on the X-Axis: X-Axis Point Spacing Only available when a Segment Sweep Type is selected as the X-Axis display. Learn more.
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Coupled Formulas: Range Start = [Primary Start x (Multiplier / Divisor)] + Offset Range Stop = [Primary Stop x (Multiplier / Divisor)] + Offset Where: Offset Specifies an absolute offset frequency in Hz. For mixer measurements, this would be the LO frequency. Range is +/- 1000 GHz. Offsets can be positive or negative. Multiplier Specifies (along with the divisor) the value to multiply by the stimulus. Range is +/- 1000.
Divisor Specifies (along with the multiplier) the value to multiply the stimulus. Range is 1 to 1000. |
This dialog will vary depending on the sweep type: Linear and Log frequencyUncoupled Log sweep yields invalid data whenever the sources are offset from the receivers. Select Start/Stop or Center/Span Frequency Enter values Points (Primary only) Enter number of data points for the sweep. PowerCW Freq Enter frequency in Hz. Points (Primary only) Enter number of data points for the power sweep. CW TimeCW Freq Enter frequency in Hz. Sweep Time Enter time to complete one sweep. Enter 0 for the fastest sweep. Segment Sweep Edits are made exactly like the standard segment table.For Advanced Users: Uncoupled Segment Sweep offers great flexibility in configuring measurements. In segment sweep mode:
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Although the Frequency Offset settings can be used with many types of devices, these examples include mixer terminology.
See a Mixer Compression and Phase (AM-PM) Measurement using FOM.
See a calibrated FOM conversion loss example.
1. |
Fixed LO - Upconverter
Make the following settings on the FOM dialog Source: Uncoupled Sweep Type: Linear Click Settings, then Edit. In the Source dialog: Start Frequency = 1000 MHz Stop Frequency = 1200 MHz Receiver: Uncoupled Sweep Type: Linear Click Settings, then Edit. In the Receiver dialog: Start Frequency = 2500 MHz Stop Frequency = 2700 MHz LO Settings Set external source to CW - 1500 MHz. Source2: Uncoupled (Only with Second VNA Internal Source) Sweep Type: CW Time Click Settings, then Edit. In the Source2 dialog: CW Frequency = 1500 MHz |
2. |
Fixed LO - Downconverter (Input < LO)
Make the following settings on the FOM dialog Primary: Not used Source (Input): Uncoupled Sweep Type: Linear Click Settings, then Edit. In the Source dialog: Start Frequency = 1000 MHz Stop Frequency = 1100 MHz Receiver (Output): Coupled Sweep Type: Linear Click Settings, then Edit. In the Receiver dialog: Offset: 2500 MHz Multiplier: -1 (Minus one) LO Settings
Sweep Type: CW Time Click Settings, then Edit. In the Source2 dialog: CW Frequency = 2500 MHz |
3. |
Swept LO - Fixed Output - UpconverterSwept External LO measurements in Frequency Offset Mode can be very difficult. The external LO source must be synchronized with the swept output or input (as in this case). See Synchronizing and External Source Control to see how this is done. The Frequency Converter Application Opt S9x083A/B performs makes these measurements easily.
Make the following settings on the FOM dialog Source: Uncoupled Sweep Type: Linear Click Settings, then Edit. In the Source dialog: Start Frequency = 1000 MHz Stop Frequency = 1100 MHz Receiver: Uncoupled Sweep Type: CW Time Click Settings, then Edit. In the Receiver dialog: CW Frequency = 2500 MHz LO Settings
Sweep Type: Linear Click Settings, then Edit. In the Source2 dialog: Start Frequency = 1500 MHz Stop Frequency = 1400 MHz |
4. |
Power Sweep for MixersTo measure the gain compression of a mixer, the input power to the mixer is swept. The input and output frequencies are fixed but offset from one another. This is a good use of Coupled settings because the same compression test can be performed at several different frequencies. With coupled Source and Receiver ranges, the Primary (channel) frequency can be easily changed from the front panel. The coupled source and receiver frequencies will update accordingly.
Make the following settings on the FOM dialog Primary: Sweep Type: Power Sweep Click Settings, then Edit. In the Primary dialog: CW Frequency = 1500 MHz Source: Coupled Default settings make CW Frequency: 1500 MHz (same as Primary) Receiver: Coupled Default settings make Sweep Type: CW Time Click Settings, then Edit. In the Receiver dialog: Offset = 500 MHz LO Settings
Sweep Type: Power Sweep Click Settings, then Edit. In the Source2 dialog: CW Frequency = 500 MHz |
Test Set Reference Switch
PNA-X and N522x models have a switch in the test set that allows you to bypass the port 1 reference receiver through the front panel Reference 1 connectors. This switch lets you easily switch between standard S-Parameter measurements and measurements using a reference mixer. You could use this feature to make standard S11 measurements and converter transmission measurements relative to a reference ("golden") mixer.
Note: The Frequency Converter Application Option S93083A/B simplifies the task of making extremely accurate phase measurements on MOST frequency converting devices.
How to access the RF Path Config dialog box |
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Using Hardkey/SoftTab/Softkey |
Using a mouse |
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Note: This feature is available on PNA-X and N522x models. R1 Input Path Internal Connects the port 1 source directly to the R1 receiver. External Allows direct access to the R1 receiver through the Reference 1 front-panel connectors. See specifications which include a block diagram of reference switch. |