Chapter 3 CAT (Cable and Antenna Test) Mode

 

CAT Mode is typically used to test an entire transmission system, from the transmitter to the antenna. This process is sometimes referred to as Line Sweeping.

 

CAT Mode is similar to NA (Network Analyzer) Mode. Learn more in the Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.

 

CAT Mode Distance to Fault measurements are discussed in Chapter 4 DTF (Distance to Fault) Measurements, in the B-Series N9938-90006 (Unabridged) User's Guide.

 


 

IMPORTANT! For CAT and NA modes, limit lines do not apply where F1 = F2.

 

In this Chapter

“Measurement Selection”

“Quick Settings Table”

“Frequency Range”

“Scale Settings”

“Averaging”

“Smoothing”

“Single or Continuous Measure”

“Resolution (Number of Data Points)”

“Sweep Time”

“Output Power”

“Interference Rejection”

“Coupled Frequency”

“Return Loss Measurements”

“1-Port Cable Loss Measurements”

“2-Port Insertion Loss Measurements”

 

See also

Chapter 6, “Calibration for NA, CAT, and VVM Modes”

“All about Markers”

“All about Limit Lines”

“All about Trace Math”

Making 75Ω (ohm) Measurements at the FieldFox Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.

Cat Mode Settings

Select CAT Mode before making any setting in this chapter.

How to select CAT Mode

  1. Press Mode.
  2. Then CAT/TDR.

Measurement Selection

How to select a CAT Mode Measurement

Learn more about the following measurements in the Supplemental Online Help: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.).

 

Press Measure 1.

 

Then choose one of the following: These softkeys also appear after CAT Mode is selected.

 

Quick Settings Table

Both CAT and NA Modes allow you to view and change most relevant settings from a single location. All of these settings are discussed in this chapter and, unless otherwise noted, ALL of these settings can also be made using the standard softkey menus.

 

How to view and change Quick Settings

 

Otherwise, use the numeric keypad,  arrows, or rotary knob to change the value.

Frequency Range

Set the range of frequencies over which you would like to make CAT Mode measurements.

 

When the frequency range is changed after a calibration is performed, the cal becomes interpolated. Learn more in “Interpolation *”.

How to set Frequency Range

Scale Settings

Adjust the Y-axis scale to see the relevant portions of the data trace. The Y-axis is divided into 10 graticules.

 

This setting can be changed at any time without affecting calibration accuracy.

How to set Scale

 

Scale annotation on the FieldFox screen

Reference Line = red arrow

Ref Level = -40 dB

Ref Position = 1

Scale = 2 dB per division

Averaging

Trace Averaging helps to smooth a trace to reduce the effects of random noise on a measurement. The FieldFox computes each data point based on the average of the same data point over several consecutive sweeps.

 

Average Count determines the number of sweeps to average; the higher the average count, the greater the amount of noise reduction.

 

An average counter is shown in the left edge of the screen as Avg N. This shows the number of previous sweeps that have been averaged together to form the current trace. When the counter reaches the specified count, then a ‘running average’ of the last N sweeps is displayed. Average Count = 1 means there is NO averaging.

 

This setting can be changed at any time without affecting calibration accuracy.

 


 

Averaging is often used to increase the dynamic range of a measurement. To achieve the highest dynamic range, select NA mode and reduce the IF Bandwidth setting. Learn more about dynamic range in “Increase Dynamic Range”.

How to set Trace Averaging

  1. Press BW   2.
  2. Then Average N where N is the current count setting.
  3. Enter a value using the numeric keypad. Enter 1 for NO averaging.
  4. Press Enter.
  5. While Trace Averaging is in process, press Sweep 3 then Restart to restart the averaging at 1.

Smoothing

Trace smoothing averages a number of adjacent data points to smooth the peak-to-peak noise values on a displayed trace. The number of adjacent data points that are averaged is known as the smoothing aperture. Aperture is set by specifying a percentage of the X-axis span.

 

Trace smoothing does NOT significantly increase measurement time.

 

Smoothing can be used with any CAT format.

 

When enabled, Smo appears on the FieldFox screen.

 

How to set Smoothing

  1. Press BW   2.
  2. Then Smoothing ON OFF.
  3. Then Sm. Aperture and enter a value between 0 and 25 (percent) using the numeric keypad.
  4. Press Enter.

Single or Continuous Measure

This setting determines whether the FieldFox sweeps continuously or only once each time the Single button is pressed. Use Single to conserve battery power or to allow you to save or analyze a specific measurement trace.

 

This setting can be changed at any time without affecting calibration accuracy.

How to set Single or Continuous

  1. Press Sweep 3.
  2. Then choose one of the following:

 

You can also use Run / Hold +/- to toggle between Single and Continuous.

Resolution (Number of Data Points)

Data points are individual measurements that are made and plotted across the X-axis to form a trace. Select more data points to increase measurement resolution. However, more data points require more time to complete an entire measurement sweep.

 

When the Resolution is changed after a calibration is performed, the calibration becomes interpolated. Learn more in “Interpolation *”.

How to set Resolution

  1. Press Sweep 3 > Resolution
  2. Then choose one of the following:

101 | 201 | 401 | 601 | 801 | 1001 |1601 | 4001 | 10001.

 

Using SCPI, Resolution can be set to any number of points between 3 and 10001. See the Programming Guide at https://www.keysight.com/us/en/lib/resources/service-manuals/keysight-fieldfox-library-help-and-manuals-2153870.html.

Sweep Time

The fastest possible sweep time is always used as the default setting. Use the Min Swp Time setting to slow the sweep time when measuring long lengths of cable.

 

Learn more in the FieldFox Supplemental Help at: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.).

 

The actual sweep time is shown on the FieldFox screen. See “Take the FieldFox Tour”. To increase the sweep time, enter a value that is higher than the actual sweep time. The increase will not be exactly the amount that you enter, as the actual sweep time is the composite of many factors.

 


 

Measurement speed specifications do NOT apply in Temperature Control Mode. Learn more in Chapter 1, “Overview”.

How to set Sweep Time

Output Power

Set the power level out of the FieldFox to High, Low, or manually set power level to a value between High and Low.

 

Generally, the high power setting is used when measuring passive, high-loss devices to place the signal farther from the noise floor. However, for devices that are sensitive to high power levels such as amplifiers, use the Low power setting.

 

For best measurement accuracy, use the Manual power setting at -15 dBm. After calibration, the power level can be decreased for amplifiers, or increased for higher dynamic range.

 

Power Level settings in this mode will NOT change Power Level settings in other modes. To help prevent damage to your DUT, use caution when changing modes with your DUT connected to the FieldFox test ports.

How to set Output Power

  1. Press Meas Setup 4 > Power.
  2. Then Output Power

 

Interference Rejection

Use this setting when you suspect that other signals in the area are interfering with a measurement. Interference may look like a spike or lack of stability in the measurement trace. While monitoring a measurement at a specific frequency, toggle this setting between ON and OFF. If the measurement result decreases while ON, then there is an interfering signal in the area. Continue to make measurements with Interference Rejection ON. However, this will slow the measurement speed.

 

Once enabled, up to SIX sweeps may be required before the interfering signal is neutralized.

 

This setting can be changed at any time without affecting calibration accuracy.

How to set Interference Rejection

  1. Press Meas Setup 4 > Interference Rejection [current setting].
  2. Then choose from the following:

Coupled Frequency

This setting, especially useful for a Return Loss & DTF measurement, allows both measurements to have different frequency ranges.

 

How to set Coupled Frequency

With a Return Loss & DTF measurement present:

  1. Press Meas Setup 4.
  2. Select the DTF measurement (Tr2) using the  arrows ().
  3. Then choose from the following:

Return Loss Measurements

Return loss can be thought of as the absolute value of the reflected power compared to the incident power.

 

When measuring an OPEN or SHORT, all incident power is reflected and approximately 0 dB return loss is displayed.

 

When measuring a LOAD, very little power is reflected and values of 40 dB to 60 dB are displayed.

 

The minus sign is usually ignored when conveying return loss. For example, a component is said to have 18 dB return loss, rather than –18 dB.

How to Measure Return Loss

1-Port Cable Loss Measurements

While all cables have inherent loss, weather and time will deteriorate cables and cause even more energy to be absorbed by the cable. This makes less power available to be transmitted.

 

A deteriorated cable is not usually apparent in a Distance to Fault measurement, where more obvious and dramatic problems are identified. A Cable Loss measurement is necessary to measure the accumulated losses throughout the length of the cable.

 

A 2-port Insertion Loss measurement is usually more accurate than a 1-port Cable Loss measurement. However, to perform a 2-port Insertion Loss measurement, both ends of the cable must be connected to the FieldFox.

 


 

In high-loss conditions, a Cable Loss measurement becomes ‘noisy’ as the test signal becomes indistinguishable in the FieldFox noise floor. This can occur when measuring a very long cable and using relatively high measurement frequencies. To help with this condition, High Power and Averaging use .

How to make a 1-port Cable Loss Measurement

  1. Press Preset then Preset.
  2. Then More then Cable Loss (1-Port)
  3. Connect the cable to be tested.
  4. Press Freq/Dist and enter Start and Stop frequency values of the measurement.
  5. Press Sweep 3 then Min Swp Time. Increase the Sweep Time until a stable trace is visible on the screen. The amount of time that is required increases with longer cable lengths. Learn more in the Supplemental Online Help at: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.
  6. Remove the cable to be tested.
  7. Press Cal 5, then Mechanical Cal.

 

  1. Follow the prompts to perform calibration at the end of the jumper cable or adapter. Learn more about Calibration in “How to Perform a Calibration”.
  2. Connect the cable to be tested.

 


 

Low-level standing waves (also known as ‘ripple’) which may be visible in reflection measurements, can hide the actual loss of the cable. Steps 10 through 13 can minimize the ripple. Perform the measurement with and without steps 10 through 13 and choose the method with the least amount of ripple.

 

  1. Connect a LOAD at the end of the cable to be tested. This limits the reflections to faults that are located in the cable under test.
  1. Press Trace 6 then Math and Memory then Data->Mem to store the trace into Memory.
  2. Remove the LOAD and leave the end of the cable to be tested open.
  3. Press Data Math then Data – Mem. The ripple in the measurement is removed. These minor imperfections in the cable should not be considered in the Cable Loss measurement.
  4. Use Averaging to remove random noise from high-loss measurements. Press BW 2 then Average.

 

The displayed trace shows the Cable Loss values in one direction through the cable. A Return Loss measurement would show the loss for both down the cable and back. Therefore, a Cable Loss measurement is the same as a Return Loss measurement divided by 2.

 

The average Cable Loss across the specified frequency range is shown on the screen below the graticules.

2-Port Cable Insertion Loss Measurements

A 2-port Insertion Loss measurement is used to measure the loss through a DUT (device under test) – or cable – over a specified frequency range. The FieldFox signal source is transmitted out the RF OUT connector, through the DUT, and into the RF IN connector. Both ends of the DUT must be connected to the FieldFox, either directly or indirectly using the cable used in the normalization cal.

 

‘Insertion’ loss simply means loss through a device, usually expressed in dB. It is exactly the same measurement as “S21 Transmission” in NA Mode.

 


 

Exception: In CAT mode, if the TDR data are saved in S1P format, the values represent the real part of the complex transform; the imaginary part is set to zero. To obtain complex data, either as real/imaginary or magnitude/phase pairs, use NA mode.

 

2-port Insertion Loss measurements are generally more accurate than 1-port Cable Loss measurements.

 

How to make a 2-port Insertion Loss Measurement

 

When measuring very long lengths of cable, it may be necessary to increase the sweep time. Learn how on page 62. Learn more in the Supplemental Online Help at: https://rfmw.em.keysight.com/wireless/helpfiles/FieldFoxOnlineSupplementalHelp/Home.htm.).