86118A Remote Sampling Head Module
Starting with firmware release A.06.90, 86100D Compatibility mode is no longer being actively tested and supported.
The 86118A electrical plug-in module provides remote sampling heads and measurement channels, for the instrument mainframe. Each of the remote heads of the 86118A utilizes 1.85 mm connectors (1 mm connectors for option H02). This module scales the input signal, sets the bandwidth of the system, and allows the offset to be adjusted so the signal can be viewed. The output of the module is an analog signal that is applied to the ADCs on the acquisition boards inside the mainframe. It is not recommended to use the 86118A with the 11898A extender module.
The 86118A remote heads contain the sampling electronics. The remote heads can be placed up to two meters from the instrument mainframe. This design makes it easy to connect to probe stations or the device under test (DUT) with very short or no cabling. By using a reduced amount of cabling, measurement degradation is minimized. The result is more accurate high-speed electrical measurements.
The 86118A plug-in module provides two accurate measurement channels with user selectable 50 or 70 GHz bandwidths. The amplitude and phase frequency response of both channels provide wide bandwidth, and high-fidelity time domain response. The lower bandwidth mode provides excellent oscilloscope noise performance for accurate measurement of small signals. The high bandwidth mode provides high-fidelity display and measurement of very high-speed waveforms.
The 86118A's RF inputs are very sensitive to ESD. The 1.85 mm RF connectors require special care.
The minimum required 86100-series firmware version for this module is A.03.03.
86118A Calibration
Unlike other modules, always attach a connector saver or cable to the input connectors before calibrating an 86118A. Do not provide any signal. Because each remote head's sampler is located near the input connector, this technique improves calibration accuracy by increasing thermal stability and by eliminating sampler reflections as explained in the following text. The mass of the cable or connector saver affects the sampler thermal equalibrium of your test setup. Even small temperature changes during calibration can affect sampler bias levels which in turn affect bandwidth and amplitude accuracy. Every time a sampler fires, it sends a small amount of energy toward the remote head's input connector. This is normal and common in all instruments that employ a sampler directly connected to the input. Without a connector saver or cable connected, this energy reflects back so quickly that it affects the sampled calibration value. Any cable ≥1 inch (2.54 cm) long or even an 86118A-101/2/3 connector saver, sufficiently extends the round trip time to eliminate this issue. It is not necessary to terminate the far end of the cable or connector saver.
In the module calibration dialog, a positive ΔT value indicates how many degrees warmer the current mainframe temperature is compared to the temperature of the mainframe at the time of the last module calibration. For 86118A modules, a positive ΔT value indicates how many degrees warmer the current remote head temperature is compared to the temperature of the remote head at the time of the last module calibration.
Deskew Remote Sampling Heads on 86118A-H01 Modules
To automatically remove any difference in the electrical lengths between the two remote sampling head cables, use Auto Deskew located in the Differential Advanced Setup dialog. Option H01 adds hardware skew capability and software control features for users who need skew adjustment to measure eye diagrams of differential signals. The skew adjustment of the module is limited to about 215 ps per channel. The 86100D introduces as much as 65 ps of internal skew. This means that the maximum allowable skew between the input signals is 150 ps at the RF inputs to the two remote sampling heads. You can also manually enter horizontal skew for each individual channel using each Channel's Advanced Setup dialog box.
Before Using the 86118A Module
Please review the following information prior to using the 86118A module.
Stabilizing the Temperature
Each remote head represents a relatively small thermal mass and meets specifications over a ±5°C range from the last calibration temperature, measured by the internal temperature sensor and reported in the All Calibrations dialog. Factors other than the ambient air temperature will affect the operating temperature of the remote head. These factors include air currents and the temperature and thermal mass of objects in contact with the remote head. You must ensure the temperature of the 86118A module is stabilized prior to calibrating the module and making measurements. As with all plug-in modules, the temperature is stabilized after 1 hour of continuous operation. The preferred method to stabilize the temperature of the 86118A is to set up the module and remote heads in the configuration or fixture that will be used to make measurements. This includes connecting the device under test (DUT) to the remote heads.
The temperature, thermal mass, and thermal conductivity of the DUT will affect the internal temperature of the remote head. A DUT that is significantly different in temperature than the remote head will add thermal mass, which may increase or decrease the temperature stabilization time.
When the internal temperature is stabilized, disconnect the DUT and perform a module calibration. If you move the remote head to a location that is thermally different than the location in which it was stabilized, you will have to wait for the temperature to stabilize again, and then calibrate the module before making measurements. For example, if the remote head is placed on a workbench for an hour, and then mounted on a cool metal fixture to make measurements, the temperature of the sampling head will begin to drop, possibly out of the ±5°C range.
Identifying Thermal Equilibrium
To identify thermal equilibrium of the remote heads, choose All Calibrations from the Calibrate menu. The All Calibrations dialog opens. Click Modules. Each installed channel displays Cal ΔT. Note the ΔT value, and close the dialog. Wait one minute then open the All Calibrations dialog again. Note the new value for ΔT. If this value changes more than 0.5°C, the channel is not at thermal equilibrium. If the reported value is >5°C, the module will need to be calibrated.
For very high speed signals (for example, 10 ps edges), if thermal equilibrium has not been reached, the rising and falling edges will appear to move on the horizontal axis of the display screen. If during the one minute of elapsed observation time the remote head is not moved, but the displayed signal shifts to the left or right, the channel is not thermally stable. The remote head cable should be mechanically stabilized during this observation, otherwise the displayed signal may show some movement due to slight phase changes in the cable.
Secure the Remote Heads
You should secure the remote head so that mass of the cable will not pull the remote head off a benchtop or out of a test fixture. You can coil or fasten the cables with cable ties to ensure the remote head remains in a position in which there is no strain on the RF input cables and connectors. You can create a mounting fixture for the remote heads. On the remote head's side cover there are three screw holes for M3 size screws. These holes are provided for mounting the remote head to a test fixture. It is important to consider the thermal properties of the remote head when designing a fixture. Larger fixtures will increase the thermal mass of the remote head, which will increase the time the remote head takes to reach thermal equilibrium.
Figure. Remote Sampling Head with Mounting Holes (Not to Scale)
Stability of the Remote Head during Measurements
The remote head cable carries the high frequency content of the timebase signal. Changes to the physical shape of the cable (for example, bending or twisting) may horizontally skew the signal on the display screen. Changes in the shape of the cable cause variations in the effective electrical length of the cable, which translates directly to horizontal timing variations. This is important to be aware of when making jitter measurements. Vibration is similar to cable movement. Vibrating the cable may also horizontally skew the signal on the display screen. Temperature changes can also result in timing variations. A temperature change of 1°C theoretically results in an approximate 200 fs change in electrical length. This electrical length change is due to the thermal expansion and contraction of the remote head cable.
As with all microwave connectors, take extreme care to protect the 1.85 mm input connector. Torque forces in excess of 5 in-lbs (0.57 N-M) and any shear or axial forces on the 1.85 mm input connector must be avoided. (4 in-lbs for Option H02 1.0 mm connectors.) Use Keysight torque wrench part number 8710-1582. Always use two wrenches when connecting or disconnecting cables or devices from the 1.85 mm connector. Use one wrench on the 1.85 mm connector of the remote head, and the other wrench on the cable (adapter, attenuator, or DUT) attached to connector. If you over-torque the RF connector, the connector may unscrew from the remote head. This will require service. If a connector loosens from the remote head, contact an Keysight service center for repair.
Removing Module for Transport or Storage
Before removing the module from the mainframe, coil the remote head cables. This will reduce the possibility of dropping one or both remote heads.
Supplied Accessories
| Item | Description |
|---|---|
| 5962-5965 | DCA Keysight 86100 Series 1.85mm Connector Reference Manual |
| 86116-20010 | 1.85 mm shipping cap (qty 2) |
| 86118A-101 | 1.85mm (m-m) adapters (qty 2) - Default option |
| 86118A-102 | 1.85mm (m-f) adapter (qty 1) and 1.85mm (m-m) adapter (qty 1) |
| 86118A-103 | 1.85mm (m-f) adapters (qty 2) |
| 1.85 mm Connector Information |
Available Options
| Item | Description |
|---|---|
| 86118A-201 | 15cm 1.85mm rigid coaxial cable (qty 1) |
| 86118A-H01 | Provides <65 ps of channel skew and alignment capabilities within 150 ps. |
| 86118A-H02 | Front-panel input connectors are 1.0 mm. |
| 86118A-UK6 | Commercial calibration certificate with test data |