Fixturing issues
Connecting the HP 4380A test set to various devices-under-test
(DUTs) requires that the user assemble an appropriate fixture.
Some of the important considerations in making these connections and fixtures are discussed below. Sources for components for building fixtures are also listed.
Crosstalk crosstalk are important when the connections are close together.
One solution for 4-pair, near end only testing is an experimental fixture from HP, part number
04380-65001. This fixture has shields and push pins for quick connect to the DUT leads. It requires 150ps port extension value due the effect of the pin dimensions. (This experimental fixture is sold as a replacement part from HP and has no specifications.)
Fixture materials/design
To minimize crosstalk between pairs, the length of any untwisted
DUT leads should be minimized.
In addition, shields can be added between pairs to reduce RF crosstalk coupling.
The sample fixture supplied with the system (w-shaped fixture) is for near-end and far-end testing of a 2-pair balanced cable. It has high crosstalk isolation between the near and far ends, and small shields between the pairs at each end to reduce crosstalk.
This fixture is not ideal for a 4-pair near-end only test configuration as it requires too much exposed pair length to reach the connections. A better solution is a fixture where all 4 test port pairs are arranged close together so that DUT leads are short. Shields for reducing
Fixtures are normally made of copper or aluminum.
Experimental fixtures are easily made from copper-clad PC board material. It is easy to solder shields and make 1/4" holes for
SMA connectors and/or solder the
SMA connectors to the fixture ground plane. The goal is to have a good ground for RF signals and rigid connections for the DUT.
Calibration at the SMA connector is required, of course, so plan to leave enough room around SMA connectors to attach the flexible coax lines. If you calibrate directly on the DUT side of the
SMA, leave space to attach loads.
(see semi-rigid coax calibration below).
SMA connectors
SMA connectors are suggested to connect the coax cables to the
DUT. There are many kinds of
SMA connectors. By looking at a catalog of connectors, you can find various configurations that could match your fixture design.
Some users prefer to solder the
DUT for the best connection, while others use a slip-in pin socket (like an IC socket pin) or other socket that could be mated to a male or female SMA center conductor connection.
For calibration on the DUT side of the SMA (used with semi-rigid coax setups), the normal male or female screw-on connectors are used to match the SMA calibration standards. Then some adapters, with short electrical length, can be used to connect to the DUT and mate with the SMA center connectors. Port extension is used to correct for the adapter length, or a similar length is added to the calibration standards when calibrating.

Maintain 50 ohm transmission lines to the DUT
The calibration method and port extension features used with the
HP 4380S system assume that the cables from the 8-port test set
(HP 4380A) to the fixture (and
DUT) are high quality 50 ohm coax and are stable between calibration and measurement. The HP 4380S microflex (095) cables are high quality while still providing flexibility to attach to many different fixtures or DUTs. Other cables may be used, including semi-rigid coax (085), as long as they are high quality and 50 ohm impedance. For some very small
DUTs, micro coax and be used to extend from the calibration point
(SMA on a fixture) to the DUT.
These should be 50 ohms. To extend the calibration plane to the actual DUT connection, use port extension to add the electrical length of the micro coax extension cables.
Semi-rigid coax calibration
"USE EXT-STD" to use open/short/load on each SMA at the fixture. For through calibration, the "*QUICK
TYPE-B" selection is suggested.
Through calibration connections
When using semi-rigid coax, the through connections must be the same electrical length for use with the current system software. For an 8-port calibration, 4 through connections will be required.
These must be high quality semi-rigid coax or equivalent.
Four 6" lengths of semi-rigid coax that have the same electrical length (check using a network analyzer) bent in a U shape to allow slight bending to reach various through combinations have worked well for some fixture designs where the ports (SMAs) are positioned to be near each other. Good (matched) through calibration with semi-rigid coax and a rigid test fixture are required for good LCL (balanced to unbalanced testing) noise floor performance.
Sources of fixture materials*
With semi-rigid coax, a modification to the calibration process is suggested which requires independent calibration of each port at the fixture using open, short and load standards.
This eliminates the use of the build-in transfer standard in the
HP 4380A, but provides better calibration because no movement occurs between calibration and actual measurement.
Add the following line to your
HP BASIC program to modify the calibration method:
1086 CALL Printer_setup
1087 Svc6=1 <ADD THIS LINE
1088 Call Main_menu
(Line numbers may vary slightly)
After this change, the calibration softkey choices will include:
Copper-clad PC board material:
Radio Shack stores. 4.5 x 6.4 inch both sides copper clad. P/N: 276-1499A.
Contact local printed-circuit board fabricators.
SMA connectors, semi-rigid, microflex coax cables:
Pasternack Enterprises
Irvine, CA. 714-261-1920
M/A-COM Inc Interconnect Products Div.
Waltham, MA 617-890-4750
United Microwave Products
Torrance, CA 310-320-1244
Amphenol Corp RF/Microwave Opr
Danbury, CT 203-743-9272
* These suppliers are not endorsed by
Hewlet-Packard Co. They are listed as service to our customers.
For more information on Hewlett-Packard
Test and Measurement products, applications, or services please call your local Hewlett-Packard sales office. A current listing is available via the Web through AccessHP at http://www.hp.com. If you do not have access to the internet, please contact one of the HP centers listed below and they will direct you to your nearest HP representative.
United States:
Hewlett-Packard Company
Test and Measurement Organization
5301 Stevens Creek Blvd.
Building 51L-SC
Santa Clara, CA 95052-8059
(800) 452-4844
Canada:
Hewlett-Packard Canada Ltd.
5150 Spectrum Way
Mississauga, Ontario
L4W 5G1
(905) 206-4725
Europe:
Hewlett-Packard
European Marketing Centre
P.O. Box 999
1180 AZ Amstelveen
The Netherlands
Japan:
Yokogawa-Hewlett-Packard Ltd.
Measurement Assistance Center
9-1, Takakura-Cho, Hachioji-Shi,
Tokyo 192, Japan
(81) 426 48 3860 FAx: (81) 426 1073
Latin America:
Hewlett-Packard
Latin American Region Headquarters
5200 Blue Lagoon Drive
9th Floor
Miami, Florida 33126
U.S.A.
(305) 267 4245/4220
Australia/New Zealand:
Hewlett-Packard Australia Ltd.
31-41 Joseph Street
Blackburn, Victoria 3130
Australia
131 347 ext. 2902
Asia Pacific:
Hewlett-Packard Asia Pacific Ltd.
17-21/F Shell Tower, Times Square,
1 Matheson Street, Causeway Bay,
Hong Kong
(852) 2599 7070
© Copyright 1996
Hewlett-Packard Company
Data subject to change.
Printed 9/96
5965-5252E
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