UNH-IOL accounts for FR4 effects on test jigs

FR4 can introduce loss on technologies that operate near or above 1 GHz.

-- Test & Measurement World, 12/15/2011 3:47:07 PM

The UNH-IOL (University of New Hampshire InterOperability Laboratory) designs and builds its own test jigs to connect test equipment with devices under test. The staff makes its test jigs out of FR4 material, and for a jig used with data communications products, they must compensate for the fact that FR4 can introduce loss on technologies that operate near or above 1 GHz.

For 1000BaseT PMA (physical media attachment) testing (IEEE 802.3 Clause 40), the UNH-IOL uses a test jig that converts an Ethernet jack to SMA connectors in order to test a 1000BaseT transmitter on an oscilloscope. To correlate the measurements of this signaling to those of implementers and other labs, the UNH-IOL staff had to characterize the loss of the 1000BaseT PMA test jig. They found the loss by measuring the differential insertion loss using a network analyzer, and despite the short length of trace used and a jig design created with good engineering practices, the loss was over 0.5 dB. This amount of loss could cause miscommunication between engineers at two different laboratories and could slow attempts to correct the underlying issues.

 In this example, the UNH-IOL found that the differential insertion loss was between 300 kHz and 200 MHz. The staff now applies this loss during the postprocessing of measurements to eliminate the effects of the jig. www.iol.unh.edu

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This news was originally reported in the "Testing the Limits" blog on our site.