Normally, two of these are required for compliance testing.įigure 7 – The Tekbox model TBLC01 5uH LISN fits in the hand. A DC LISN is mainly used for testing 24 to 28 volt military and aerospace equipment to MIL-STD-461 or DO-160 standards.
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It comes with binding posts for the DC in/out and comes with a nice instruction manual (available as a download here). The model TBLC08 LISN is a palm-sized rectangular box (Figure 7). The aqua trace is the ambient noise level. Note the emissions exceeds even the FCC Class A test limit. This unbranded unit does not include a line filter and the results are obvious! This is a good reason to stick with well-known manufacturers.įigure 6 – A measurement of an inexpensive unbranded “wall wart” power supply. I also measured a low cost “wall wart” switching power supply (Figure 6). The attenuator is much more lossy below about 200kHz. At the higher frequencies, it indeed appears to be a 10 dB difference (Figure 5).įigure 5 – A comparison of the neutral circuit with (violet) and without (yellow) the 10 dB attenuator. To Tekbox’s credit, they spec the attenuator performance from 150kHz and higher. I also tested the 10dB attenuator (Figure 5) and found it to be more like 14 to 26 dB of loss below about 200 kHz. The balance between the two is very good.
We’re looking from 9kHz to 30MHz, so emissions below 450kHz should be ignored for commercial equipment.įigure 4 – Measurement of the line (yellow) and neutral (violet) emissions. The green display line is approximately at the FCC Class A limit. Both produced very similar results.įigure 3 – The system under test included a Keysight MSO-X 3102A oscilloscope and Rigol DSA815-TG spectrum analyzer.īoth line and neutral measurements appeared well balanced (Figure 4). I also compared the results with an EMCO 3810/2 LISN of similar specifications. However, testing the general performance and signal balance was sufficient. Thus, the results may differ somewhat from a normal compliance test. Note that for the purposes of this review, I did not test over a ground plane or in a shielded chamber. I set up the system to measure a typical switching power supply in an Keysight MSO-X 3102A oscilloscope (Figure 3). The left-hand circuit board attached to the front panel includes a 10dB attenuator, along with the 150kHz high pass filter and transient limiter. The interior is laid out neatly and all components appear to be the highest quality (Figure 2). The artificial hand is designed for 220pF and 511 Ohms and the impedance is 50 Ohms with the standard 50uH and 5 Ohm design as specified by CISPR 16.įigure 2 – The Tekbox TBLC08 LISN was built using high quality components. The unit meets IEC 61010-1 for product safety. The frequency range is 9 kHz to 30 MHz, can handle up to 240V / 50-60Hz, and up to 8A of current. There are fuses for both the line and neutral circuits.į igure 1 – The Tekbox model TBLC08 is enclosed in a well built enclosure. The rear panel has a large grounding braid included and a standard IEC power line receptacle. The review unit had the normal NEMA 5-15 connector for U.S. The test power connector may be customized for different worldwide locations. The transient limiter can help protect your analyzer from harm. Turning power on/off on the unit under test or switching the LISN from line to neutral can create large transients that can destroy the sensitive front end circuitry of spectrum analyzers. It also includes a 150 kHz high pass filter to reduce lower-order power line harmonics, as well as a 10 dB attenuator and transient limiter, which is a great addition and missing on most other LISNs. The product seems well built and has all the usual controls Line-Off-Neutral control, Earth inductor In/Out, power switch, RF output port, and an artificial hand connection. It comes with a line cord, coaxial cable with N-to-BNC connectors, and a nice instruction manual (available as a download here). The model TBLC08 LISN is about the same size as a very small printer (Figure 1). I’ll be reviewing their model TBLC08 (line-powered 50uH LISN) and model TBOH01 (DC 5uH LISN). Tekbox Digital Solutions recently introduced LISN models for both line-operated and DC-operated equipment. This is normally done using a spectrum analyzer (or EMI receiver) and a line impedance stabilization network, or LISN, which helps match the power line to 50 Ohms.
While radiated emissions is the usual nemesis for product designers and EMI engineers, it’s also useful to have a way to measure conducted emissions. EMI emissions testing includes both radiated and conducted.