Specifications

PL 3120/PL 3150/PL 3170 Power Line Smart Transceiver Data Book 187
Conducted Emissions Testing
Each PL Smart Transceiver reference design has been demonstrated to comply with both FCC Section 15.107 “Limits
for carrier current systems” [1] and CENELEC EN 50065-1 “Signaling on low-voltage electrical installations in the
frequency range 3kHz to 148.5kHz” Part 1 “General requirements, frequency bands and electromagnetic disturbances”
[2].
Measuring the conducted emissions of a power line transceiver places extreme demands on the dynamic range of the test
equipment and even many of the most expensive EMI receivers on the market do not have sufficient dynamic range to
make the measurement without producing measurement artifacts that can lead to false conclusions. The traditional
technique of adding input attenuation to prevent instrument overload, is often insufficient since the required level of
attenuation often results in a measurement noise floor that is above or very close to the regulation limits. Note that this
problem is compounded by the fact that the overload indicator on many of these instruments fails to properly indicate an
overload condition when faced with burst like PL transmissions.
Both Rohde & Schwarz and Agilent (formerly Hewlett Packard) have acknowledged this problem and they each
recommend the use of a 150kHz high-pass filter at the instrument input to solve the problem. Rohde & Schwarz makes a
filter suitable for use with any measuring receiver “for conducted emission measurements in the presence of high long-
wave mains disturbance signals.” Use of this Rohde & Schwarz R&S EZ-25 150kHz high-pass filter (or equivalent) is
thus recommended.
Proper measurement of conducted emissions to verify compliance with FCC[1] and CENELEC EN 50065-1[2] requires
strict adherence to all of the following guidelines.
• Connect the product under test to the correct 50Ω//(50µH+5Ω) Line Impedance Stabilization Network (LISN)
as specified in CISPR Publication 16 [3]. Using a LISN that does not include the specified 5 ohm series resistor
may yield erroneous results.
• Connect a Rohde and Schwarz R&S EZ-25 150kHz high-pass filter (or equivalent) between the LISN and the
measuring receiver. Account for the filter’s 10dB pass-band loss when determining the measured result.
• Set the input attenuator of the measuring receiver to avoid instrument overload. This is accomplished by
measuring the emissions, then adding attenuation in the measurement path and re-measuring emissions. For
instruments that have a built-in input attenuator (and built-in compensation for that attenuator) the reported
levels should not change when the attenuation is changed. If there is an overload problem the indicated level
will change.
• Verify that the residual noise floor of the entire measurement setup remains at least 10dB below the regulation
limit once the appropriate attenuator is installed. Thus the corrected noise floor with all attenuators in place
should be < 38dBµV for FCC measurements, and < 36dBµV for CENELEC EN 50065-1 measurements.
• Use proper quasi-peak and average detector settings as specified in CISPR Publication 16. Although a
measurement scan with a peak detector is common, because it can be performed quickly, the limits specified by
FCC Section 15.107 and by CENELEC EN 50065-1 are for quasi-peak and average detectors only (for power
line transceivers, peak measurements are frequently higher than the required quasi-peak limits).
• Perform the measurements with the proper specified measurement bandwidths of 200Hz for frequencies below
150kHz and 9kHz for frequencies above 150kHz.
While most EMI receivers and spectrum analyzers do not have sufficient dynamic range to measure the emissions of a
power line transceiver without the addition of a highpass filter, two samples of the older Rohde & Schwarz ESHS30
EMI Receiver have been found to have sufficient internal dynamic range and filtering to make the measurement without
adding an external filter. Note however that the algorithms for “automatic” input attenuation on this instrument are
confused by burst like power line transmissions. The proper attenuation must be selected using manual mode. A set-up
program to accurately run scans for CENELEC EN 50065-1 compliance using the Rohde & Schwarz ESHS30 is
available from Echelon's Downloads page at www.echelon.com/downloads in the Transceivers category.