LAPLACE INSTRUMENTS RF300 User Manual - page 21
LAPLACE INSTRUMENTS LTD
RF300
USER GUIDE
Page 21
Note 2
CISPR15 gave the verification data as a plot of loop current in dBuA vs frequency for the standard test
signal (1V, open circuit voltage with a source impedance of 50ohm). This seems to be a straightforward
method, especially as the limits are quoted in dBuA, so it’s a direct correlation between the calibration
loop and the limits.
CISPR16 is essentially the same information, but presented differently. It specifies the relationship
between the source voltage (1V, as specified above) and the output current in the loop as measured by
the current probe. Note that the current probe has a transfer characteristic of 1V/A. The relationship
between volts and current is ohms, hence the use of dB(ohms) as the ‘validation factor’.
The result is therefore a conversion factor scaled in dB(
Ω
) to convert current to voltage,
CISPR16 defines the validation factor dB(
Ω
) = 20*log(Vs/Ii) where Vs is the source voltage and Ii is
the loop current.
Vs = 1V = 1,000,000uV
Under ‘old’ CISPR15, for Ii @ 100KHz = 46dBuA = 200uA
So the new CISPR16 value is 20*log(1000000/200) = 74 dB(
Ω
)
and
Old CISPR15 for Ii @ 30MHz = 29dBuA = 29uA
So the new CISPR16 value is 20*log(1000000/29) = 91 dB(
Ω
)
These calculations confirm the relationship between the CISPR15 plot and the CISPR16 validation
factor.
The plots in the standards assume a current probe with a 1V/A transfer function. Such probes are ‘active’
but provide a flat frequency response. The RF300 uses passive probes which have a non-flat frequency
response. This is not important if the probe is ‘inside’ the calibration loop and has a linear transfer
function with amplitude. These factors hold true for the probe that is used. So the RF300 antenna uses an
antenna factor correction to produce a calibration that agrees with the validation factor. This antenna
factor is supplied with each antenna, and is equivalent to the correction factors as supplied with all EMC
antennas, test cells, LISNs and other types of transducer.
Using the antenna factor data with the RF300 enables the output to be compared directly with the limits
as specified in EN55015.