It is my understanding that the "conversion factor" converts the voltage
reading on a 50 ohm receiver to the amperage reading directly. In other
words, 1dbuV *is* 1dBuA and already takes into account the 50 ohm input
impedance.
Sadly, all this was written before advancements in electronics occured. For
example, I designed and built a small portable magnetic preamp I use for
measuring magnetic fields. It has a 4 inch diameter air core coil, produces
1 V per microTesla over the frequency range of 5 Hz to 1 MHz with a noise
floor of around 5 nT (the noise coefficient is dropping as a function of
frequency and integrates over the bandwidth) so most of the noise energy is
around the 5 to 100 Hz range. It was originally designed to address the
Swedish MPRII rules.
- Robert -
Robert A. Macy, PE [email protected]
408 286 3985 fx 408 297 9121
AJM International Electronics Consultants
619 North First St, San Jose, CA 95112
-----Original Message-----
From: KC CHAN [PDD] <[email protected]>
To: [email protected] <[email protected]>
List-Post: [email protected]
Date: Friday, January 04, 2002 8:57 PM
Subject: Magnetic measurement per CISPR 15
>
>Hi all
>
>I got a question about the magnetic measurement per CISPR 15, it says that
the sensitivity of the current probe is 1V/A.
>
>My interpretation is that X dBuV measurement you got from the EMI
receiver, corresponding to XdBuA, which is then compared to the limit, say
88dBuA at 50 kHz for 2-m 3-loop system. The manual I have says the same
thing. Is it correct?
>
>My question is
>1) Do we need to covert the voltage to current taking consideration of the
50 Ohm impedance of the receiver? If that is the case, we need to minus 34
dB from my voltage measurement to get the current measurement .
>
>2) In what ways the whole system has considered the impedance variation of
the current probe impedance. I have checked the impedance of the current
probe, the impedance is ranging from 40+ Ohm at 10kHz to 150+ Ohm at around
150K and decreases to around 75 Ohm at 1 MHZ.
>
>Thank you
>KC Chan
>
>
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