: Ken Javor[SMTP:ken.ja...@emccompliance.com]
Sent: Tuesday, October 30, 2001 6:20 PM
To: umbdenst...@sensormatic.com; emc-p...@majordomo.ieee.org;
dmck...@corp.auspex.com
Subject: Re: The Trouble with Convention, The Final Chapter
Following your logic, I was just following
...@sensormatic.com; emc-p...@majordomo.ieee.org;
dmck...@corp.auspex.com
Subject: The Trouble with Convention, The Final Chapter
In the face of all the responses I and others gave last week showing the
MATHEMATICAL RULES for calculating logarithms and average and peak power,
and the rationale and math
...@corp.auspex.com
Subject: The Trouble with Convention, The Final Chapter
In the face of all the responses I and others gave last week showing the
MATHEMATICAL RULES for calculating logarithms and average and peak power,
and the rationale and math behind pulse desensitization calculations,
apparently
Subject: The Trouble with Convention
Date: Mon, Oct 22, 2001, 4:46 PM
Similarly, it appears the same issue of convention is the basis of certain
FCC clauses, for example, the reporting of the output of an averaging
detector as called for by 15.209 and other clauses for some frequency bands
Subject: RE: The Trouble with Convention
Date: Tue, Oct 23, 2001, 8:18 AM
Chris,
I don't believe we are addressing math proofs in this situation. Just as
the free space impedance of 377 ohms (51.5 dB) does not apply to the
reactive near field but is specified by ETSI for conversion from dBuV
Subject: RE: The Trouble with Convention
Date: Tue, Oct 23, 2001, 7:37 AM
Don,
The mathematical proofs to verify that 20log(D) is a valid method to
calculate the change in dBuV for a voltage signal with duty cycle D are
mathematically incorrect. There is no sanity check.
Multiplying D times V
The important thing is, first average the quantities, then convert to dB.
Ever seen folks doing video averaging on a log-scaled analyzer display?
Sure you have. And it's wrong. How wrong?
Take two samples, 100 dBq and 25 dBq. Sum their amplitudes in dB (100dBq +
25dBq= 125dbq) and divide by
For the FCC calculations, I can understand ...
E = I*R = 1uA*377 ohms = 377*10^-6 Volts
dBuV = 20log(377*10^-6V/1uV) = 51.5 dBuV
Assume you measure XuA's and you want to
convert to dBuV's.
E = I*R = XuA*377ohms = X*377*10^-6 Volts
and ...
dBuV = 20log[X*377*10^-6 Volts/1uV]
Pursue the right question and one might receive a meaningful answer.
How do you convert from dBuA to dBuV when measuring a 50 kHz signal at 10
meters? How do you convert from linear terms to log terms when addressing
the output of an averaging detector where the limit is field strength in
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