http://www.ieee-pses.org/symposium
http://www.emc2004.org/
From: George Bittar [mailto:[email protected]]
Sent: Tuesday, August 10, 2004 4:39 AM
To: [email protected]; [email protected]
Subject: Re: Selective Frequency Power Meter
http://www.ieee-pses.org/symposium http://www.emc2004.org/
Actually, I am not trying to measure de carrier, but the 1KHz
modulated AM at 80% signal!
So, I have to measure selectively the 1KHz signal at the terminals
of the equipment in order to know if the equipment is DEMODULATING the
signal.
The power level of 1KHz signal cannot be higher than -40dBm for my
application.
I have to mesure the behavior of this signal and trace it against
the carrier, which goes from 150KHz to 80MHz for 61000-4-6 and 80MHz to
1GHz;1.4GHz to 2GHz for -4-3, and I'm sure you all know that! :-)
Is it clear now? The point is not the signal I am generating, but
the signal I am demodulating.
Regards
George
George:
It's best to assume that I know very little.
Your problem seems to have changed from measuring RF power of an immunity
signal to measuring the response of the EUT. You describe that you want to
determine if the EUT is "demodulating" the applied modulated RF field. And
you want to measure this at "the terminals of the equipment."
You still haven't told us what the EUT is, so I'll use a consumer AM radio
receiver as an example. If you apply a modulated RF field, swept over a wide
frequency range, the receiver may exhibit both expected (as you cross the
operational channel) and unexpected (responses at undesired frequencies).
Since you are not trying to verify the resistance to jamming, then we can
forget about responses to RF on the Fundamental frequency.
So out-of-band signals may create responses in the EUT. And these responses
will be presented as audio output (frequently applied to an 8-Ohm speaker).
You defined a response criteria of "1KHz signal cannot be higher than
-40dBm."
The first thing you need to define are the units; dBm is a measure of power,
and the system impedance must be defined. Are you talking about dBm in 600
Ohms (audio standard) or in 50 Ohms (RF standard)? -40 dBm in 50 Ohms is +67
dBuV, or about 2.2 millivolts rms. This is an easy measurement for a decent
oscilloscope. However, -40 dBm in 600 Ohms is 0.0000001 Watts, which yields
a voltage of about 7.7 millivolts rms.
Assuming that other noise on this output is very low, you could also do this
test with a good rms millivoltmeter.
Going beyond this problem, I don't understand what you mean by "trace it
against the carrier." This may just be a linguistic perspective problem;
perhaps you are trying to say that you need to correlate the measured 1 kHz
output with the frequency of the applied field, simply to know what field
frequencies produce undesired 1 kHz responses.
The easiest way to do this in a manual immunity system is to just stop the
sweep whenever you get a response that exceeds your failure criteria and
look at the sweep generator displayed frequency.
Regards,
Ed
Ed Price
[email protected] WB6WSN
NARTE Certified EMC Engineer & Technician
Electromagnetic Compatibility Lab
Cubic Defense Applications
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Is Our Specialty
This message is from the IEEE Product Safety Engineering Society
emc-pstc discussion list.
IEEE PSES Main Website: http://www.ieee-pses.org/
To post a message send your e-mail to [email protected]
Instructions for use of the list server:
http://listserv.ieee.org/listserv/request/user-guide.html
List rules: http://www.ieee-pses.org/listrules.html
For help, send mail to the list administrators:
Ron Pickard: [email protected]
Dave Heald: [email protected]
For policy questions, send mail to:
Richard Nute: [email protected]
Jim Bacher: [email protected]
All emc-pstc postings are archived and searchable on the web at:
http://www.ieeecommunities.org/emc-pstc
