>-----Original Message-----
>From: scott....@jci.com [mailto:scott....@jci.com]
>Sent: Thursday, December 06, 2001 5:17 AM
>To: emc-p...@majordomo.ieee.org
>Subject: Stepping receiver, step sizes.
>
>
>
>Hello Group!
>
>I would like to ask a question regarding EMI Receiver step sizes in the
>higher frequency range.
>
> We are performing radiated emissions testing in a
>semi-anechoic chamber
>using an EMI receiver. We plan to cover a high frequency
>range between 1
>and 5 GHz (a large spanse to cover!). I would like to know
>what practical
>step size (ie. 8kHz or 20kHz or 80kHz) I could choose for such a wide
>range and keep:
> 1. The data accurate, meaning that I wouldn't be "missing" or
>stepping around energy by taking to large of a step.
> 2. Keep the amount of data I'm collecting to a
>reasonable amount so
>that I may process it (apply correction factors for antenna,
>cable loss,
>pre-amplifier).
>
>My question comes up primarily because I haven't found any
>specifications
>that require things like minimum scan time, maximum step size,
>or the like.
>
>Is anyone aware of a specification out there that covers this,
>or have any
>information/personal experience that could help me make a
>determination?
>
>
>Thanks for any help in advance!
>
>
>Regards,
>
>Scott Mee
>EMC Engineer
>
>Johnson Controls Inc.
>PH: 616.394.2565
>EMAIL: scott....@jci.com
>
>
Scott:
The issue of receiver bandwidth, step size and dwell time is covered in
detail in Section 4.3.10 of Mil-Std-461E. I know that this is applicable
only to military requirements, but it's a good example. In the 1 GHz to 5
GHz range, they call for a 6 dB resolution (or IF) bandwidth of 1 MHz. If
you are using an analog swept receiver, then the maximum sweep speed is 15
seconds per GHz. (Remember this is using a peak detector, so you may need to
sweep slower if you are using a QP or average detector.) If you are using a
receiver which is tuned in discreet "hops", your maximum hop size must be
one-half bandwidth (which would be 500 kHz). And you must dwell at each
measurement frequency for 15 milliseconds.
These are the minimums. Many times I have to test devices which have a low
duty cycle, and this brings up the problem of "probability of intercept."
For example, if I try to find the fifth harmonic of a transmitter that sends
a 20 millisecond data burst once every 10 seconds, then I have to increase
the dwell time to be sure that I dwell long enough (more than ten seconds)
at each measurement frequency for the event to occur.
As for the amount of data acquired; just let the software do the work. Write
(or buy) software which ignores unimportant data, but highlights the "top
100" emissions or whatever. The software I use can handle tens of thousands
of data points, but "filters out" the many thousands of relatively useless
points between the important peaks. And the software should also be doing
the work of adding correction factors.
(461E also includes a discussion of immunity sweep speeds.)
Regards,
Ed
Ed Price
ed.pr...@cubic.com
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Services Is Our Specialty
Shake-Bake-Shock - Metrology - Reliability Analysis
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