quote:

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> Hi guys!
> i have this difficult question that i cannot solve:
> how is measured the elctric field for the radiated emissions (Re102)?
> is it the root mean quare or the peak value? and supposing that the
> electric field is measured with one of these values, how these
> definitions can be apllyied if the receiver has a bandwidth in which
> many frequencies can pass through?
> therefore i would like to know what the dwell time and the "Minimum
> Measurement Time Analog Measurement Receiver" are.
> thank you very much in advance!
>

quote:

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> "mike" <michele.apuzzo@libero.it> wrote in message
> news:1120857514.557057.228880@z14g2000cwz.googlegroups.com...
>
> Mike:
>
> The US MIL-STD-461E has extensive explanations of detector functions,
> bandwidths and calibrations in the beginning paragraphs of the document.
> Also, Appendix A gives you a background discussion of the issues defined in
> the main body of the document. 461 is available only in English, but it is
> online and free.
>
> All 461 emissions are measured with a true peak detector. Further, 461
> defines the measurement bandwidths that must be used. (Common spectrum
> analyzers often don't have the exact impulse bandwidth required; HP used to
> customize HP-8566B analyzers specifically for 461 testing.)
>
> The dwell time is applicable to analyzers that are tuned in steps. If you
> command an analyzer to tune to a certain frequency, then it is supposed to
> dwell on that frequency, with it's detector open, for a minimum amount of
> time until it is commanded to move to the next frequency. If all real-world
> signals were continuously present at a constant amplitude, the dwell time
> would only need to be as long as the analyzer detector time constant (and
> peak is a very fast detector). However, the dwell time is a compromise
> value, designed to allow for a reasonable "probability of intercept" of
> real-world emissions. Imagine how long you would need to dwell at any given
> frequency if your device under test only did a chirp of output for 5
> milliseconds every 10 seconds. (Slightly longer than 10 seconds, to be
> sure.)
>
> The "minimum measurement time" is a similar concept for analyzers that have
> a true analog swept frequency range. Think of this as a "speed limit" to how
> fast you can move the resolution bandwidth across a given amount of MHz.
>
> The above comments apply to ALL 461 emission measurements, not just RE102.
> The analyzer / detection system doesn't need to know what type of transducer
> you are using; all transducers will be putting a voltage across the 50-ohm
> load of the receiver. (Using the transducer's correction factor, or transfer
> function, you correct the indicated dBuV to dBuV/m or dBpT or whatever.
>
> Regards,
>
> --
> Ed
> WB6WSN
> El Cajon, CA USA

quote:

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> Thank you very much for your reply!
> but i have still something that is not clear...
> what is a "true peak detector"?
> i mean... if i have a bandwith, for example 100kHz, there will be many
> frquencies passing through that, so putting a peak detector it will
> provide the envelope of the signal made up of those frequencies. Am i
> right or i am missing something?
> Moreover i read the MIL and i saw that in a paragraph states that the
> Electric field is measured with the "equivalent RMS", maybe this
> confirms what you told me...but indeed is the first time that i heard
> the existance of an "equivalent RMS". Would you be so kind to remove
> all this fog?:-)
> Regards,
> mike

quote:

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> "mike" <michele.apuzzo@libero.it> wrote in message
> news:1121204261.064127.29140@g43g2000cwa.googlegroups.com...
>
>
> Responding to the bandwidth question:
>
> Practically, it doesn't make any difference. The standard defines the
> measurement bandwidth that shall be used at any test frequency. What you get
> is what you get.
>
> If you measure a signal with some arbitrary bandwidth, you may not be
> capturing all of the power from that signal because the occupied bandwidth
> of the signal could be wider than the passband (your resolution bandwidth).
> If you increase the bandwidth, and the indicated signal amplitude also
> increases, then you know that the first bandwidth was inadequate. You keep
> increasing the bandwidth until the signal stops increasing (or you run out
> of wader bandwidths).
>
> You can see the mirror of this effect with viewing a fairly narrow signal.
> As you reduce the resolution bandwidth, the signal amplitude remains
> constant (although the noise level decreases). On a spectrum analyzer, you
> will be forced to use slower sweep speeds to maintain a calibrated display.
> Commercial EMI testers see this all the time when they do a pre-scan with a
> Peak detector, and then look at selected portions of the scan with a
> Quasi-Peak detector. They must sweep much slower with QP.
>
> When the standard moved from Revision C to Revision D, the
> narrowband/broadband differentiation was deleted, and new limits were
> formulated around standardized measurement bandwidths.
>
> Responding to the amplitude question:
>
> A Peak detector responds to the peak of a signal, whether the signal be a
> sine wave, a square wave or some unique pulse shape. To make the explanation
> simple, consider a sine wave with a 2 V peak to peak amplitude. The wave
> also has a Peak amplitude of 1 volt, and an RMS value of 0.707 volts. The
> calibrated EMI meter would display this signal as an amplitude of 0.707
> volts. (In a logarithmic scale, the Peak would be 120 dBuV, while the RMS
> value would be 117 dBuV.)
>
> If you had a 5 uS pulse that had a Peak of 1 volt, this signal would also be
> displayed as 117 dBuV (the RMS of a sine wave with the equivalent peak
> amplitude).
>
> Hope this helps; it's hard enough explaining this in English.
>
> --
> Ed
> WB6WSN
> El Cajon, CA USA