From FCC Part 15, ยง 15.33 Frequency range of radiated measurements.
(1) Except as otherwise indicated in paragraphs (b)(2) or (b)(3) of this
section,**for an unintentional radiator, including a digital device, the
spectrum shall be investigated from the lowest radio frequency signal
generated or used in the device, without going below the lowest
frequency for which a radiated emission limit is specified*, up to the
frequency shown in the following table: **
*
Highest frequency generated or used in the device or on which the device
operates or tunes (MHz) Upper frequency of measurement range (MHz)
Below 1.705 30.
1.705--108 1000.
108--500 2000.
500--1000 5000.
Above 1000 *5th harmonic of the highest frequency or 40 GHz, whichever
is lower.*
_/(emphasis added)/_
Since Part 15 requires no radiated test for digital devices below 30 MHz
there's no need to test real-time clocks at their fundamental frequency.
Cortland Richmond
On 7/5/2012 1112, Mcburney, Ian wrote:
Dear Colleagues;
I am trying to establish the maximum measurement frequency for
radiated emissions for a digital device that is an unintentional
radiator (part 15).
Is it set by the highest frequency generated internally in a
microprocessor or DSP or is it the maximum frequency that is tracked
"chip to chip" on a PCB.
Some of our components have high frequency internal clocking relative
to PCB tracked clocking.
Thank you in advance
*Ian McBurney*
*Design Engineer*
**
Allen & Heath Ltd
Kernick Industrial Estate
Penryn, Cornwall
TR10 9LU
United Kingdom
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