Brian- I think the answer is (as it is in so many cases): it depends. Look at my reply to Jim Hulbert for some examples of how 'it depends'.
As far as digital receivers, they will see interference from both CW and spread spectrum clocks. But the effects can be anything from negligible to stopping communications. For direct-sequence spread spectrum systems (e.g., CDMA cell phones), interference from either type of clock will be the same, assuming the total power is the same and the interfering signal is fully contained within the bandwidth of the receiver. An interesting example is CDMA, where the base station controls the power level of all the cell phones it is talking with so that at the base station all the cell phone signals it receives run at a standard bit error rate, about 1 in 100. If some interference comes along in the channel that increases the bit error rate, the base station will command the cell phones to increase power to get the bit error rate back down to about 1 in 100. (BTW, CDMA can run up to 30 cell phones in the same channel, with all the phones are transmitting continuously on the same frequency. The system is able to sort them all out, but that is another lengthy conversation). So the effect of any given spread-spectrum clock on any given remote toilet controller radio depends on the characteristics of both the spread-spectrum clock and the radio system. There ain't no easy answers to it all. All that is for sure is that spread-spectrum 'fools' the emissions measurement, which is looking for a certain amount of power (average or quasi-peak) within a given bandwidth, rather than total emitted power. The standards committees are well aware of what is going on and have been dancing around the issue for decades. I think there is movement towards looking at total emitted power, especially as EMC receivers progress to using wide total bandwidth FFT-based measurements. Donald Borowski EMC Compliance Engineer Schweitzer Engineering Labs Pullman, WA, USA From: "Brian Oconnell" <oconne...@tamuracorp.com> To: <EMC-PSTC@LISTSERV.IEEE.ORG> Date: 12/01/2011 09:25 AM Subject: RE: [PSES] Quasi-peak Sent by: emc-p...@ieee.org Good stuff, this empirical experience. But the question remains - does this spread-spectrum stuff, for a comparative power level, increase or decrease interference with my master-blaster 5000 remote toilet controller? One member said that it only will affect stuff that is very close to the operating freq and that the most digital receivers would not see it. But EMC amateurs such as me need MOAR empirical experience from Don and Ed and et al. For my employer's products, I am more concerned about customer complaints than demonstrated margin from some fantastical limit line in an EMC standard. Brian -----Original Message----- From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of don_borow...@selinc.com Sent: Thursday, December 01, 2011 8:58 AM To: Price, Edward Cc: EMC-PSTC@LISTSERV.IEEE.ORG Subject: RE: [PSES] Quasi-peak Ed- Given your scenario, you are right. However, in my experience of measuring radiated emissions of spread spectrum clocks, I have always noticed a decrease in not only the quasi-peak and average measurements, but the peak measurement as well. I think this may be due to the bandwidth of the spreading signal -- if it is wider bandwidth than the receiver bandwidth (120 kHz CISPR in my case), then there will be reduction in the peak as well. With a high bandwidth spreading signal, the RF will not spend enough time within the bandwidth of the receiver for the receiver to respond to the full amplitude of the signal. Donald Borowski EMC Compliance Engineer Schweitzer Engineering Labs Pullman, WA, USA From: "Price, Edward" <ed.pr...@cubic.com> To: <don_borow...@selinc.com>, <EMC-PSTC@LISTSERV.IEEE.ORG> Date: 12/01/2011 08:06 AM Subject: RE: [PSES] Quasi-peak Don: I think that the ?spread spectrum clock? works because of both the receiver bandwidth and the detector function. For instance, imagine a pure CW clock signal, and it is being hopped around in 1 kHz steps, all in the range of 10 kHz. Now imagine that a receiver with a 1 MHz resolution bandwidth is watching that signal. The indicated amplitude will be the same with Peak, QP & Average detectors. Because the hopping is always within the receiver bandwidth, the hopping has no effect. As the hopping stays within the receiver BW, each detector has plenty of time to reach the full amplitude of the signal. Now imagine that a hop starts well outside the RBW; the receiver sees nothing. Then the clock hops into the RBW, and each detector starts charging. Fifty microseconds later, the clock hops out of the RBW. You look at the three detectors, and the Peak reads, say 1.0. The QP might read 0.1, and the Average might read 0.0. The difference was all about how long the receiver had to observe the signal; all detectors ?saw? the same amplitude signal, but they could only report what their time constants allowed. Ed Price ed.pr...@cubic.com WB6WSN NARTE Certified EMC Engineer Electromagnetic Compatibility Lab Cubic Defense Applications San Diego, CA USA 858-505-2780 Military & Avionics EMC Is Our Specialty > -----Original Message----- > From: don_borow...@selinc.com [mailto:don_borow...@selinc.com] > Sent: Thursday, December 01, 2011 7:22 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: [PSES] Quasi-peak > > Spread spectrum clocks "work" due to the measurement bandwidth of the > receiver, so this effect holds for peak, quasi-peak, and average. > > > Donald Borowski > Schweitzer Engineering Labs > Pullman, Washington, USA - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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