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Ed Price wrote:
.... What detector do you think should be used to evaluate the interference potential of BPL? I had thought that the QP detector was designed to the "annoyance" effect to AM or SSB modulation. CISPR has standardized this detector, and it's been adopted for many legal compliance standards world-wide. Yet the USA & British military insist on use of a Peak detector. Perhaps a dual level is needed, with a QP value for comparison of harm to the older analog modulation techniques, and a Peak value, for comparison of harm to digital modulation techniques. I understand that the CISPR 16-1 QP detector and 9KHz bandwidth are rooted in a series of subjective listening tests done somewhere around the 1930s. (cue storyteller here...) Firstly, the bandwidth survives, and you are right that it is embedded in all sorts of EM standards. I understand that part of the tests I referred to was to discover a instrument response that fitted well with subjective assessment of the impact of interference (I presume on an AM broadcast transmission). I think EMC measurement equipment often contains some of Average, RMS, QP and Peak detectors. I have seen several recent reports on BPL radiation that have not used the QP detector and the reasons have IIRC been that on a scan in xyz planes over a wide range of frequencies, the EMC receiver is too slow using the QP detectors. Ed Hare suggests that the AGC on a receiver acts similarly to the QP detector, and he is probably right. So the effect being that in an impulse noise scenario, your receiver will reduce gain roughly in line with the QP value (rather than say the RMS or the Peak), so it may be a good measure of gain reduction due to interference. As to interference with the detection process, the subjective tests to arrive at the QP detector did not assess impact on digital modulation. It seems to me that the impact on digital modulation / encoding systems would depend on the peak value / repetition scenario in concert with the encoding system's capacity for error detection / correction, but that is just me thinking aloud. Measurement bandwidth and extrapolation / interpolation is an issue, and possibly a bigger one than the detector response. Again there is a disconnect between 9KHz MBW (below 30MHz) for the standards and the 2KHz wide receivers in use for SSB. In my opinion, there is no better way to demonstrate the impact of interference in a 2KHz wide receiver than to measure it on a 2KHz wide receiver, so I suggest that (for us amateurs) there may be value in measuring both where possible. Owen |
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