OFCOM report on PLT's (Home Plug Networking)
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From: Jeff Liebermann on 29 Jun 2010 12:34 On Tue, 29 Jun 2010 08:50:35 +0100, Bob <bob(a)invalid.invalid> wrote: >If there is no "Transmission" then what do receivers detect? Nothing. More bluntly, if there's no transmission, adaptive smart notching simply doesn't work. >I haven't seen any specs regarding the Rx sensitivity for these "smart >notch" filters but they did say "encouraging results that shortwave >radio stations were received" so they must have agreed some form of >"threshold" level. Translation: You don't get to see the test results because they were all over the map, probably random results, and required considerable guesswork to call the results "encouraging". I don't have the spec but my guess is that it shouldn't be difficult to make a fairly strong RF signal run a frequency counter. I'll see if I can find the specified field strength. >> There's no interfernce between BPL/PLT and POTS phone service. >> >My broadband is on the POTS line Congrats. You have DSL, not BPL or PLT. >and the "mains sockets" refer to the >electric supply in the UK. My broadband/phone at the moment interferes >with my newly installed burglar alarm causing it to give a line fault >indication every time I use the phone and the installer is going to have >to reset the noise threshold level on the line so that I don't get >plagued by text messages. I will be interested to see if there is a >similar effect using "Homeplug" devices. Different issue and a rather muddled description. There is nothing in your description that involves the power line. My guess(tm) is that you don't have a proper DSL filter installed seperating the POTS (plain old telephone service) audio from the DSL signal, or it's mis-installed, or mis-wired. In the USA, alarm circuits require a RJ-31X/RJ-38X filter. <http://ww2.pulseeng.com/products/datasheets/EX137.pdf> If your alarm circuit doesn't have one of these, you're doing something wrong. -- Jeff Liebermann jeffl(a)cruzio.com 150 Felker St #D http://www.LearnByDestroying.com Santa Cruz CA 95060 http://802.11junk.com Skype: JeffLiebermann AE6KS 831-336-2558
From: Bob on 29 Jun 2010 12:52 On 29/06/2010 17:34, Jeff Liebermann wrote: > > Different issue and a rather muddled description. There is nothing in > your description that involves the power line. My guess(tm) is that > you don't have a proper DSL filter installed seperating the POTS > (plain old telephone service) audio from the DSL signal, or it's > mis-installed, or mis-wired. In the USA, alarm circuits require a > RJ-31X/RJ-38X filter. > <http://ww2.pulseeng.com/products/datasheets/EX137.pdf> > If your alarm circuit doesn't have one of these, you're doing > something wrong. > > > My alarm circuit does have a hard wired filter, however according to the installer there was a known issue with "noise levels" on broadband connections as speeds increased, I currently get about 7Mb download, which meant the threshold on the alarm cct. needed to be increased. He was here this afternoon and reprogrammed the controller settings and now everything works as it should including all text notifications. My muddled description. My phone/broadband sockets, qty5, and electric skts/wiring are close together and as far as I can tell for 4 rooms the cables run run parallel to each other and are only a couple of inches apart so when I have time I will install a couple of Homeplug units and see if I pickup any interference to either the broadband connection or an increase in noise to the alarm. The modem/router is at the end of the phone cable run.
From: Bob on 29 Jun 2010 12:57 On 29/06/2010 17:34, Jeff Liebermann wrote: > On Tue, 29 Jun 2010 08:50:35 +0100, Bob<bob(a)invalid.invalid> wrote: > >> If there is no "Transmission" then what do receivers detect? > > Nothing. More bluntly, if there's no transmission, adaptive smart > notching simply doesn't work. > I have probably misunderstood the concept but surely once a transmissions is received then that frequency is notched out for a given period of time and the "notch" is not automatically removed on cessation of the transmitted signal.
From: Bob on 29 Jun 2010 14:42
On 29/06/2010 17:57, Bob wrote: > On 29/06/2010 17:34, Jeff Liebermann wrote: >> On Tue, 29 Jun 2010 08:50:35 +0100, Bob<bob(a)invalid.invalid> wrote: >> >>> If there is no "Transmission" then what do receivers detect? >> >> Nothing. More bluntly, if there's no transmission, adaptive smart >> notching simply doesn't work. >> > > I have probably misunderstood the concept but surely once a > transmissions is received then that frequency is notched out for a given > period of time and the "notch" is not automatically removed on cessation > of the transmitted signal. Not quite what I expected. "In [Schw_08d] two criteria or thresholds are given, when a broadcast receiver is defined to be receivable: � Criterion (1): 14 dB above the noise floor. It is 3 dB lower than the desired SNR of an AM receiver to understand voice (derived from the acoustical measurements above) and around 11 dB lower than that required by a normal DRM transmission (out of [ITUR_03]). � Criterion (2): the absolute threshold of -95 dBm which is derived from equation 13 For activation, a processing time of 15 seconds is conceded to PLT modems. If the two criteria were passed once, the notch shall be kept for at least 3 minutes. This timing hysteresis is a tradeoff between consumer acceptance listening to a fading broadcast service and the processing capabilities of PLT modems creating a notch. The timings were found by the STF332 [Schw_07a] during the plugtests where the concept was verified [Schw_08c] page 81 <http://www.ets.uni-duisburg-essen.de/download/public/Schwager_Andreas_Diss.pdf> |