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Re: Line Noise Interference Question



"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

>Am I right in assuming if it runs warm to the touch, it's probably a linear
>power supply and not a switching type?

Probably. But linear supplies may be cool depending on the design. Weight is
probably a more reliable indicator. A 60Hz power transformer is heavy
(relatively). A switching supply may have no transformer or one that is for
a much higher frequency which is usually quite light. Compare the
size/weight of the little transformers (silver rectangular cans) inside an
X-10 module with the heavy transformer inside a linear power supply.

>> Switching power supplies can cause problems for X-10 in two ways.
>>
>> 1. They can output noise in the 120kHz neigborhood (You've seen such noise
>> from a CFL.) which an X-10 receiver sees as continuous logical 1s at each
>> half cycle. This tends to jam all X-10 signals. (NOTE: An X-10 receiver
>> counts transitions in a 650µS window starting at ZC+250µS. 48 or more
>> transitions is a logical 1. See http://www.mbx-usa.com/xtc798.txt - first
>> paragraph.)
>
>I understand this part pretty well.  The "shouting in windy tunnel" effect.
> If there's a constant random signal present, it will render a structured
>signal of near equal strength unintelligible.  One way to overcome this may
>be with a repeater, which would in a sense act as a megaphone in the windy
>tunnel.

A repeater doesn't help if it also repeats the noise. It needs to
selectively repeat only the signal. Making every module an intelligent
repeater (i.e. Insteon) makes some sense as it fills the network with a
3.16V signal but it remains to be seen whether their implementation works as
advertised. They also have Insteon filters and repeaters so...

>> 2. They may filter their output to prevent noise from reaching the mains.
>> The filters may also filter 120kHz thus draining the X-10 signals.
>>
>> There's no easy way to tell whether a switching PS is X-10 friendly other
>> than trial and error. They seldom provide much information beyond
>> input/output voltage/current.
>
>I'm still pretty fuzzy on exactly how an X-10 filter can block both unwanted
>transmissions of noise and isolate signal sucking components as well.  Those
>seem like disparate functions.  From what I've read these X-10 filters
>perform the equivalent of unsoldering a capacitor from across the power
>leads.  I think I'll have to read up on the design of X-10 filters before I
>venture deeper into unknown waters and drown.

They block the passage of higher frequencies while allowing lower
frequencies through. There's no perfect analogy but you might view them like
a furnace filter which blocks large particles but passes small particles.
But, electronic filters don't get clogged.

>Would it be fair to say an X-10 filter plugs a hole in the X-10 network and
>that hole, before plugging, would let the X-10 signal "leak" out of the net
>and noise from something like a bad power supply leak into the net.  The
>tradeoff is that no good X-10 signals can reach beyond that point.

Yes.

>> X-10 specs are for 120kHz ±2kHz so most test equipment is designed around
>> that. With the relatively recent proliferation of switching power
>supplies,
>> currently available test gear may prove incapable of detecting all the
>> frequencies that will jam X-10.
>
>That's not heart-warming news.  I assume that an oscilloscope could detect
>that noise even though commercial X-10 testers won't.

You would need a real analog oscilloscope. A DSO (Digital Sampling
Oscilloscope) usually has low limits on voltage input levels. Its sampling
rate may be too low to accurately reproduce higher frequencies. It's
difficult to see a high frequency signal riding on the 60Hz as you cannot
lower the baseline and the 60Hz goes offscale before the gain is high enough
to see the higher frequency signal. You need to filter out the 60Hz and then
the characteristics of the filter have to be considered.

I'm not sure what ACT uses in their Scope-Test2. A schematic on their web
site shows a DIY version that merely uses a capacitor as a low-pass filter
to block 60Hz while passing higher frequencies. That should pass the
frequencies of interest but, if they use a bandpass filter, its bandwidth is
the crucial parameter.

>OK, professor.  I promise to do my homework.  I'll admit I got sidetracked
>by that copper.org detective story.  It's nice to know that even
>professional sparkies often take several tries to get to the root of the
>problem.  It was scary enough to make me wonder whether the person that said
>he saw better work from a DIY than from a licensed electrician was telling
>more truth than hyperbole.   I'll try to stay on point.  I may take a
>screwdriver to my ACT and X-10 filters to see what's inside.  I confess to
>having to actually tinker with something for it to make sense to me.

I believe you can see what's inside some of them on Ido Bar-Tana's site.

>> NOTE: If you follow the link in the first URL to the ATX power supply
>> schematic, the 220nF capacitor used across the mains presents 6 ohms
>> impedance to 120kHz.
>
>What sort of impedance levels should one be seeing around the house?  Is
>this a number that's going to vary from outlet to outlet?  What little I've
>read is that impedance varies depending on the signal frequency.  (I was
>just about to read some more when I realized this is exactly where I left
>the rails and got lost in tracing circuits in Columbus Ohio buildings . . .)

There's no simple way to measure. That's why I bemoan the loss of the web
site that had all the white papers on powerline communications. There are
network analyzers designed for testing 50/75 ohm coaxial networks. You can
buy one used starting at about 10K.

     http://www.testequity.com/products/227/

>I assume that simply removing such capacitors is not a good idea since that
>would likely change the power supply from a signal sucker to a noise
>generator.   I just wish there was was a better solution to the
>ever-widening number of devices that impinge on X-10.   If UPB can use an
>increased voltage, could an X-10 transmitter similarly put an increased
>voltage on the line.  I know it violates the EU Cenelec rules, but is it
>technically possible?  Would it interfere with other devices if the power
>was boosted beyond the 10V P to P of the current generation of devices?

Removing the capacitor _may_ turn it into a noise source. It depends on the
type of equipment. You may find capacitors on AV gear where the intent is to
block external noise from entering.

The effects of higher 120kHz voltages on other devices is unknowable. I
think it's a bad idea. I also think UPB's 40V noise pulses are a _very_ bad
idea that might cause problems for other gear.

>> A bandstop filter (e.g. all of the X-10 filters) deals with both noise and
>> the capacitor. It blocks noise from reaching the mains and blocks X-10
>> signal from reaching the capacitor.
>
>I'll have to Google on filters to understand more.  It seems the X-10
>filters are doing the electronic equivalent of removing the soldered in PS
>capacitor from the circuit.  I've got a pretty fair understanding of how
>SPS's create noise now.

No, the filter merely isolates (selectively, depending on frequency) the
part of the circuit that contains the capacitor from the part of the circuit
on the other side of the filter.

>> If it's a noise problem, the noise will be constant.
>
>I can only offer what I see on my ESM-1 when I leave it plugged it.  From
>time to time, for no apparent reason that I can discern, the first bar of
>the ESM-1 lights up steadily with no corresponding X-10 good LED.  It
>happened in the kitchen twice and the living room once.  I turned off every
>light in the house but the bar persisted.  It even came back after
>unplugging it but eventually it left as mysteriously as it came.  I am
>hoping the Monterey will be able to confirm that there's real noise on the
>line and not just a metering anomaly.

For a few weeks, I kept my ESM1 plugged into an outlet where it was visible
out of the corner of my eye whenever I was at my desk. I saw something
similar periodically for short periods and only at certain times of the day.
I did not investigate further. It may be a neighbor's device or maybe the
electric utility is experimenting.

>> It will not come and go in sync with the ZC in patterns that
>> repeatedly turn on selective lights in the middle of the night.
>> The X-10 noise fairy does that.
>
>The one thing the Lynx did show was how RF collisions (activating two
>different TM751's on different housecodes on different circuit branches via
>two different keychain remotes) created what they called "code fragments."
>Using B, F and D housecodes I was able to reliably generate code fragments
>that were for housecode M.  From what I can deduce, Marrick avoids using
>"Bad Start Code" by considering all start codes as good and then labelling
>what follows a good command or a code fragment based on whether it's
>complete.  If it's OK with you, I'll email a copy of the screenprint.

The ESM1 does more or less the same. If any 1110 is followed by a sequence
that appears to be valid X-10 (without any complex analysis), it lights the
"X-10 Good" LED. That's also the way X-10 modules work.

I'll try to look at the screenprint if you send it.


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