Re: Line Noise Interference Question

["Robert Green" <ROBERT_GREEN1963@xxxxxxxxx>]

"Dave Houston" <nobody@xxxxxxxxxxxx> wrote in message

> You're over complicating things and looking at the wrong factors.

No doubt!  But thanks for taking the time to offer guidance anyway.

> Switching power supplies are similar, in concept, to the power supplies
that
> were used in car radios prior to the transistor. They used a vibrating
reed
> (designed to vibrate at 60Hz) to switch the 6V (prior to ~1955 most cars
> used 6V) DC voltage on/off, generating a square wave that was fed to a
> step-up transformer to create 120V/60Hz. A standard power supply circuit
> then converted this into the high DC voltages needed by the vacuum tubes
> used in the radio. (Many baby boomers exist because of vibrators and back
> seats.)

That was back before alcohol was known to have serious fetal effects.  I am
sure combining all three elements led to the baby boom!  :=)

> Switching power supplies have replaced the vibrator with electronic
> switching operating at much higher frequencies (20kHz-1MHz, no
> standardization). The higher frequencies mean any transformer and other
> components can be much smaller. They can be highly efficient (but many are
> not) in terms of energy use and they can use a wide range of input
voltages
> so one PS can be used worldwide. Linear power supplies use heavy
> transformers and are inefficient energy users.

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

> 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.

> 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.

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.

> The noise you saw from a CFL using the ESM1 is probably ~120kHz from its
> switching power supply. Since it's a square wave, it contains a lot of
> harmonics so it may be a harmonic of the fundamental switching frequency.

<stuff snipped>

> John Galvin indicated that the Monterey responded to out-of-band noise
that
> did not affect the ESM1 (again, my ESM1 on loan) but he didn't provide any
> further details on frequency/amplitude.

Opps.  Gavin's the actor from Pyscho who became Amb. to Mexico,  Galvin's
the X-10 man.  Erica Gavin was the actress with who starred in Russ Meyer's
classic "Vixen" and had a 38" DD bustline in an age long before silicone
when 38" MEANT something!

> 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.

> For further reading:
>
http://www.electronics-tutorials.com/basics/switched-mode-power-supplies.htm
> http://en.wikipedia.org/wiki/Switch-mode_power_supply
>
http://www.consumerreports.org/main/content/display_report.jsp?WebLogicSessi
on=QskjsPdgjUnIkrGTKBQs1gH2ur22N7aX2ctPO7Qj4mw9i3w3U8z2|8882122804884371552/
169937909/6/7005/7005/7002/7002/7005/-1|5298542958250215617/169937910/6/7005
/7005/7002/7002/7005/-1&FOLDER%3C%3Efolder_id=538847&ASSORTMENT%3C%3East_id=
333133&bmUID=1120478128741

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.

> 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 . . .)

> If a PS causes problems only when it is on, it's most likely a noise
> problem. If it still causes problems when off, it's most likely a
capacitor
> across the mains.

Must of today's PC's are never really "OFF" anymore unless you yank their
cables.

> However, there may be cases where the capacitor is behind
> a switch so that complicates the analysis.

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?

> 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.

> 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.

> 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.

--
Bobby G.