Re: Preventing Random X-10 Code interference...

[nobody@xxxxxxxxxxxx (Dave Houston)]

"Robert Green" <ROBERT_GREEN1963@xxxxxxxxx> wrote:

>I got the ACTs for a space heater that uses IR to control it that causes
>X-10 voltage drop and to filter an HP5 laserjet.  They've worked pretty well
>to control X-10 sucker problems but I don't believe they behave well with
>noise problems.  I have a set of felonious CF bulbs that generate enough
>noise for even my ELK meter to see.  As soon as I figure out how to use the
>noise analysis mode of the meter, I can evaluate both filters for noise
>rejection from a device like a compact fluorescent.

The filters are designed for 120kHz so they should be most efficient at that
frequency. All should be better at controlling signal suckers since, in this
case, they need to block 120kHz from reaching the signal sucker. They may be
less efficient at blocking noise since the noise may not be 120kHz but may
still cause trouble for X-10 receivers.

In this particular case, the monitors may be putting noise on the line
directly (from their power supplies) or indirectly via RFI.

Most, if not all, X-10 _brand_ PLC receivers (i.e. switches, lamp and
appliance modules) count the number of cycles in the "acceptance window"
between ZC+250µS and ZC+900µS. Noise that is greater than ~80kHz can cause a
receiver to think it's seeing X-10 carrier while noise lower than ~80kHz
might mask the carrier. So far, nobody has determined the upper/lower
frequency/amplitude limits although Dan Lanciani has documented a case where
a weak +200kHz was jamming X-10 signals.

The problem gets more complicated now that other manufacturers are making
devices that use the X-10 PLC protocol but may or may not use cycle counting
to determine carrier presence/absence. There are schematics available for
many X-10 made devices but not for those made by SmartHome, Leviton, ACT and
others.

Some X-10 made devices are vulnerable to spikes and brownouts which can
result in unwanted on/off events but will not cause valid X-10 PLC signals
that will be sensed/recorded by PLC interfaces.

BTW, most X-10 made PLC interfaces like the TW523, CM11A, CM15A, etc. do not
use cycle counting but sample the demodulated data envelope. They might not
react exactly the same as those that count cycles.

When there are valid X-10 PLC signals on the powerline, the source must be
something that's capable of sending X-10 PLC signals - they are not going to
be created out of whole cloth by a noise source. A likely source is the
SmartHome two-way switches and modules but your guess is as good as mine as
to the exact mechanism whereby "noise" triggers them to transmit.

Receiver sensitivity is another factor. Older X-10 devices needed ~100mVpp
but newer devices and those made by others may respond to much lower signal
(or noise) levels.