Re: X-10 RF Freq Mod

[nobody@xxxxxxxxxxxx (Dave Houston)]

Just Another Joe <address@xxxxxxx> wrote:

>Hi Dave,
>
>For some reason, I've just seen your replies today, even though sent two
>days ago.

It's those postal inspectors in your country. ;-)

>On Wed, 20 Dec 2006 00:51:10 GMT, nobody@xxxxxxxxxxxx (Dave Houston)
>wrote in message <45888396.382829218@xxxxxxxxxxxxx>:
>
>> Just Another Joe <address@xxxxxxx> wrote:
>>
>> >My question is, can X-10 transmitters such as palmpads, slim-switches
>> >and motion-detectors, be [easily] tuned to 315MHz?  If so, one could
>> >have, for example, motion-sensors on 315MHz and controllers on 310MHz,
>> >to prevent one from stomping on the other.  Is that feasible?
>>
>> No. X-10 transmitters are not easily tuned - most can only be tuned by
>> bending the wire loop that forms part of the resonant circuit and you need
>> sophisticated equipment to do this accurately...
>>
>> 315MHz and 310MHz are also close enough that strong signals will be received
>> from either frequency by the superregenerative receivers typically used. You
>> need more separation.
>
>Yes.  In later reading through some X-10 forums, I saw mention of the
>x10.com transmitters being /very/ loose in frequency, so I suspected
>310MHz and 315MHz would be too close.

That's mostly urban legend propagated by the "X-10 is the spawn of Satan"
crowd. In fact, I find they are remarkably accurate given that they use LC
components (and crude tuning methods during manufacturing) instead of SAW or
XTAL to control the frequency.

I do not have laboratory type of equipment to measure frequencies from ultra
low power transmitters but I do have SAW controlled 310MHz transmitters. If
I tune one of the RF receiver modules to the SAW transmitter, the receiver
tends to work equally well with the LC tuned X-10 transmitters (using its
linear output as an RSSI indicator).

>> However, RF interference from multiple transmitters is not much of a
>> practical problem. PLC interference when various receivers try to send to
>> the powerline simulaneously is the "usual suspect".
>
>This is interesting.  As you know, I'm planning on switching to Insteon,
>but hope to keep the X-10 RF (and plug-in) transmitters for control at
>least until suitable Insteon versions are available.  And, to interface
>them to the Ocelot via roZetta, rather than via RR501's as they
>currently are.
>
>But I recently dusted off some X-10 motion sensors to try again, and
>found that I was frequently getting collisions when sending palmpad
>commands.  So from what you said above, would you suspect that the
>collisions were occurring on the PLC side, rather than the RF side?  If
>so, then without the PLC in the picture, perhaps palmpads and motion
>sensors can co-exist peacefully?

It's really hard to speculate without knowing details. How are you
determining that there are collisions? It's been a long time since I looked
at this in detail but the motion sensors will not respond to further motion
for some period of time after transmitting. The RR501 will detect PLC
collisions, back off and retransmit once the powerline is clear. The RR501
can also buffer one command. All this makes collisions improbable.

RF collisions will not result in a anything on the powerline as the RR501
only transmits to the powerline after validating the received RF is a valid
X-10 command. There's no simple way aside from a 'scope watching the linear
output of a receiver to detect RF collisions.

My earlier comments reflected the prevalence of newbies putting multiple
motion sensors where they can detect the same motion with only a brief
interval or no interval and using TM751 transceivers which do not buffer any
commands and cannot avoid PLC collisions since they cannot detect PLC
activity.


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