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Re: [RFI] Ceiling Fan question

To: Gary@doctorgary.net
Subject: Re: [RFI] Ceiling Fan question
From: dgsvetan@rockwellcollins.com
Date: Fri, 26 Oct 2007 11:03:05 -0500
List-post: <mailto:rfi@contesting.com>

>From everything that the writer, Skip, says, about the only events that 
make at least partial sense are transients of some type and maybe some 
sort of signal from that mountain top RF installation he mentions.  Let's 
consider possibilities.

It certainly is interesting that only one fan at a time is affected, even 
though both are in the same room.  I'll assume that both are also on the 
same AC branch circuit for power.  So, one would think that anything that 
is a transient on the power line would or should affect both fans equally. 
 Since Skip makes it clear that his house is in a very rural location, I 
can relate personally to power line issues in that environment.  My power 
line noise at my QTH goes from no issue at all, even on 160m, to S-9 plus 
all the way up to 6m.  One thing that helps is that in many rural power 
distribution setups, each residence has its own pole pig because houses 
are far apart.  That ceratinly helps to reduce the chances of "junk" from 
one house affecting others.  Notable exceptions might be an arc welder or 
large "universal" types of motors.  Bottom line:  I have doubts that power 
line transients are the culprits.

Let's look at RF.  Skip mentions a possible weather radar on that 
mountain.  If that is the case, he is probably right about it not being in 
the 350 MHz band.  But, does he REALLY know for certain what that radar is 
and its use?  I have two main thoughts about that RF site on the nearby 

1) Five miles is not much of a haul if the offending system is, in fact, a 
high power radar.  I used to live around 5 miles from a Nike-Ajax missile 
site in the Chicago area back in the days of the Cold War.  I could 
usually tell when the Army had their search radar running because it got 
into my stereo system just fine, emitting a nice loud buzz every time the 
dish swept across my part of town. (The phono preamp, with its 47k ohm 
input impedance, was the prime detector of radar pulses.)  The radar does 
not need to be in the same RF frequency band as the fan remote control 
system.  If the signal is strong enough, one or more semiconductor 
junctions can become RF detectors and cause something to happen within the 
fan units.

2) A few years ago, it was widely reported in the media about a whole 
bunch of garage door openers that were triggered in the San Diego area 
when the fleet came into port.  As many of the persons on this list know, 
the band of 225 to 400 MHz is for military use, and the fleet apparently 
had some real strong emitters that were near or on the garage door opener 
freqs in the 300 MHz area.  So, my second thought is that there might be 
some emitter on that mountain that supports military operations and which 
could be operating at or near the remote control frequency of the fans, or 
perhaps there have been nearby fly-overs by military aircraft using that 
frequency range.

I realize that the above guesses do not account for one fan at a time 
being activated.  That very reason is why I think the offender is an RF 
source, rather than a power line transient.  Since we are talking about 
frequencies in the UHF and/or microwave range here, there will be a lot of 
random reflections within the room where the fans are located, as well as 
from objects outside the hosue.  Unless the house has aluminum siding, 
most frame houses are rather transparent to RF, the only other RF shield 
being the aluminum foil applied to the back side of sheet rock as a 
moisture and fire barrier.  So, random reflections could result in one fan 
"seeing" enough signal to trigger at one time, and the other fan being the 
victim next time.  As for the reaction of max speed versus min speed, I 
suspect that is mainly the result of an incomplete "command" that can not 
be properly discerned by the controller. 

I do have doubts that any buried Indians just happen to have a fan remote 
control in the grave with them.  Hi!

73, Dale


"Gary Smith" <Gary@doctorgary.net> 
Sent by: rfi-bounces@contesting.com
10/25/2007 11:24 PM
Please respond to


[RFI] Ceiling Fan question

I just read this request for help on a guitar list I belong to. I 
don't have a great answer for him so I'm posting it here and maybe 
someone has a helpful suggestion.



----- question follows------------

Here's the situation:  Leslie and I just completed an addition to our
home.  It includes two Hunter ceiling fans that are independently
controlled by two remotes.  The remotes are RF, not infrared, and 
at 350MHz.

On Monday, we're sitting in our new room with these fans when the 
fan clicks on and starts rotating at the highest of 3 speeds.  All by
itself!  We can see the remotes across the room.  Nothing touched em, 
and girls.

Yesterday, we're sitting in the same room when it happens again, only 
time it's the south fan at the slowest speed.

We live in an very low RF environment beyond the boonies in rural 
Carolina.  My cell phone doesn't even work here.  No household 
were running; there is very little traffic near us so it's unlikely 
from 2-way radio splatter;  no garage door openers nearby because are
neighbors are not near;  I'm stumped.

There is a mountain peak about five miles away that does have RF 
stuff on
it, possibly including weather radar.  But none of this is 350MHz to 
knowledge.  And five miles is a haul.

No one ever mentioned if our addition is built on an old Indian 
or anything like that.  But, hey, anything could be possible. 
this close to Halloween.  Woooooo!

It's not a big problem but "I gots to know."  Any suggestion on what 
be starting up these fans is appreciated.

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