At 12:39 AM 2002-11-04 , WB2JUF wrote:
>I think I?ve determined that its coming from my home alarm system.
>How do I tackle this? I?ve had the alarm co. here and they insist it?s not
>the alarm system. I?m pretty sure it is.
A few years ago I had the same problem. But through trial and error I found a
technician at the security system office (it was ADT in Syracuse) who told me
the process to follow, and which wires to remove from the control unit, to:
a.) remove the battery backup power from the digital board;
b.) remove all the remote sensor wires from the digital board.
When doing this, I needed to notify them, because those disconnects cause an
alarm in the central office (obviously). They were actually quite cooperative
about it. In fact, rather than mess around trying to "quiet" their circuit
board, I reached agreement with them that on major contest weekends when I
needed really quiet low-band DXing conditions, I could call them and notify
them that I was going to be "out of service" for 24 or 48 or ?? hours.
It should be no surprise that the security system creates RFI -- it has a
digital control board connected to remote sensors through very, very long runs
of plain old unshielded twisted pair wires that tend to be routed all sorts of
crazy ways through your house, often running very near your AC wiring.
In general, there are at least two common sources of RFI in your own home that
can continue to cause problems even when the AC mains are off or disconnected.
As you have discovered, the home alarm system is one. But any UPS
(uninterruptable power supply) is also a candidate -- at least until its
internal battery runs out of gas.
As an aside, it is important to buy a UPS designated for home environments, as
I found out the expensive way. My first TrippLite turns out to have been
spec'd for commercial/office usage, and it puts out a broadband buzz from 1.5
MHz to 3.6 MHz. My latest TrippLite seems to be clean; it's spec'd for home
use. (FCC Type A versus Type B, but I don't remember which is which.)
By the way, a few years ago I tracked down an unexpected source of low-band RFI
that I had unwittingly brought into my own house -- a Canon multi-function
fax/copier/scanner !!! (It created the noise even when it was just sitting
idle, waiting for incoming faxes.) Of course, the problem went away when the
power went out, but so did most of my low-band DXing....
One other source of noise that took me a while to figure out: most newer
garage door openers have an "electric eye" circuit that senses for obstacles
(little children, especially) about a foot above the garage floor and stops or
reverses the downward motion of the door if such an obstacle is detected. On
my 3-year old openers, whenever the garage door is open (not just in motion,
but open and not moving), the circuitry throws major hash into the AM broadcast
band and of course 160. Again, the wiring to the remote sensors is unshielded
twisted pair.
Bud, K2KIR
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