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March 5th 05, 08:35 PM

From: on Fri, Mar 4 2005 10:18 pm:

I've done the google search already, so I hope maybe one of you has an
answer.

I am in the beginning stages of setting up my station, and I am
getting
lots of EMI from various applicances in the apartment. I used an SW
pocket radio as a sniffer.

Good procedure.

It turns out that most of these are throwing out hash back into the AC
line,
and that the AC wall conduits are conducting EMI into the room my wife
allows me to use for my station. My station is on the other side of
the apartment, but it doesn't matter about the physical distance
because the
AC lines are throwing off the worst of the noise. I turned off
EVERYTHING
and was able to reduce the problem enough to hear CW on the 7.050 on
my
pocket radio without an external antenna.

Throw everything on, and I could barely hear the signal with antenna,
because EVERYTHING is going back into the house wiring!!!

Chances are that your apartment structure is not using metal
conduit for the AC lines. That helps quite a bit but is NOT an
option for a renter. :-(

From worst offenders to least worst, they a

1) GE Hotpoint refrigerator/freezer.
2) Air conditioning system.
3) Aquarium pump.
4) Overhead florescent lights.
5) Microwave oven (even in in standby mode!).
6) LED alarm clocks (3)
7) Telephone answering machine
8) Cordless telephone base station (900 Mhz)
9) Cable Modem
10) Wireless Router
11) Late model Computer and CRT Monitor.

Typical household using modern appliances...all with little
electronic
circuits in them generating wideband RF hash. Very good for
reducing the "standby" load to the power company (energy
efficient if they have "power factor correction" circuits) but a
total
#$%!!! for anyone wanting to receive MF to HF signals near them.

I have the following assets:

1) I live on the lower floor and have a water pipe just outside the
window
of my station room.

I doubt whether that will help in any real way, except for possible
lightning strike re-direction. Leads to the (grounded, supposedly)
water pipe are inductive and little antennas by themselves.

2) I just bought 4 each of 3 amp and 30 amp CORCOM line filters on
Ebay.

Seriously, anyone saying "those always work" are probably selling
line
filters. It's a case of trying them out to find out if they do in
that case.

3) A bunch of FT-50-43 cores.

Better than nothing.

4) My wife's loving patience.

PRICELESS! Keep that at the expense of everything else!

Questions:

1) Ferrite 43 material is supposed to attentuate for 20 Mhz and up,
and the
frequencies I want to hear are at 80 thru 20 meters. Should I
use the 73
material instead for wrapping AC cords around toroids for
common-mode
chokes?

Probably, but I suggest trying the 43 first. ANY attenuation at the
offending appliance is better than none. Do it as close to the
appliance as possible, lessen the RF hash dribbling out the lines.

2) Do modern refrigerators in apartments use ordinary AC sockets or
3-phase?

Both. Depends on model and size. Wife and I had a TOTAL makeover
of our kitchen and laundry alcove in 1999, outlets were on the list
to
check for all new appliances in case of rework of residence wiring
was
needed. We now have an un-fancy fridge/freezer with "old" control
system, minimum of EMI-generating circuitry within, no bells or
whistles. Most residential refrigerators seem to use 115 VAC single
phase with conventional 3-prong connectors. I say "seem to" based
on
a three-inch thick notebook of kitchen appliance data researched 5
1/2 years ago.

The front-loading washer and dryer in the laundry alcove had the
ordinary synchronous motor driven timers/cyclers, no bells and
whistles with little electronic clocks or other dinguses added on
(big sales feature in the stores, like seeing digital time is a
big plus).

3) I have a 1500 watt microwave oven, can I have it also run off a
CORCOM
filter?

The 30 A version; 1.5 KW will draw about 14 A through the line.
A problem there is that the line filter should be grounded to
something close to ground (like the old Los Angeles electrical
code which mandated metal conduit everywhere). The case of the
microwave is metal and it has lots of shielding for 2 GHz RF.

On the other hand, it may be just the clock/timer/controller that is
generating EMI and that is rather low power. All of those use a
microcontoller for all those selectable settings and probably have
their own internal DC supply in parallel with the heavy-duty
magnetron supply. All bets are off if there's a "power factor
corrector" circuit in that supply for the maggie...those are
modified switchers and may or may not be EMI generators.

3) Can I use a CORCOM filter to isolate EMI from each appliance (30
AMP)
and from the aquarium pump (3 AMP) from the AC lines? Or, do I
also
need common-mode chokes?

Again, it's a matter of where to connect the ground/common of the
line filter. Filter ground to metal conduit ground works fairly
well but
unknown on Romex wiring or PVC conduit electrical line routing.
One has to experiment there.

4) I split the wall wires of the wall wart and would each polarity
around
its own FT-50-54 about 4 times. Will this be remotely as
effective as
winding the wall-wart cord around a larger toroid?

Probably, but that's again a matter of experiment. Ain't NO
absolutes
when there's all those other environment unknowns.

Ferrite or iron powder material, any kind, will REDUCE the EMI but
none of them can eliminate it completely. Commercial equipment that
must meet government radiation specs will use the least amount
necessary to save costs and they rarely publish data on the amount
of
reduction. All have to experiment with it. For what it's worth, a
large toroid can be an advantage in stringing the wall-wart lead-out
through it, forming a large common-mode choke. It also costs more.
shrug

=======

From my own experience in a metal-conduit-AC-line house built in
1962, the worst EMI offenders are the "efficiency" light bulbs which

have switchers of some sort inside their bases. Some brands are
low EMI (sold under the GE label), others are high EMI (sold under
Philips label). It's a "caveat emptor" thing. :-(

I've done the portable all-band receiver sniffing here (borrowed
wide-
band scanner type) and found few real offenders at several feet from
their locations. Offhand, I'd say that metal conduit AC
distribution
is a real help in reducing EMI. Appliances that include
microcontroller devices in all the clocks but one, a bells-and
-whistles Amana microwave, a Braun coffee maker (replacing a
venerable Mr. Coffee), digital light timers, TV cable set-top box,
VCR, cordless phone, combo FAX and phone recorder, electronic
thermostat for furnace/air system, radio-alarm in bedroom. All of
those do produce some EMI but the sniffer has to be right on top of
it for detection. The gas furnace has an electronic ignition which
makes an obvious spark, as do the range-top burners in the kitchen;
never thought to sniff for those but I've not heard any obvious EMI
from those.

An ancient-but-still-in-spec Icom R-70 sits on the arm of a desk in
the office room with a fluorescent light bar (two 40 W tubes in an
L, home-built) right above it. When the outside long-wire blew down
I tried the 8-foot aluminum window frame above it as an indoor
antenna and got incredible EMI hash. Fluorescent lights in the
kitchen (two) and in the attached garage (also two) are very minor
sources of EMI here. When connected to the outside long wire
there was no problem light on or off. That includes the kitchen
fluorescents, close to the outside coax connection to the long-wire.

Replacing my computer's CRT monitor with an LCD flat monitor
helped reduce EMI spritz from my computer. My wife saw the nice
thing I got (special sale at Fry's), she wanted one for her computer
too! :-) That dropped the internal EMI level (R-70 hasn't been
connected to an outside antenna yet) some more. Both computer
boxes are nicely-shielded-case HP Pavilions with internal modems
and such...not like the el cheapo PC box obtained in 1998. There
are some EMI bursts from the external flat-bed scanner and the
inkjet printers but neither scanning nor printing is done at the
same
time as receiving HF RF (scanner has its own outside antenna).
Battery-powered radio clocks don't seem to radiate much of
anything except the correct time. :-)

Using a conductive chassis/enclosure and incorporating any kind of
line filter in a piece of equipment will help reduce EMI both coming
and going. The line filter common is made right to the chassis/
enclosure and that is the best connection. If the residence has
Romex or equivalent wiring, chances are that an HF transmitter will
be the major EMI cause for OTHERS, especially in an apartment
building. That's worse if the Rx/Tx antenna is IN the apartment.

An outside antenna (if possible) will reduce EMI garbage input to
any receiver, any user's environment.

==========

"Outer space" is only a half-hour's drive away...if your car can go
straight up... :-)

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