RFI:
What is RFI?,
What are the sources of RFI?

When I talk about RFI I am referring to "man made" noise, or as hams
call it, QRM. While RF noise does come from many natural sources
such as lightning, the sun, Jupiter and even the cosmos, there isn't
much we do about those other then try to use directional antennas to
minimize the unwanted signals and to maximize the desired signal.

For the most part man made noise, happens whenever an
electric circuit is opened or closed. Either state change will
produce a noise pulse. Frequently opening produces more noise.

For those of us who live in single family houses, most of our noise
is very likely self-inflicted.

RHF has a nice, if over simplified, explanation:
"RHF's circles of noise".

Think of "The Distance Away" from Sources of Noise as
being your Friend. [ Less Noise -and- Stronger Signals ]

# 1 - 10-25 Feet "Away From" The House / Structure.

# 2 - 10-25 Feet "Up Above" The Ground / Surface of the Stucture.

# 3 - Combining both #1 and #2 are even better.

As you move the Antenna Element 'away-from' things
that are the Sources of RFI /EMF the Signal Strength
of the Noise becomes Less by the Square of the Distance

Distance and Signal Strength
1-Foot-Away = 1 Unit of Signal Strength relative to 1-Foot-Away

2-Feet-Away = 1/4th Unit of Signal Strength relative to 1-Foot-Away

3-Feet-Away = 1/9th Unit of Signal Strength relative to 1-Foot-Away

4-Feet-Away = 1/16th Unit of Signal Strength relative to 1-Foot-Away

5-Feet-Away = 1/25th Unit of Signal Strength relative to 1-Foot-Away

10-Feet-Away = 1/100th Unit of Signal Strength relative to 1-Foot-
Away

15-Feet-Away = 1/225th Unit of Signal Strength relative to 1-Foot-
Away

20-Feet-Away = 1/400th Unit of Signal Strength relative to 1-Foot-
Away

25-Feet-Away = 1/625th Unit of Signal Strength relative to 1-Foot-
Away

Now if the Signal Strength of the Broadcast Signals at each
Distance were to remain the same : Then the Relative
Signal-to-Noise Ratio would run-out like this :

1-Foot-Away = Signal-to-Noise Ratio = 1:1

2-Foot-Away = Signal-to-Noise Ratio = 1:1/2 ~ 2:1

3-Foot-Away = Signal-to-Noise Ratio = 1:1/9 ~ 9:1

4-Foot-Away = Signal-to-Noise Ratio = 1:1/16 ~ 16:1

5-Foot-Away = Signal-to-Noise Ratio = 1:1/25 ~ 25:1

10-Foot-Away = Signal-to-Noise Ratio = 1:1/100 ~ 100:1

15-Foot-Away = Signal-to-Noise Ratio = 1:1/225 ~ 225:1

20-Foot-Away = Signal-to-Noise Ratio = 1:1/400 ~ 400:1

25-Foot-Away = Signal-to-Noise Ratio = 1:1/625 ~ 625:1

The Bottom Line : Distance 'away' from Sources of Noise
is your Friend.

BEYOND THIS IS - The Ever Expand Sources-of-Noise
[ Circles-of-Noise in a World Full of Noise ]

1 - Starting with the Primary Point-of-Noise
[ First Circle of Noise ] Remember -It All Begins With You.
= = = Your Very Own House (1X-to-the-X)

2 - Second Circle of Noise
= = = The Houses of your Next-Door-Neighbors (8 X/Distance Away)

3 - Third Circle of Noise
= = = The Houses of your Near-by-Neighbors (64 X/Distance Away)

4 - Fourth Circle of Noise
= = = The Houses within your Neighborhood (512 X/Distance Away)

5 - Fifth Circle of Noise
= = = The Houses and Buildings in your City (16K X/Distance Away)

6 - Sixth Circle of Noise
= = = The Everything in your State (4M X/Distance Away)

7 - Seventh Circle of Noise
= = = The Everything in your Nation (256M X/Distance Away)

8 - Eigth Circle of Noise
= = = The Everything in the World (66B X/Distance Away)

9 - Ninth Circle of Noise
= = = The Everything in the Solar System (4T X/Distance Away)


There are 2 ways a RF noise can reach our receiver. The first is
the device radiates noise directly to the the world where it reaches
our antenna. This is much more common above 30MHz and in general,
even nasty devices, like my wife's never to be cursed enough APAP
(Sleep Apnea) machine, radiate minimal RF noise. The machine's
physical size is too small and the internal wiring is just too short
to
effectively radiate RF below 30MHz

The second, and the method that really creates 99% of our RFI problem
is "conduction", or conducted noise.

This is RF that is injected back on to the power line, or in the case
of a
Modem, on to the telephone line, or any conductor.

This is a problem because, while the device itself may be an
insignificant
radiator, The power line or telephone line are very effective
radiators. I
have left out other conductors and devices like router/hubs and
Ethernet
cable, HiFi audio speaker runs, DBS coax runs, Cable TV coax runs.
But
hopefully you get the idea. A noise source that is coupled to any
conductor
is a potential problem

And any device which bridges or straddles two, or more conductors is
much more likely to be a problem. The two different sets conductors
give
the device a excellent chance to radiate by the "dipole" antenna that
is
created.


For the most part man made noise happens whenever an electric circuit
is
opened or closed. Either state change will produce a noise pulse. In
most
situations, opening or breaking the circuit produces the most noise.

Every time a light is turned on or off, a universal motor's brushes
commutate,
a diode turns off, or a logic gate changes state, a noise pulse is
produced.
Since people don't normally flip lights on and off all the time, these
aren't
much of a problem. However everything else I mentioned is a problem.
The
diode that is used to convert AC into DC turns on and off 60 times a
second.
In many power supplies, two diodes are used to capture both halves of
the AC,
so while each diode may only turn on and off at 60Hz, Togather they
turn on and
off 120 times a second or at 120Hz. (And yes I am leaving 4 diode,
bridge
rectifiers out of the conversation)

Diodes are a very common source of noise. As each diode turns off, or
commutates,
there is a small instance of time where a reverse current can be
thought to flow. It is
more complex, but let us live with simple explanations because the
real situation is
very complex and involves much more math then we need to know then to
just accept
the over simplistic viewpoint and use it to derive a solution. This
narrow noise pulse is
extremely broadbanded. It generates hash from 600Hz to upper VHF,
200MHz at least.

Any device with 'logic' inside is an almost certain noise source.
There are three problem
areas.

1)Power supply noise, typically Switched Mode (SM),
and as noisy as they come.

2)The individual logic gates will produce RF transient
noise pulses with every state change.

3)Most logic system have at least one "clock:, this may be derived
from the AC mains or
more commonly from a crystal or ceramic resonator oscillator.

Noise sources 1 and 2 tend to be broad band.
Source 2 may have strong peaks around multiples,
or sub multiples of the clock(s).

Source(s) 3 will mainly be one strong signal per clock, and harmonics
that easily extend to
above 150MHz.

Here in central Ky a popular ham repeater transmits on 146.76. 3.58MHz
is a very popular
clock frequency. And the 41st harmonic falls about 10KHz above 146.76.
So many devices
that use 3.58MHz as their clock make listening to the 76 machine less
then fun. I have a
digital clock built in the mid 1970s that uses a 3.58 clock divided
down to produce 60Hz.
I have NEVER been able to quieten this project down enough to allow it
to be used in my
radio room! The 3.58 divider is a CMOS device that is unbelievably
noisy.

CFL (compact florescent lamps) are a very popular energy saving device
that many people
are adopting,and many more will adopt given the high price of energy.
CFLs can be very
benign or nasty sources of RFI. The better units are very noisy within
a foot or so, but do
not couple significant RF back on to the AC mains. Cheaper units,
which are all too often
poorly designed, made with inferior parts and produced with little or
no quality control may
be a major RFI source.

One new source of RFI will soon be in large scale distribution. LED
replacements for incandescent
bulbs exist are certain to become popular. And like CFLs they will
come in differing qualities.
Well designed units, assembled with skill from good parts and checked
by a good QC program
will be nearly as quite as a incandescent bulb. But market forces will
produce inferior units. I
am lucky because a friend has a venture startup that is in the test
phase of LED replacement
manufacturing. I have a nice selection of LED replacements that are
very efficient and very quiet.

I also have some early prototypes that were built with IR LEDs that
are horrible noise sources.
No big deal, as the IR units are destined to be used with PIR
controllers to allow us to see in
the dark if some one intrudes in our yard. Cheap CCD cameras are very
sensitive to IR. But
they do show that poor designs will be a major problem!

Water heaters, heating pads, electric blankets and HVAC controllers
can all be sources of very
strong RFI.

Modern Christmas lights and ornaments can be a nightmare. The fancy
lights blink under logic
control and the long strands of wire make effective antennas that can
radiate very strong
signals. Sadly there is nothing that can be done about your neighbors
decorations.

I have left out external power line issues.

I will give some links and leave it at that for the time
being.
A good overview of the issue
http://www.arrl.org/tis/info/powerline-FAQ.html

The following is the best single AC RF noise reference I have found. I
can't wait for the internal
version mentioned in the handbook!
arrl.org/tis/info/HTML/power_line_handbook/ExternalNoiseHandbook.pdf

This is not intended to be a complete list of RFI sources, I doubt if
enough paper exists for
such a list! But it should give readers an idea of noise sources.

Terry

wrote:
RFI:
This is not intended to be a complete list of RFI sources, I doubt if
enough paper exists for
such a list! But it should give readers an idea of noise sources.

Terry

My Dad had an aquarium heater with a neon lamp that destroyed my MW
listening when I was a kid.

Also, the neon lamp in a lighted doorbell button can become a random HF
static generator audible for a hundred feet or more.

Solid state motion detector lamp controllers are also very odious. The
ones from Grainger with a relay are OK.

On Nov 28, 9:39 am, David wrote:
wrote:
RFI:
This is not intended to be a complete list of RFI sources, I doubt if
enough paper exists for
such a list! But it should give readers an idea of noise sources.

Terry

My Dad had an aquarium heater with a neon lamp that destroyed my MW
listening when I was a kid.

Also, the neon lamp in a lighted doorbell button can become a random HF
static generator audible for a hundred feet or more.

Solid state motion detector lamp controllers are also very odious. The
ones from Grainger with a relay are OK.

Like I said, this isn't a complete list. When I build a web page I
will add RFI
sources as they are mentioned. This would be a good place for people
to start
listing any sources I neglected.

Along with aquarium heaters, we have to add "hot rocks" for lizards.
And along with door bell neons, there are many power strips with neons
either in the power switch or a separate power indicator.

I have a list of several hundred and only picked the most common.

A friend had an AC powered ion smoke detector that was an amazing
broadband RFI source!

Terry

On Nov 28, 9:39 am, David wrote:

My Dad had an aquarium heater with a neon lamp that destroyed my MW
listening when I was a kid.

Also, the neon lamp in a lighted doorbell button can become a random HF
static generator audible for a hundred feet or more.

Solid state motion detector lamp controllers are also very odious. The
ones from Grainger with a relay are OK.

I failed to include the latest wrinkle in heat pumps.

The single phase 60Hz is converted to variable frequency

3 phase to drive both the compressor and the blower.

The better units use 2 converters, each optimized for
the motor it is driving.

These are very efficient, but the 11 I have seen have
all had intense RFI that will be very difficult to reduce.

I also neglected to mention exterior "security" lights.
Both Mercury and "low pressure Sodium" lights can be
major RFI offenders. In my experience the photo eclectic
controllers can be nasty RFI sources even when the light
is off.

Terry

Lots of info on RFI at AC6V's site URL:
http://ac6v.com/techref.htm#RFI

Lamont

On Nov 28, 11:22 am, "The Shadow" wrote:
Lots of info on RFI at AC6V's site URL:http://ac6v.com/techref.htm#RFI

Lamont

Thanks for the link, somehow in my hours of wasted net searches I
missed that one.

Terry