Here is my newest Kirt's Cogitation. Your
comments are encouraged.
AM/FM Under Siege
The electromagnetic world sure is a noisy place and it is
getting worse all the time - in every region of the spectrum.
Intentional radiation is not so much of a problem because it
usually falls within well-defined limits and is predictable, but
sloppy engineering and, honestly, ignorance, has made life
harder for just about everyone. Listeners to broadcast radio in
both the AM and FM bands have really taken a hit.
has always been prone to interference by its very nature, so
anyone listening expects the occasional pop or hiss from
atmospheric phenomena or a light switch being flipped on or off.
Have someone in the house run a blender or drill and you can
forget hearing anything until the task is completed. It comes
with the territory, so to speak. FM was and is largely immune to
most forms of interference, but lately I have been noticing it
coming from some of the most unusual places.
long as I can remember, I have preferred to have a radio on in
the background whilst whiling away at work and at play. In the
days before Al Gore invented the Internet and Mr. Jobs created
the iPod, my favorite entertainment was provided in the form of
a radio. It was almost always possible to locate at least one
station that played acceptable music, news, or talk shows. Some
otherwise intolerably long days at work were made better by the
presence of radio's subtle diversion. Pulling in broadcast in
both bands from halfway across the country in the nighttime
hours with just a cheap clock radio was really great. I
especially appreciated being able to listen to local news and
weather from, say, Milwaukee, Wisconsin, while tuning in from
Annapolis, Maryland. Keeping current on local happenings is also
one of the primary reasons for my liking over-the-air
Most of us over forty probably have
stories about the lengths we have gone to to pick up radio
stations from within a steel and concrete office building.
Often, it was a team effort. BTW, I now do most of my radio
listening via the Internet because it is hassle-free.
five years ago while living in North Carolina, I tuned into an
AM station during my drive to and from work specifically to hear
local news and weather. The broadcast crew were a couple of real
wits, so the entertainment factor was enhanced considerably by
their presentation. After a couple years of the same route at
the same time every day, I began noticing interference as I
approached a particular area. It would build to a crescendo at
one point, then die out again. It did not happen all the time,
so I searched for a pattern. The common factor was high
humidity, or rainfall. Ah-ha.
I contacted the FCC to
see whether they had gotten any other complaints about
interference. No, they had not. Besides, as I found out, the FCC
no longer (at least at the time) was in the business of hunting
down electromagnetic interference in broadcast radio bands. I
was on my own, per the representative that I spoke with. So, I
called the power company to suggest that the noise might be
originating from a malfunctioning piece of their equipment. I
used my most authoritative electrical engineer voice to explain
how there is a chance I had stumbled upon a disaster waiting to
happen. They bought it.
A week later a field agent
whose job it was to investigate just those types of failures
called back to say he had indeed found a leaky transformer. It
was located back in the woods and serviced a private garage, a
couple hundred feet off the road. He went out on a rainy day
based on my story and said the beast was actually throwing off
sparks. When he talked to the owner about replacing the
transformer, he told the agent something like, "Oh, it's been
doing that for a long time." Ignorance is not necessarily bliss.
Those types of interference can be excused, because they
are not anyone's "fault." The transformer was replaced, and the
noise went away. Some interference should never happen, though,
as with the next couple anecdotal instances.
my YouTube video demonstrating how a pendulum-driven clockworks
operates. Melanie is doing the Vanna White thing.As some of you
may know, I like pendulum-driven clocks. My fascination is
primarily with the mechanical movements, although I have always
appreciated the fine woodworking in many clock cases. Nice
clocks with high quality movements are expensive, so the two
regulator models I own were purchased for a little under $100 on
eBay as near-disasters. I successfully restored both two wooden
cases, and one clockworks, but the mechanical movement in one of
them was too worn out to be repaired easily. The holes in the
metal frame where the gear axles rest were about 50% larger than
the axle diameters. Well-designed clock movements require a
minimum amount of energy input during each cycle of the pendulum
or the balance wheel/spring. When the gears do not move easily,
the main drive spring or weights cannot overcome frictional
forces and the clock either does not run at all, or is does not
run for long with reach rewinding or weight resetting. A video
that I made of the movement that was restorable is now on
YouTube (shown to the right).
Keep reading, please.
There is an RF-related story here.
So, while I wait
until I can stand to part with $300-$400 for a replacement
pendulum movement, I installed an electronic model instead. It
uses a cone speaker driven by a digitized chime sound. The sound
is actually pretty good as it rings out the Westminster tones,
and then a bim-bam for each hour. When listening nearby it
sounds almost like the real thing, but not so back in the
Being electronically generated, the tones
generated by the circuit are not as pure as a solid or tubular
mechanical chime would be. The sound is actually comprised of
the fundamental and harmonics; to what degree I do not know.
However, that fact that they are not pure is made evident by the
way the tones are perceived when in a bedroom or in the kitchen
where the pressure fronts experience the same kinds of multipath
excursions as RF do between the transmitter and receiver.
Various frequency components arrive at different phases that
combine to create some pretty sever distortions. Depending on
where I happen to be in the room, each of the tones can sound
very strange - often enough to make me cringe. Moving to another
spot results in some unique sounds.
A pure tone
would also experience multipath effects, but the perception at
any point would be only a increase or decrease of volume
depending on the overall amount of constructive or destructive
interference, but the frequency is not changed.
here is the RF application that I mentioned. While the
electronic chime is chiming, I get a very high level of noise on
the FM radio (yes, FM) in the 88-90 MHz realm. Evidently, the
clock oscillator that runs the microprocessor for the chimes has
very high harmonics that extend into the FM band (and likely
beyond). The interference is constant throughout the chiming
sequence. My guess is that the movement is violating FCC
regulations for unintentional radiation, but I will not bother
to report them to the Feds - they probably do not care. If the
RF Cafe laboratory had a spectrum analyzer to capture the entire
spectrum, maybe the FCC would take an interest. There is no
visible FCC or CE mark on the case. This is an example of sloppy
engineering causing grief.
I wrote a while back about the
compact fluorescent light (CLF) bulbs that I have deployed
throughout my house, primarily as an energy saving measure. The
slight delay in turn-on time and the color oddity does not
bother me as much as it did initially. It is nice in the summer
to turn on a couple 100 W bulbs that really only add 26 W of
heat to each to the room; that is 74 W of heat that the AC
system does not have to remove to keep me comfy. I have noticed
no RFI issues at all with any of them. Oddly enough, the only
fluorescent light that generated interference has come from the
4-foot high energy (and supposedly high-efficiency) tubes in my
kitchen ceiling fixture. Those things have been around for
decades, and they still mess with AM radios?
Last June (2008), I had a new gas-fired
furnace installed. It is a top-of-the-line, 94% efficient model
from Trane (Model #4TXCB025BC3HCAA). The unit is small because
our house is only 940 square feet. There is a compressor outside
for air conditioning, but it is not configured for double duty
as a heat pump because, I am told, they do not do that up north.
Since, as mentioned earlier, I like to listen to over-the-air
broadcasts when possible, I usually tune in one of the local AM
radio stations. The furnace never ran over the summer so I never
detected any issue with interference. It was not until around
the end of September that when the furnace fired up, it created
a lot of noise on the AM radio - across the entire 520 to 1,610
kHz band. It only occurred with a radio powered off the
household AC supply, not when operated on batteries, so I
deduced that the interference was being conducted through the
household AC wiring, not being broadcast through the air. I was
utterly amazed that a modern system would emit such a high level
of conducted emissions.
Suspecting a potentially
flawed unit, I called the Trane installer. He response indicated
that the gas-fired models do that because of noise generated on
the flame controller board. Fortunately, he is a good guy and
sent a technician out to install an EMI filter on the AC lines
where they exit the controller housing, free of charge. It was a
significant filter, consisting of an isolation transformer, a
couple big coils wound on ferrite toroids, and a couple
capacitors. It completely fixed the problem.
contacted Trane about the interference issue, their terse
response was that I can contact my installer and have a filter
installed for a relatively low price. Being downright indignant
at the slacker attitude, I felt compelled to rip them good in a
letter to the QA department. I quoted conformance requirements
provided to me by me friend and RFI/EMI/EMC expert David Guzman,
of RfTek, and further chided the company for having the
unmitigated gall to install such offensive products in
residential structures. After all, I told them, I have in the
last four years had two competitor HVAC installations completed
in other houses and none of them exhibited any interference at
That must have really put the fear in them, by
Jove. It has been several months now, and nobody at Trane has
dared to contact me in response. Or, maybe they just had a good
laugh around the Continuous Improvement Committee meeting table
at yet another foolish customer who actually expects a quality
product from them.