Back in July and the first part of August I did some moonlighting at a
lab that certified equipment for
FCC class A or Class B compliance. It was educational and I was
dismayed to see just how bad something can be and still pass.

For SWLs the main aspect of FCC certification is the conducted specs.
Radiation, direct
transmission through the air, becomes more of an issue at higher
frequencies, above 30 MHz.
Below 30 MHz the focus is on conducted emissions. This mainly deals
with signals conducted
via the AC mains. RF can and is conducted into every conductor
connected to a device. And
each conductor must be inspected and measured.

Laplace Industries makes some very good test equipment, and while I am
certain that other companies make equally good or better equipment,
the lab I worked at primarily used Laplace.

The average radio type regardless of focus, by this I mean SWL or ham,
often has no idea what
FCC certification means.

Class A, business, commercial or industrial 0.45KHz~1.6MHz 1000uV,
1.6MHz - 30MHz 3000uV.
Class B, home, residential, is limited to 300uV. for the entire .45KHz
through 30MHz bandwidth.

Expressed another way.
Class A
0.15~0.50MHz 66 dBuV
0.50~30MHz 60 dBuV
Class B
0.15~0.45MHz 56 dBuV at 150KHz decreasing to 46 dBuV at 450KHz
0.45~0.50MHz 46dBuV
0.5~30MHz 50 dBuV

For the official wording from the FCC checkout http://
frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?
TITLE=47&PART=15&SECTION=207&YEAR=2001&TYPE=TEXT

The voltages are measured in a device that,while IMO, is not
representative of the real world, it
does give repeatable readings. A typical test facility will have a
screen room, with a measurement
bench that is 1/8, or more, copper. There are specific requirements as
to how the power leads
from the Equipment Under Test (EUT) are to be routed but we will
ignore them. The AC from the
real world comes in through a LISN. Line Impedance Simulation Network.
A diagram can be found
on page 12 of http://www.ets-lindgren.com/manuals/4810.pdf. The
most important part is the
50uH inductors and the 50 Ohm termination. Trust me, no AC wiring is
anything like a constant
impedance!

"Class B" devices conducting 300uV into your household wiring will
cause significant interference
to the recption of any but the strongest signals!
"Class A" devices which are allowed 1000uV to 3000Uv are nightmares!

About the only way to cope is to never ever use Class A devices, and
many PC network devices
are Class A! Even quieter Class B will almost always require
additional filtering on the AC mains
to reduce the RFI to "acceptable" levels. I have found the Curtis 2
stage RFI/EMI filters offered by
Hosfelt Electronics for less then adollar apeice to be very effective
at managing RFI.

One thing to keep in mind is that medical devices, such as CPAP, BiPAP
and APAP devices used
for sleep apnea are regulated by the FDA and the FCC sets no RF limits
on them. My wife's APAP's
switch mode power supply barely meets Class A requirements. I am lucky
because we went with
an APAP with an external 12V "emergency" power port, so I build a
linear power supply that when
coupled with a Curtis filter is quiete enough that further effort is
not justified.

One of the nicer toys that I got to play with was a PLIP.
http://www.laplaceinstruments.com/PDFiles/plip.pdf

Chuck W1HIS offered some usefull information on my efforts to build my
own. Unless you know
what you are doing, and by this I mean an EE with enough real world
experience to build something
that you will be attaching to the AC mains and to insure your safety,
don't even think of trying to
duplicate the PLIP. I will not give construciton details except to say
that for the average ham/SWL
the 30dB amp is not needed!! If 30dB of amplification is needed, there
isn't a problem.

My home made PLIP has allowed me to study how RFI travels through the
AC wiring, and how it is coupled into other conductors, telephone,
ethernet etc, and it allows me to rapidly see if my RFI reduction
efforts are working.

A 50 uH LISN can be used on DC power lines to check for noise and I
have used it on
our telephone line to verify the presence of incoming noise from DSL
being deployed in our
area. My LISN is a "do all" and has connections that the UL, or local
electrical inspector would
freak if they saw it. I can use it on 120V AC, up to 15A on DC, the
telephone line and anyother
conductor I wish to test. Very flecible but great caution must be
taken to keep from exposing
one's self to lethal voltaages.

As I discribed before a portable receiver that covers trhe frequencies
of interest and an inexpensive
home made sniffing coil of ~20 turns on a plastic pill bottle
connected to the receivers antenna
input can be very useful. Given the risks a PLIP creates, I must
advise that for all but the most
stubborn and possibly fool hearted, the loop is the way to go. With my
home made PLIP and
LISNs I can make measurements that are repaetable and allow me to gain
a better understanding
of the issues in fighting RFI. It is a never ending battle. When you
find one source and remove or
reduce it, another unheard noise source reveals itself. My wife says
I am no longer a SWL but a
RFI fighter. Details for my RFI sniffing loops and the "B-filed" loop
used by Chuck, W1HIS, can be
found at the yahoo groups stopRFI page. I hope to expand this piece
and include a generalised set
of diagrams of that will be safer then my LISN and the mods I made to
allow measurment of
"differential mode" and "common mode" noise.

Reducing DM noise at the source will prevent it from being converted
into to CM noise.

This is the most important leason I have learned.

DM, by itself, is a minor problem.

CM is the real RFI problem.

More data can be found at
http://www.ce-mag.com/99ARG/Gubish31.html.bak.

Terry

"David" wrote in message
...
On Tue, 25 Sep 2007 05:44:51 -0700, wrote:

This is why real DXers drag 12 V marine batteries to the beach.

I have one under my desk.

Burr

Big, Lead, Mean & Clean

On Tue, 25 Sep 2007 05:44:51 -0700, wrote:

This is why real DXers drag 12 V marine batteries to the beach.

I went to Hosfelt Electronics site, couldn't find those Curtis
filters. Can you provide a link?

On Sep 25, 8:44 am, wrote:
Back in July and the first part of August I did some moonlighting at a
lab that certified equipment for
FCC class A or Class B compliance. It was educational and I was
dismayed to see just how bad something can be and still pass.

For SWLs the main aspect of FCC certification is the conducted specs.
Radiation, direct
transmission through the air, becomes more of an issue at higher
frequencies, above 30 MHz.
Below 30 MHz the focus is on conducted emissions. This mainly deals
with signals conducted
via the AC mains. RF can and is conducted into every conductor
connected to a device. And
each conductor must be inspected and measured.

Laplace Industries makes some very good test equipment, and while I am
certain that other companies make equally good or better equipment,
the lab I worked at primarily used Laplace.

The average radio type regardless of focus, by this I mean SWL or ham,
often has no idea what
FCC certification means.

Class A, business, commercial or industrial 0.45KHz~1.6MHz 1000uV,
1.6MHz - 30MHz 3000uV.
Class B, home, residential, is limited to 300uV. for the entire .45KHz
through 30MHz bandwidth.

Expressed another way.
Class A
0.15~0.50MHz 66 dBuV
0.50~30MHz 60 dBuV
Class B
0.15~0.45MHz 56 dBuV at 150KHz decreasing to 46 dBuV at 450KHz
0.45~0.50MHz 46dBuV
0.5~30MHz 50 dBuV

For the official wording from the FCC checkout http://
frwebgate.access.gpo.gov/cgi-bin/get-cfr.cgi?
TITLE=47&PART=15&SECTION=207&YEAR=2001&TYPE=TEXT

The voltages are measured in a device that,while IMO, is not
representative of the real world, it
does give repeatable readings. A typical test facility will have a
screen room, with a measurement
bench that is 1/8, or more, copper. There are specific requirements as
to how the power leads
from the Equipment Under Test (EUT) are to be routed but we will
ignore them. The AC from the
real world comes in through a LISN. Line Impedance Simulation Network.
A diagram can be found
on page 12 of http://www.ets-lindgren.com/manuals/4810.pdf. The
most important part is the
50uH inductors and the 50 Ohm termination. Trust me, no AC wiring is
anything like a constant
impedance!

"Class B" devices conducting 300uV into your household wiring will
cause significant interference
to the recption of any but the strongest signals!
"Class A" devices which are allowed 1000uV to 3000Uv are nightmares!

About the only way to cope is to never ever use Class A devices, and
many PC network devices
are Class A! Even quieter Class B will almost always require
additional filtering on the AC mains
to reduce the RFI to "acceptable" levels. I have found the Curtis 2
stage RFI/EMI filters offered by
Hosfelt Electronics for less then adollar apeice to be very effective
at managing RFI.

One thing to keep in mind is that medical devices, such as CPAP, BiPAP
and APAP devices used
for sleep apnea are regulated by the FDA and the FCC sets no RF limits
on them. My wife's APAP's
switch mode power supply barely meets Class A requirements. I am lucky
because we went with
an APAP with an external 12V "emergency" power port, so I build a
linear power supply that when
coupled with a Curtis filter is quiete enough that further effort is
not justified.

One of the nicer toys that I got to play with was a PLIP.
http://www.laplaceinstruments.com/PDFiles/plip.pdf

Chuck W1HIS offered some usefull information on my efforts to build my
own. Unless you know
what you are doing, and by this I mean an EE with enough real world
experience to build something
that you will be attaching to the AC mains and to insure your safety,
don't even think of trying to
duplicate the PLIP. I will not give construciton details except to say
that for the average ham/SWL
the 30dB amp is not needed!! If 30dB of amplification is needed, there
isn't a problem.

My home made PLIP has allowed me to study how RFI travels through the
AC wiring, and how it is coupled into other conductors, telephone,
ethernet etc, and it allows me to rapidly see if my RFI reduction
efforts are working.

A 50 uH LISN can be used on DC power lines to check for noise and I
have used it on
our telephone line to verify the presence of incoming noise from DSL
being deployed in our
area. My LISN is a "do all" and has connections that the UL, or local
electrical inspector would
freak if they saw it. I can use it on 120V AC, up to 15A on DC, the
telephone line and anyother
conductor I wish to test. Very flecible but great caution must be
taken to keep from exposing
one's self to lethal voltaages.

As I discribed before a portable receiver that covers trhe frequencies
of interest and an inexpensive
home made sniffing coil of ~20 turns on a plastic pill bottle
connected to the receivers antenna
input can be very useful. Given the risks a PLIP creates, I must
advise that for all but the most
stubborn and possibly fool hearted, the loop is the way to go. With my
home made PLIP and
LISNs I can make measurements that are repaetable and allow me to gain
a better understanding
of the issues in fighting RFI. It is a never ending battle. When you
find one source and remove or
reduce it, another unheard noise source reveals itself. My wife says
I am no longer a SWL but a
RFI fighter. Details for my RFI sniffing loops and the "B-filed" loop
used by Chuck, W1HIS, can be
found at the yahoo groups stopRFI page. I hope to expand this piece
and include a generalised set
of diagrams of that will be safer then my LISN and the mods I made to
allow measurment of
"differential mode" and "common mode" noise.

Reducing DM noise at the source will prevent it from being converted
into to CM noise.

This is the most important leason I have learned.

DM, by itself, is a minor problem.

CM is the real RFI problem.

More data can be found at
http://www.ce-mag.com/99ARG/Gubish31.html.bak.

Terry