To Jim's remarks I only wish to add this about power supplies and battery
chargers:
Although not an iron-clad guarantee (because there will be exceptions), if
the nameplate or "regulatory" info on a power supply or charger indicates
wide range AC input capability (typically 90 to 250 VAC), then the device
is almost surely a switcher (a.k.a. "noise maker"). A device with a
voltage selector switch (typically "120V" and "240V") could be either a
switcher or linear. With the push for "green" devices and the "EnergyStar"
program here in the USA, virtually all consumer devices with power supplies
use switchers because of their greater efficiency over a linear that
employs series output regulators.
Another clue is size and weight. Iron and copper, as used in the
transformers of linear power supplies, are bulky and heavy, as are the heat
sinks for the voltage regulating transistors. So, if a gizmo's power wart
weighs a few ounces and delivers something like 12VDC at a few amps, it is
a switcher. If the power supply is large and weighs enough to be
considered a dangerous weapon if thrown at someone, then it might be a
linear. If in doubt, open it up and look inside.
A final note about a ham radio product: I purchased an Icom IC-91AD HT
about 2 weeks ago and enjoy it very much. (It is a "true" dual band HT in
that you can display and monitor 2m and 70cm simultaneously.) The included
lithium ion battery pack is charged using the supplied Icom BC-167SA
charger, which is very compact, rated to deliver 12VDC @ 0.5A, and weighs
all of 3.5 ounces!!! As I went thru the paperwork that came with the
radio, I found a sheet labeled "Modification to the supplied AC adapter".
>From the drawings used on the sheet, the "old" BC-167A charger appears to
have been rectangular in shape and had no ferrite clamp-on filter applied
to the DC output cable. (The BC167xx charger is a "wall wart" style that
plugs directly into the wall socket, so the cord from the unit carries only
low voltage DC and has a connector to match the DC input socket on the
radio.) The "new" BC-167SA, as supplied with my radio, appears to be much
smaller and does have a clamp-on style ferrite filter installed about 2
inches from the radio connector end of the cable.
My take on this is that Icom either changed supplier of their power supply
and/or they changed from a linear type to a switcher. If anyone out there
has the older BC-167A supply, please contact me off-list and tell me if it
is a switcher or a linear. The BC-167SA did a nice job of raising the
noise floor in the AM broadcast band when I was listening to Chicago's
WBBM-AM on 780 kHz (I'm in Iowa) and I plugged the charger into the wall
outlet to charge the HT's battery. The AM radio is battery-powered, so the
noise was coming off the DC output cable of the charger. That leaves
little doubt as to why there is that big chunk of ferrite on the cord.
73, Dale
WA9ENA
> [Original Message]
> From: Jim Brown <jim@audiosystemsgroup.com>
> To: <rfi@contesting.com>
> Date: 4/13/2012 3:10:26
> Subject: Re: [RFI] Mystery cyclic buzzing
>
> On 4/13/2012 11:27 AM, Scott Yost wrote:
> > I think we need to do exactly this, and thus build a knowledge base of
RFI sources to help narrow down our searches.
>
> The "exactly this" that we all need to do is carefully poke around our
> homes looking for noise sources. Virtually ALL equipment should be
> considered a POSSIBLE noise source if it has a power supply, a
> microprocessor, a digital clock, even an analog oscillator. BATTERY
> CHARGERS and WALL WARTS of all types are notorious sources of noise.
> This isn't news unless you've ignored RFI for the last 10 years.
>
> We don't need a catalog of "ths sounds like this" as much as we need an
> awareness of the ubiquity of these noise sources.
>
> 73, Jim K9YC
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