Several years ago, maybe a decade ago, I was given three Compaq tower PCs
to support my radio astronomy interests. I couldn't use them for their
tremendous generation and radiation of RF energy! However, I "fixed" one
of them by properly installing a good Corcom line filter right where the
connection to grid power was provided. Someone in marketing (??) decided
not to spend the small amount of $$$ to install either a common mode choke
or the proper line filter. Money talks.
Dave - WÔLEV
On Wed, Sep 25, 2024 at 7:04 PM Jim Brown <jim@audiosystemsgroup.com> wrote:
> On 9/25/2024 8:41 AM, Greg Troxel wrote:
> > A related question is that given a physically small device that plugs
> > in, how are these able to generate common-mode current, given the lack
> > of a counterpoise for an endfed (which is of course not quite endfed,
> > but very off center)?
>
> The antenna, including counterpoise, is all of the wiring to which the
> noise source is connected, like mains wiring, wiring connected to
> whatever the source is connected. The relative field strength will
> depend on the spectrum of what is created inside the device, and the
> radiation efficiency of that random collection of conductors that
> constitute the antenna. :)
>
> Hence my advice when encountering noise is to 1) carefully sniff the
> source and that wiring with a battery operated radio in the frequency
> range of the noise; and 2) start applying chokes to wiring at the source
> until noise is no longer sniffed on nearby wiring. My favorite sniffer
> is a Kenwood TH-F6A talkie with wideband RX. It's not very sensitive,
> but plenty good enough for up-close sniffing. Below 10 Mhz it
> auto-switches to a built-in loop stick, and there's a software switch
> between the loop and the antenna jack.
>
> Inexpensive alternatives sold under the Tecsun brand will get you from
> the AM BC band to 30 MHz and FM broadcast, and one of their higher
> priced models will get you greater sensitivity and the AM aircraft band
> above that. One of those higher priced models (in the $150 range) was
> reviewed by ARRL Labs about 10 years ago.
>
> 73, Jim K9YC
>
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>
--
*Dave - WØLEV*
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