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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