On 2/15/2022 1:40 PM, James Wolf wrote:
It seems from observation that much of the noise is generated in the monitor
power supply.
Yes. About 20 years ago, a law or other regulation was passed that
required almost anything that plugs into AC must use a switch-mode PSU
to reduce power consumption. Unfortunately, this is universally followed
because they're cheaper to build, but since Part 15 Rules are
unenforced, it's also cheaper to not worry about the noise they produce.
Some monitors use an external supply where you can ditch the
manufacturer's supply and put in an analog DC source. Typically 19 VDC.
As screens have gotten larger, DC power voltages have risen. I and
several friends were lucky to buy monitors designed for 14VDC, which run
fine on 12V batteries.
Some monitors are noisy from circuitry other than the PSU. Especially at
HF, the noise is conducted to cables connected to them, which act as
transmitting antennas. In the worst designs, the noise also radiates
from internal wiring.
FWIW, I never trust any assessments that any given product is quiet,
because most of us are surrounded by dozens noise sources, both in our
own homes and those of our neighbors. I use a vintage Kenwood talkie
that has a receiver that goes down below the AM broadcast band to listen
right next to a product, and also move along any cables connected to it.
73, Jim K9YC
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