In the tutorial at the link posted, I wrote:
Evaluating Equipment For Noise: When someone tells you that XYZ
equipment produces no noise on the ham bands because he can’t hear any
noise in his radio, should you believe that the equipment is clean? NO!
The equipment may be noisy but is not heard because it is being covered
by other noise from the neighborhood. Figs 7 and 8 compare the daytime
80M spectra at K6GFJ in a San Jose residential neighborhood and K9YC 30
miles to the south in the Santa Cruz Mountains. The difference in the
noise floor is 10 dB. And it’s certainly not dead quiet in the
mountains, either – everything on the displays from both QTHs is noise
from either switching power supplies or other electronic sources.
Proximity to Antennas Is What Matters: Noise radiates from sources on
wires that are connected to noise sources, and enters our receivers via
our antennas. My SteppIR that’s up 120 ft and is 200 ft from the shack
doesn’t hear much noise from the shack, but the 160M Tee vertical only
25 ft from the operating position does. When someone tells you that a
particular model of internet router or video monitor sits next to his
power amp and there’s no RFI, ask him how far it is from his antennas,
not from his radio.
73, Jim K9YC
On Mon,4/11/2016 7:43 AM, Jim Sheldon wrote:
The switcher supplies for these 2 monitors appear to be virtually
noise free. At least I have not had any noise problems that I can
attribute to them and they have been on the desk for several years now.
My major noise source has always been the 7500 volt power lines that
run across the South and West sides of my small city lot. Fortunately
the utility company ran afoul of the FCC several years ago and they
are very responsive to noise/interference calls.
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