Several Notes about my Blog. All illustrations can be enlarged by clicking on them. Secondly, when I talk of making noise measures I am taking readings at a time when the band is normally closed. That is, most measures are made at about 0500 to 0600 AM local time on 14037.5 with the transceiver in AM Mode at 9 KHZ Band Width…
On to the discussion.
One reason to employ Common Mode Chokes in feedlines is to reduce received noise levels. The noise comes from the numerous sources within the modern home. These sources can be wall warts, switching supplies in various home appliances or noise from others homes noise sources riding AC lines into your home. Common Mode Chokes are Bilateral. They inhibit noise from propagating up your feedlines in common mode and back into the feedline in transmission line mode and thus to your receiver. They also inhibit common mode currents from propagating downward into your home appliances, AC lines and telephones etc via common mode from your antenna.
The single biggest contributor to noise in my home was the Direct TV HD DVR unit. Second on my noise list was anything to do with DSL wiring. When I began this experiment with CMC transmission line chokes my received noise level was over S-9 in CW mode. I never recorded AM wide B/W mode. After migrating from a vertical antenna to horizontal, adding a properly choked feedline, performing a noise audit within my home using a portable receiver and B Field Loop and deploying ferrite material where needed, I am pretty happy with my received noise levels. The following chart was made with data I recorded over the last 30 or so days. My CW 500 Hz S Meter normally reads S-Zero. While AM 9 KHz reads as the chart indicates.
I was concerned about my noise levels following the change in feedline choke placement. The earlier design had chokes uniformly placed at 12 foot intervals along the whole of the feedline. The newer design lumped the chokes at the ends of the feedline with a 6 foot spacing. This resulted in using fewer chokes by 2 and the geometry change followed by an increase in received noise was disconcerting. However, the noise level increase appears to have been the result of installation occurring at the same time as a severe heatwave occuring here and that of course caused a spike in AC Distribution lines load. Longer term monitoring should reveal the truth.
The noise battle never ends. Sooner or later a neighbor will install a halogen lamp with a solid state transformer or other equally noxious polluter and the fight will begin again. However, in the meantime I will work em cuz I can hear em!
Thanks for reading. Best, Chas W7MAP/5