Choke Cookbook for the 160 – 10M Bands using Fair-Rite #31 2.4″ od and 4″ od Toroids
Common mode chokes are added as series elements to a transmission link to kill common mode current.
The line may be a short one carrying audio or control signals between a computer and a radio, video between a computer and a monitor, noisy power wiring or feedlines for antennas.
This application note focuses on the use of chokes on the feelines of high power transmitting antennas to suppress received noise, to minimize RF in the shack (and a neighbor’s living room) and to minimize crosstalk between stations in multi-transmitter environments.
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Common Mode Chokes
Your ability to hear weak MF and HF signals is limited by noise, generated mostly by solid-state electronic switches within your own house, conducted via the 60-Hz power line to your shack, and from there to your antenna by common-mode current on the feedline. Putting common-mode chokes on your feedline, power and other cables will substantially reduce your received noise level. A good choke has 1 KΩ impedance for all MF and HF bands.
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