(Radio Frequency Interference)

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RFI is one of the most serious problems faced by amateur radio operators, who are always interested in working with weak received signals. RFI can originate from many sources - power lines, electric motors, televisions, and now increasingly from computers, networks, and other digital devices. RFI is an important aspect of "Electromagnetic Compatibility" (EMC), which aims to ensure that electronic devices enjoy peaceful coexistence with each other.

This page is meant to be a resource for hams interested in understanding and eliminating RFI problems.


The radio astronomy community is extremely concerned with RFI, because they operate very large instruments with exquisite sensitivity. Most radio astronomy is done at VHF frequencies and above, but some research is done down to "decametric" wavelenths -- HF. In the USA, the National Radio Astronomy Observatory is a primary resource. Note the following items of interest to hams:


The most common type of computer networking is based on Ethernet, which is now mainly seen in two forms - 10baseT and 100baseT. They normally use unshielded twisted pair (UTP) cabling (e.g., CAT5), and they operate at 10 or 100 MHz clock rate, respectively. Most new computer hardware supports 100baseT.

I have taken measurements of the 100baseT signal spectrum, and Fraser, G4BJM, has contributed some off-the-air measurements of a live Ethernet system. See the Ethernet details page.

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