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Old 02-09-2011, 03:04 PM   #15
Dave R
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Quote:
Originally Posted by Skip View Post
Very few modern sonar/depth finders have metal housings....most are plastic.

Additionally RF energy can be coupled into the device via the power leads. So a power lead that may be a derivative of the wave length of a particular RF transmitter could help induce interference into the device.

Finally a particular brand of Sonar may have an internal oscillator that is harmonically related to the frequency of the radar unit.

There are multiple ways/reasons that the particular device BI has, or the unique way that it is installed, could induce the particular interference he is seeing.

That's why marine electronics technicians that know what they are doing, and will work for a reasonable price, are a very scarce resource.

Finally this is why I beleive that while BI's claims are rare, they are plausible and verifiable in real world situations.
During my time working in Bell Labs, I did some electromagnetic interference and susceptibility testing on telecom gear. This is stuff that is carefully shielded to prevent interference and you would not believe the ways microwave radio waves can get into stuff. There's no requirement that a depth finder has to meet a susceptibility rating, so it would not surprise me at all if it could act as a radar detector.
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