Yeah image rejection probably wasn't the correct term (especially when an IF isn't involved) but it's hard to put into simple words when I haven't slept properly for 72 hours..
You know though what I mean...
BTW, cat5e specifies gigabit over a
maximum of 100m (between active devices) again that is dependant on environment and is not a guarantee and could run longer or could have problems a lot shorter.
As for normal environment it begs the question what do you consider normal? Most household equipment (especially older stuff) isn't regulated by emissions laws like office/data/telecoms devices