On Sat, 29 Jul 2006 18:28:45 +0200, Karl-Arne Markstr?m wrote:
>In a radio context, the proper use of dBu is as a field strength
>value, where 0 dBu corresponds to a field strength of 1 microvolt/meter
Yes, a Google search shows this in the US FCC regulations. Like I said,
"There are many reference levels tied to dB expressions of voltage and
power, and all of them have their place as long as you understand what
you are measuring or specifying." The field strength reference is simply
another very good one that uses the same nomenclature (symbol) as the
pro audio definition for circuit voltage.
One problem, of course, is that we run out of letters when establishing
various mathematical definitions of physical realities. In addition,
engineers and scientists who choose the letters are often "Balkanized"
in their scientific background -- that is, audio guys and digital guys
tend not to know much about RF, and vice versa.
The letter "Q" has a familiar meaning to any analog circuit engineer --
it relates the loss component and bandwidth of a resonant circuit. But
in electroacoustics, the letter "Q" is used to describe the directivity
of a loudspeaker, and this definition has NOTHING to do with loss or
bandwidth. This gets very confusing, because audio engineers are also
concerned with the bandwidth of resonant circuits and filters. :)
In the case of the field strength usage of "dBu" (0 dBu = 1uV/m), the
behavior of the receiving antenna is part of the relationship between
that field strength and the power and voltage at the receiver input.
That makes any use of this field strength dBu to describe receiver
performance completely non-sensical.
>It appears that dBu and dBuV are used interchangeably in at least
>Japanese receiver literature and specifications as elaborated in
>the "Decibels" section of
>http://www.radiomods.co.nz/kenwood/kenwoodgeneral.html
>where a conversion table is provided together with some more
background.
There's a lot of nonsense on this webpage (which, it should be made
clear, is NOT a product of Kenwood). Also, literature tends to be
written by marketing folks, few of which are known (or hired) for their
technical acumen. And even if a technical type did write it, he/she is
likely to have the same "Balkanization" issues noted above.
73,
Jim Brown K9YC
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