[Amps] conversion scale from dbu to microvolts

[Jim Brown]

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