Jim said:
>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. <
Precisely. You can only define a receiver performance in field strength when it
has a buit in antenna, and then, only under very specific conditions.
It's normally considered that the measurement uncertainty on a radiated
measurement is +/-6dB, although you will do better in a good anechoic chamber -
maybe +/-3dB.
Some of this may be a degree of sloppiness, using 'dBu' where 'dBuV' is
intended, the 'u' being really a Greek letter 'mu'. I haven't seen 'dBu' used
over here to mean 'dBuV/m', though.
I suppose you could specify the gain of a receiving system in dBuV/m if you
specified the Antenna Factor, which is the number relating microvlts/meter to
volts at the receiver input. I believe they do that effectively for noise
emasurement, using a standard 9 foot long whip.
Also, look at the uses of 'mu'. In radio, as a shortened 'micro', or as the
'gain' of a vacuum tube. Then it's also used for refractive index and
coefficient of friction. No wonder there's confusion between disciplines at
times!
73
Peter G3RZP
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