Jim:
k=1.38E-23 J/K (Boltzmann's Constant)
T=298K (Room temperature in Kelvin)
B=1 MHz (Noise bandwidth)
Check units: kT has units of Joules (energy) and, hence, kTB has units of W
(power).
Hence, U=kTB=4.11E-15 Watts = -113.86 dBm (dB referred to 1 mW of power).
Therefote your memory was correct.
And, yes reduce the NBW by three orders of magnitude to 1kHz and the noise
floor becomes -144 dBm
73...Jeff KN2R
Jim Reid wrote:
> Hi,
>
> Need my memory jogged! I believe I recall that
> the kTB value, at near room temperature, and
> in a 1 mHz bandwidth, the formula will calculate to be
> -114 dBm of noise power -- is this correct? Or
> close. If so, and the bw were narrowed to 1 kHz,
> a 30 dB shrinkage, the noise power would then
> be -144 dBm. These numbers seem about correct.
> Appreciate a correction if I am not doing this right, hi.
> Yes, the correct units must be used, degrees K, but
> I have no reference out here to the value of Boltzman's
> constant, B.
>
> 73, Jim KH7M
>
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