The noise floor from Boltzmannian theory is, ISTR, -174dBm/Hz.

That is, per Hz of Bandwith.

Therefore, 3.4 kHz of BW will give you an increase of +35.3 dB,
giving you theoretical a noise floor of -138.7dBm, which you must
then degrade by the noise contributions from the RX itself.

"Al" wrote in message
...
In QST Jan 2000 the ARRL published some specifications about receivers
including the Icom R75. Regarding the R75 it stated that the Noise Floor
(mds) is -130dBm under certain specific conditions. It also states that
the
AM Sensitivity, 10dB (S + N)/N, under the same conditions is 1.7uV.