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.

I am trying to equate the two specs into the same units. -130dBm is equal to
0.071uV; 1.7uV is equal to -102.5dBm. That is a difference of 27.5dB.

It is my understanding (and this is where the fault probably lies) that 10dB
above the noise floor should put the signal at -120dBm, which is 0.22uV not
1.7uV. They are putting the signal at -102.5dBm. Where is the extra 17.5dB
loss coming from? Doesn't 10dB (S + N)/N mean 10dB above the noise?

All input is greatly appreciated. Thank you.

Al KA5JGV

On Mon, 14 Feb 2005 20:02:01 GMT, "Al"
wrote:
-130dBm under certain specific conditions

Hi Al,

Using the 500 Hz filter (not normally used in AM reception).

Comparing apples and donuts.

73's
Richard Clark, KB7QHC

"Al" bravely wrote to "All" (14 Feb 05 20:02:01)
--- on the heady topic of "Confused About Noise Floor and Sensitivity"

Al From: "Al"
Al Xref: aeinews rec.radio.amateur.antenna:5148

Al In QST Jan 2000 the ARRL published some specifications about receivers
Al including the Icom R75. Regarding the R75 it stated that the Noise
Al Floor (mds) is -130dBm under certain specific conditions. It also
Al states that the AM Sensitivity, 10dB (S + N)/N, under the same
Al conditions is 1.7uV.
Al I am trying to equate the two specs into the same units. -130dBm is
Al equal to 0.071uV; 1.7uV is equal to -102.5dBm. That is a difference of
Al 27.5dB.
Al It is my understanding (and this is where the fault probably lies)
Al that 10dB above the noise floor should put the signal at -120dBm,
Al which is 0.22uV not 1.7uV. They are putting the signal at -102.5dBm.
Al Where is the extra 17.5dB loss coming from? Doesn't 10dB (S + N)/N
Al mean 10dB above the noise?
Al All input is greatly appreciated. Thank you.

Al Al KA5JGV


I think it's a typo I calculated 0.775uV not 1.7uV. They might have
added a 1 in front of the decimal instead of a zero.

A*s*i*m*o*v

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.