--- In [email protected], Bob Dengler <[EMAIL PROTECTED]>
wrote:
"...OK, so does this mean the noise temperature of a NBFM FM receiver
can be approximated by measuring the 12 dB SINAD point & then
subtracting 4 dB? ..."
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Essentially - yes.
Given that it is generally accepted that:
N=kTB and that N= -174 dBm/Hz [at room temperature]
The 'accepted' value for the noise power in your receiver bandwidth
will be -133 dBm.
If your receiver has a measured 20 dB quieting of 0.35 microvolts
[-116 dBm] and a corresponding 0.25 microvolt 12 dB SINAD [-119 dBm]
then it follows that it has a Noise Figure NF = 10 dB [-119 minus 4 =
-123, -133 minus -123 = 10]
Keep this in mind when someone tells you they have a super pre-amp on
their repeater receiver and their receiver sensitivity is better than
a tenth of a microvolt - they are either using faulty measuring
procedures or poorly calibrated instruments because 20 dB quieting
would be on the order of 0.11 microvolts if the noise figure was zero.
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