Calculation of received noise power given ENB and ENR

At Effective noise bandwidth – IC-7300 SSB Rx Filter2 (2400Hz) the ENB of the receiver was measured at 2088Hz. This article goes on to calculate the power received from a Elecraft N-Gen noise source which has been measured to have Excess Noise Ratio (ENR) at 10.1MHz of 48.2dB.

Lets input the data to Field strength / receive power converter and find the received power.

The measurement is made is preamp off (so that the S meter is more realistic), and the supplied NoiseFigure is a guess… but the noise source is so strong (being some 30+dB above the receiver internal noise) that the result is barely sensitive to that assumption.

The calculator returns many results, we are interested in just the receive power in dBm. The results follow.

Field strength / receive power converter – results
N-GEN – IC-7300 (preamp off, FIL2:2400Hz soft)
26/08/2017, 10:21:33 (v2.02)
 

Frequency 10.100 MHz
Field Strength Bandwidth 2088.0 Hz
Field Strength distance to source 1.000 m
Noise Figure 48.200 dB
Noise Temperature 1.916e+7 K
Excess Noise Ratio 48.200 dB
Field Strength (2088.0 Hz) 1.723 μV/m
4.72 dBμV/m
0.004573 μA/m
-46.80 dBμA/m
7.88e-15 W/m^2
-141.04 dBW/m^2
Normalised Field Strength (1 Hz) -28.47 dBμV/m
-79.99 dBμA/m
3.77e-18 W/m^2
3.77e+4 SFU
3.77e+8 Jy
Antenna Factor -9.69 dB/m
Receiver input resistance 50.0 Ω
Receiver Bandwidth 2088.0 Hz
Receiver distance to source 1.000 m
Receiver Voltage (external) 5.255 μV
14.41 dBμV
Receiver Power (external) 5.524e-13 W
-92.58 dBm
1.916e+7 K
Receiver S/N 33.3 dB
S/N degradation 0.00201 dB

The key measure is Receiver Power (external) which is -92.58dBm. This is approximately 20dB lower than S9 (-73dBm) so one might expect an S meter reading of a little less than S6 using the convention that S points are 6dB apart. Unfortunately S meters are rarely accurately calibrated, and they rarely response to average power but tend to have a quasi-peak response and so read somewhat higher on white noise than for the same power in a continuous wave.