**HP Prime and HP 42S: Noise Figure and Noise Voltage**

*Notes: The programs for the HP 42S format are designed to work with the HP 42S’s solver. The programs were created using Thomas Okken’s Free42, and should also be compatible with the Swiss Micros DM42.*

**Noise Figure**

Given system temperature (in Kelvins), this program calculates the noise figure (in Decibels), which describes the noise performance of an amplifier. The noise figure is described as the difference between the noise output of an actual receiver to an ideal, noiseless receiver. A noiseless receiver is said to have a resistor operating at room temperature, 290 K (about 16.85°C or 62.33°F). The lower the noise figure, the better.

Formula:

F = 10 * log(T/290 + 1)

where:

F = noise figure (dB)

T = system temperature (K)

**HP Prime Program Function: NOISEDB**

EXPORT NOISEDB(T)

BEGIN

// Noise Figure in dB

// Input: T: Temperature (K)

// 2019-01-04 EWS

10*LOG(T/290+1);

END;

**HP 42S Program for Solver: NSEFG**

00 { 35-Byte Prgm }

01▸LBL “NSEFG”

02 MVAR “F”

03 MVAR “T”

04 RCL “T”

05 290

06 ÷

07 1

08 +

09 LOG

10 10

11 ×

12 RCL “F”

13 –

14 END

Example (Fix 4):

Input: T = 57.8°F, convert it to Kelvins, enter 287.4833 K (approximately)

Result: F = 2.9914 dB

**Noise Voltage**

Given the noise bandwidth (in Hertz) and the resistance (in Ω), calculate the open-circuit voltage (in RMS volts).

Formula:

e_n = √(1.6*10^-20 * B * R)

where:

e_n = open circuit voltage noise (RMS volts)

B = bandwidth (Hz)

R = resistance (Ω)

**HP Prime Program Function: NOISEVOLT**

EXPORT NOISEVOLT(b,r)

BEGIN

// Noise Voltage in V

// Input: B=bandwidth (Hz)

// Input: R=resistor (Ω)

// input numbers only

√(1.6ᴇ−20*b*r);

END;**HP 42S Program for Solver: NSEVT**

00 { 37-Byte Prgm }

01▸LBL “NSEVT”

02 MVAR “B”

03 MVAR “R”

04 MVAR “En”

05 16ᴇ-21

06 RCL× “B”

07 RCL× “R”

08 SQRT

09 RCL- “En”

10 .END.

Example (FIX 4):

Input: B = 31,000 Hz, R = 950 Ω

Result: e_n = 6.8644e-7 V

Sources:

Ball, John A. __Algorithms For RPN Calculators__ John Wiley & Sons: New York 1978. ISBN 0-471-03070-8

Eddie

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