Noise and dB Calculations

COMMUNICATIONS

1. It is a form of external noise and happens when information signal from source produce frequencies that fall outside their allocated bandwidth and interfere with information signal from another source

• interference

2. It results when unwanted harmonics of a signal are produced through non-linear amplification (mixing).

• Harmonic distortion

3. This noise occurs whenever current has to divide between two or more electrodes and results from the random fluctuation in the division

• Partition noise

4. Calculate the spectrum density for a certain communication system with an IF bandwidth of 10.7MHz

• SN = 4x1-21W/Hz

SN = 1.38x10-23(290K)

5. The resistor R1 and R2 are connected in series at 300K and 400K temperatures respectively. If R1 is 200Ω and R2 is 300Ω, find the total noise over a bandwidth of 100kHz.

• 996.8nV

• Vn(total) = √Vn(1)2+Vn(2)

2

6. A transmission unit used in Northern European countries originally used to express the attenuation of the current along the transmission line.

• Neper (np)

7. It is the unit of measurement of noise power used in the Western Electric 144-type handset with sensitivity of -90dBm at 100Hz

• dBrn

8. When measuring a voice channel at a -4dB test point level, the meter reads -76dB. Calculate the reading in dBrnCO.

• 18dBrnCO

dBrnCO = dBrnC – 0TLP

=-76dBm + 90 – (-4dB)

9. A low frequency noise that seems to be associated with heavy-metal ion contamination

• Burst Noise

10. It is the American term for relative level point

• TLP/Transmission Level Point

11. A -42dBmp of noise at a -5dBr point would be reported as dBm0p

• -37dBm0p

dBm0p= dBmp – 0TLP

-42 - (-5)

12. What is the effect on the signal-to-noise ratio of a system if the bandwidth is doubled, considering all other parameters to remain unchanged except the normal thermal noise only. The S/N will be___.

• Decreased by ½

• 13. A diode generator is required to produce a 12µV of noise in a receiver with an input impedance of 75Ω and a noise power bandwidth of 200kHz. Determine the current through the diode in mA.

• 398mA

IN =√2qIoB , q= 1.6x10-19C, solve for Io

14. NIF stands for

• Noise Improvement Factor

15. Naturally occurring electrical disturbance that originate within the earth’s atmosphere.

• Static noise

16. Noise that is present regardless of whether there is a signal present or not.

• Uncorrelated noise

17. Industrial noise frequency is between

• 15 to 160 MHz

18.A figure of merit to measure the performance of a radiation detector.

• Noise Equivalent Power

19.Unit of noise power of psophometer

• pWp

20. 0 dBrn is equal to how many dBm at 1000 Hz.

• -90dBm