Custom Search
Over 10000 Pages Indexed
Your Host
Click here to read about RF CafeKirt
Blattenberger

... single-
handedly
redefining
what an
engineering website
should be.

View the YouTube RF Cafe Intro Video Carpe Diem!
(Seize the Day!)

5CCG (5th MOB):
My USAF radar shop

Hobby & Fun

Airplanes and Rockets:
My personal hobby website

Equine Kingdom:
My daughter Sally's horse
riding business website -
lots of info

•−•  ••−•    −•−•  •−  ••−•  •
RF Cafe Morse Code >Hear It<

Job Board

About RF Cafe©

RF Cafe E-Mail

Digital Communications Basics
RF Cafe Quiz #23

| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 |
| 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 |
| 42 | 43 | 44 | 45 | 46 | 47 | 48 | 49 | 50 | 51 | 52 | 53 | 54 |
| 55 | 56 | 57 | 58 | 59 | 60 | 61 | 62 |

All RF Cafe quizzes would make perfect fodder for employment interviews for technicians or engineers - particularly those who are fresh out of school or are relatively new to the work world. Come to think of it, they would make equally excellent study material for the same persons who are going to be interviewed for a job.

Some of these books used in quizzes are available as prizes in the monthly RF Cafe Giveaway.

Note: Many answers contain passages quoted from the text.


This quiz challenges your knowledge of digital communications basics.



1.  What is meant by binary frequency shift keying
     (BFSK)?

a)  Shifting two frequencies to key a microphone
b)  Using two distinctly different frequencies to represent digital 0s and 1s
c)  Shifting digital information at a binary frequency
d)  Half of quadrature shift keying



RF Cafe - Quiz 232.  The constellation to the right indicates what type of modulation?

a)  QPSK
b)  OQPSK
c)  MSK
d)  Orion






3.  What is the primary benefit of offset QPSK (O-QPSK) over QPSK?

a)  Greater efficiency
b)  Easier to code
c)  Constant envelope power
d)  No benefit



RF Cafe - Quiz 234.  What is the phase shift for the QPSK modulator block diagram to the right?

a)  0°
b)  45°
c)  90°
d)  180°






RF Cafe - Quiz 23 (borrowed from Wikipedia)5.  What is the image to the right an example of?

a)  Tropospheric waveguiding
b)  A VCO output
c)   A Spirograph drawing
d)  An eye pattern








6.  What is the purpose of the lowpass filter (LPF) in the QPSK modulator shown in Question 4?

a)  Prevents DC from entering the mixers
b)  Limits the bandwidth of the transmitted signal
c)  Adds a DC component to the signal
d)  Serves no purpose













RF Cafe - Quiz 237.  What is the spectrum to the right an example of?

a)  Frequency Hopping Spread Spectrum
b)  Octary Shift Keying (OSK)
c)  8-PSK
d)  Bi-Quadrature Shift Keying



8.  Which of the following items affects the bit error rate (BER) of a received signal?

a)  Oscillator phase noise
b)  Baseband filtering
c)  Carrier suppression
d)  All the above



9.  Which of these issues presents a problem for zero-IF (direct conversion) receivers?

a)  LO leakage creating a DC offset voltage
b)  Mixer flicker noise is included in the baseband signal
c)  2nd-order intercept products
d)  All the above



10. What is the Z-transform of the Dirac delta function, δ[n] ?

a)  1
b)  RF Cafe - Quiz 23
c)  RF Cafe - Quiz 23
d)  ∞


Need some help? Click here for the answers and explanations.

A Disruptive Web Presence

Custom Search
Over 10,000 pages indexed! (none duped or pirated)

Read About RF Cafe
Webmaster: Kirt Blattenberger
    KB3UON

RF Cafe Software

RF Cascade Workbook
RF Cascade Workbook is a very extensive system cascaded component Excel workbook that includes the standard Gain, NF, IP2, IP3, Psat calculations, input & output VSWR, noise BW, min/max tolerance, DC power cauculations, graphing of all RF parameters, and has a graphical block diagram tool. An extensive User's Guide is also included. - Only $35.
RF system analysis including
frequency conversion & filters

RF & EE Symbols Word
RF Stencils for Visio

Product & Service Directory
Personally Selected Manufacturers
RF Cafe T-Shirts & Mugs

RF Cafe Software

Calculator Workbook
RF Workbench
Smith Chart™ for Visio
Smith Chart™ for Excel