Forums

looking for broadband engineering info.

Started by Bowen T February 24, 2005
Hi, I am a programmer and DSP/audio engineer looking to get my foot in 
the door with the integrated services industry, particulary digital 
cable.  I'm actually back after about a year and a half of music school 
and military, over which time I did no engineering whatsoever.  I'm 
trying to fill this gap by learning my stuff as good as possible.  2 
questions:

1.  What is a more appropriate newsgroup for this kind of interest?

2.  The following are typical questions for applicants to a local 
company, for headend engineer technician.  I figure these are the topics 
I'm going to be focusing on as I begin.  I knew about 3 answers off the 
top of my head.  I was hoping some of you could evaluate what I wrote.  
Of course I want the other answers too, but I need context as well, so 
I'm really looking also for good sources to learn this kind of stuff. 
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Q. Please explain the purpose of modulators. Explain how carrier to 
noise is best managed at the modulator. 

A. Digital signals are like square waves in that they have a wide 
spectrum.  This is undesirable for transmission lines because 
attenuation and delay distortion are frequency dependent effects.  So 
baseband signalling is unsuitable except for slow speeds and short 
distances.  A modulator turns each DC level into a sine wave that 
retains its shape better across the transmission.  Change in DC level of 
the original signal is converted into a change in amplitude, frequency 
or phase (or a combination) in the modulated signal.  

Not sure about the C/N
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Q. How are RF signals combined in the headend? 

A. The cable TV signals are received by microwave or (I'm guessing more 
likely) satellite at the head end.  Each signal is multiplied by a 
carrier frequency to shift it to its designated place in the channel 
lineup.  This is FDM, frequency Division Multiplexing.  Broadcast TV 
signals are about 5 MHz in bandwidth but the carrier frequencies are 
spaced closer to 6MHz apart, to give some spacing between signals.
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Q. What are digital receivers used for in a state of the art headend? 
How is encyption to the receiver maintained? What does a digital signal 
delivered to a digital set-to-box look like (modulation and bandwidth)? 
Describe two ways a digital signal can be routed to the STB. 
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Q.Identify the key tests within a Proof of Performance. Explain how 
these test are done. identify the FCC expectations on performance for 
each of these test. 
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Q. Which wires are crossed when making a crossover ethernet data cable? 
Describe the difference in a router and a switcher. 

A. Not sure about the Ethernet question.

A router and a switcher perform several of the same functions, and the 
difference is in the level of intelligence.  A switcher is smarter than 
a hub in that it can selectively retransmit information based on network 
or machine addresses, unlike a hub which just retransmits any incoming 
signal back out on every other port.  A router generally implies a user 
interface or a programming language that can be used to program the 
machine to take advantage of more sophisticated routing algorithms or 
provide other services, like firewalls.
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Thanks for any help. --Bowen
"Bowen T" <chromatic_dragon@operamail.com> wrote in message
news:1109292683.c6f225c966a3973ef28163d13f123b0f@teranews...
> Q. Which wires are crossed when making a crossover ethernet data cable?
http://www.cabletron.com/support/techtips/tk0231-9.html
Try the SCTE 

www.scte.org


Mark