Tuesday, June 28, 2011

BroadBand , PassBand ,BandPass , BaseBand & BandSTOP!

Salam alaikom,

Currently going through my favourite subject which is Computer networks ( networking engineering or telematics), actually preparing for a retake which will be held on thursday as last exam for the year! actually the one befor the last. the last is digital signal processing which is a story for another day.
 so i wanted to pass to you 4 definitions of terms which always played tricks on me.

It is a telecommunication technique used to determine the capasity of data transmission. It allow multiple channels to be used within one bandwidth of a medium (i.e coaxial cable). The best example of broadband is the Tv cable. The cable is broadband. Why? because the bandwidth of the cable can view more then one channel. So when you  are changing MTV to Peace Tv actually you are changel frequency to frequency. This method Tv cable method is called Frequency-Division-Multiplexing. Because the bandwidth is divided (multiplexed) to differenct channels\frequencies.  This method deals with analog signals only.
   BroadBand can be seen as a multiple of basebands.

It is a telecommunication technique used to determine the capasity (bandwidth) of data transmission. Over one bandwidth of the medium One communication happens. One types of information. i.e Only one phone call.
In low pass filters. the term is also used to describe the frequencies from zero to the Cut-off frequency. ( the frequencies which are passed).
  Ethernet (802.3) uses baseband because it is simpler.

it is a filter which is a combination of low pass filter and high pass filter so it passes a bandwidth u set by setting the values of the components you use to make up the circuit . It can be constructed of LCR or RLC.


Is the frequency passed through a bandpass filter. also can be caalled as BandPass signal.

It is a filter which rejects a range of frequency and passes others. It is also called Notch filter. Notch filter is used to remove the 50Hz. 50Hz in many cases us noise( unwanted signal) which is generated from the outlets or power supply.
That is simply what it is. You can dive deeper in it. Consider the above as a starter. At the moment of writing this article i was concerned about knowing the difference between Broadband(modulation) and badeband transmission because it is related the the PHYSICAL LAYER in the OSI module. because the physical layer is more concerned with the capacity of transmitting. Which makes for instance a fiber optic different from coaxial cable. Both are same as medium in term of propagating information.


Monday, June 6, 2011

Optics and Ibn Al-Haitham ??

This article is missing the revolutionary contribution of Ibn Al-Haitham in optical engineering , as the case usually when it comes to the Islamic scientists contribution to the modern world. Which i don't understand why. keeping the mainstream ideas about islam as terrorists specialists and that's all.
i will add extra information once i am done with the exams , say next month .

Friday, June 3, 2011

Stereo ..... Frequency Levels

What is a stereo ? 
i came across this question when trying to understand the Radio data system and how it works on . while reading this (RDS operates by adding data to the baseband signal that is used to modulate the radio frequency carrier. The baseband signal consists of a number of components. Firstly there is the mono audio consisting of the left plus right (L+R) component that is transmitted at the normal audio frequencies up to 15 kHz. The stereo difference signal is then amplitude modulated as a double sideband suppressed carrier signal at 38 kHz).
ok . there are two kind of stereos

Audio stereo and Video stereo

both refers to a similar term

Audio stereo : stands for sound being dividied into two separate channels (speakers) for the aim to support the sound simultaneously in two speakers to also provide the chance to mix different sounds. the idea is inspired because a human has two ears trying to make it realistic as much as possible. such as in a movie when a car passes the audio is divided in a way to give a sound (Doppler) from an ear to ear as the car is realistically passing in front of the audience.

Video stereo : two saperate images of the same objects, being taken slightly different in order to simulate 3D view for human eye. there are many different ways to get to the 3d effect which i wont discuss here

here is a good illustration klik here
Frequency levels
there are three weeks ahead of me to end the third year of applied communication engineering , one year ahead of graduating and i still do not know under what frequency lies the low , high frequency!!!! but i do know that microwave(not the range but the one u use ate your house) is the most used frequency in the world 2.4 gigahertz 

Free-space Wavelengths
Very Low Frequency
9 kHz - 30 kHz                               
33 km - 10 km
Low Frequency
30 kHz - 300 kHz
10 km - 1 km
Medium Frequency
300 kHz - 3 MHz
1 km - 100 m
High Frequency
3 MHz - 30 MHz
100 m - 10 m
Very High Frequency
30 MHz - 300 MHz
10 m - 1 m
Ultra High Frequency
300 MHz - 3 GHz
1 m - 100 mm
Super High Frequency
3 GHz - 30 GHz
100 mm - 10 mm
Extremely High Frequency
30 GHz - 300 GHz
10 mm - 1 mm
After having a short talk with Boumester (my teacher, i think i spelt it wrong :D) he recommended to take a look on RDS and SDR.
SDR software defined radio 
RDS radio data system 
I will lay it briefly to you

replaced the hardware with software which is abvious from its name. through the MEM technology lots of chips became cheaper and available which made it replace alot of analog equipments , in this radio specifically a microchip will replace a
IF amplifier or base band(any frequency from the lowest upto the cut-off frequency)
demodulator (in the receiver part to separate the signal from the carrier)
modulator (in the transmitter part to give the signal a carrier)

it uses lots of digital signal processing (the microchip does the mathematical operations)
In some application there will be after the antenna (in the receiver part) a bandpass filter and amplifier
an amplifier is used to amplify the nanowate and microwat received signals. and it is very know to any engineer or hobbyist that a homemade antenna (say a wire) can receive signals from unknown sources (spurious emissions) therefore the bandpass filter is used to get rid off such signals and pass the wanter bandwidth, without it the amplifier will amplify all the unwanted and wanted signals.

RDS :it is the tool which shows on the digital radio screens the basestation (1oo,  99.9) also can show the time and the name of the song.

I may include further information in the next days because this is all what i know for the moment , and i have to make a decision on which subject i may write a report on the system level.

for now i guess i will go for RDS because of the time constraints. (having exams in two weeks and not prepared at all :S) .