Its Gourab
abt Mobility
We all know that electron mobility is higher than that of the holes . But why ?
Someone told me that its due to electron mass is less compared to hole. But here also the question arise how electron mass can be greater than that of hole while the hole only exist only when electron moves from a bond ???????????
Thursday, April 2, 2009
Electron Mobility, Electron Mass
Its Gourab
abt Mobility
We all know that electron mobility is higher than that of the holes . But why ?
Someone told me that its due to electron mass is less compared to hole. But here also the question arise how electron mass can be greater than that of hole while the hole only exist only when electron moves from a bond ???????????
abt Mobility
We all know that electron mobility is higher than that of the holes . But why ?
Someone told me that its due to electron mass is less compared to hole. But here also the question arise how electron mass can be greater than that of hole while the hole only exist only when electron moves from a bond ???????????
Electron Mobility, Electron Mass
Its Gourab
abt Mobility
We all know that electron mobility is higher than that of the holes . But why ?
Someone told me that its due to electron mass is less compared to hole. But here also the question arise how electron mass can be greater than that of hole while the hole only exist only when electron moves from a bond ???????????
abt Mobility
We all know that electron mobility is higher than that of the holes . But why ?
Someone told me that its due to electron mass is less compared to hole. But here also the question arise how electron mass can be greater than that of hole while the hole only exist only when electron moves from a bond ???????????
Friday, March 13, 2009
ANSWER: Satellite, Satellite Antenna
KRuNaL
Re: Sasmita
Satellite receiving antenna should have large aperture such that it can receive maximum signals......Means that antenna should have large beamwidth (B).......that for receiving case.....thtz in case of parabolic reflector also......okay?.....
If point to point communication between earth station n space segment is there, beamwidth should b narrow so that ther can possible maximum power radiated between those satellites......
okay......if neone here......share ideas abt thz
---
RP
Re: Smita Further
My ideas are: Parabolic antenna is by far the most generic, and high gain antenna as Krunal has suggested. Best suited for long range communications. Only one that beats it is Yagi Uda and Spiral antennas in specific cases. Yagi Uda cannot be used because of its size and other limitations, although in many cases we DO use that, but then spiral goes out of the whack when there is a little shift in polarization (circular) of signal. Which by the way is extremely easy to do, with changing air density and hence changing impedence along way to space. With both these
gone, we use parabolic.
----
$udipto....
sasmita: parabolic shape of rx antenna......
For a rx. antenna it is necessary to accumulate signals in a greater extent ,so that the beam area under the major beam lobe as much as possible. in parabolic reflecting antennas a property of light is being used, the reflective property. as the antenna is parabolic in nature, when signals fall in the dish, the dish reflect the signal in a converging manner. at the center of the antenna a sensor (receiver) is placed and it get the signal with high intensity... so a high accuracy signal is being received.
But, in some cases yagi uda antenna is also used as rx. , because it is mainly an array of antenna(BSA or EFA), so its efficiency can be manipulated by adjusting the no. of array elements.........again, the size of an antenna should be optimized according to its efficiency......
---
Sasmita
thnx
@kk,rp thnx
@sudipto thnx 4 giving better knoweledge abt RF....(once my teacher asked
one of my frens in his seminar on such topic....why it's called radio frequency?).....
also thnx 4 the note onRx..
n yes the picturial view of ur description may found on this link
http://www.mlesat.com/antennas.html
(on d ad space)
Re: Sasmita
Satellite receiving antenna should have large aperture such that it can receive maximum signals......Means that antenna should have large beamwidth (B).......that for receiving case.....thtz in case of parabolic reflector also......okay?.....
If point to point communication between earth station n space segment is there, beamwidth should b narrow so that ther can possible maximum power radiated between those satellites......
okay......if neone here......share ideas abt thz
---
RP
Re: Smita Further
My ideas are: Parabolic antenna is by far the most generic, and high gain antenna as Krunal has suggested. Best suited for long range communications. Only one that beats it is Yagi Uda and Spiral antennas in specific cases. Yagi Uda cannot be used because of its size and other limitations, although in many cases we DO use that, but then spiral goes out of the whack when there is a little shift in polarization (circular) of signal. Which by the way is extremely easy to do, with changing air density and hence changing impedence along way to space. With both these
gone, we use parabolic.
----
$udipto....
sasmita: parabolic shape of rx antenna......
For a rx. antenna it is necessary to accumulate signals in a greater extent ,so that the beam area under the major beam lobe as much as possible. in parabolic reflecting antennas a property of light is being used, the reflective property. as the antenna is parabolic in nature, when signals fall in the dish, the dish reflect the signal in a converging manner. at the center of the antenna a sensor (receiver) is placed and it get the signal with high intensity... so a high accuracy signal is being received.
But, in some cases yagi uda antenna is also used as rx. , because it is mainly an array of antenna(BSA or EFA), so its efficiency can be manipulated by adjusting the no. of array elements.........again, the size of an antenna should be optimized according to its efficiency......
---
Sasmita
thnx
@kk,rp thnx
@sudipto thnx 4 giving better knoweledge abt RF....(once my teacher asked
one of my frens in his seminar on such topic....why it's called radio frequency?).....
also thnx 4 the note onRx..
n yes the picturial view of ur description may found on this link
http://www.mlesat.com/antennas.html
(on d ad space)
Satellite, Shape of Satellite Antennas
Sasmita
Q-satellite
hi, here is a query abt satellite.. may b it's a silly question but i donno the ans.u ppl are very experienced....n m juz a student.
why d satellite receiving antennas r parabolic in shape?
Q-satellite
hi, here is a query abt satellite.. may b it's a silly question but i donno the ans.u ppl are very experienced....n m juz a student.
why d satellite receiving antennas r parabolic in shape?
RF ID Project Help
RP
RF ID Project
Posted by ::::: Vijeta
RFID PROJECT
WANT HELP ON RFID PROJECT.. PLZ HELP !!
ANY SITE AVIALABLE FOR THAT???
DONT KNW FROM WHERE TO START ....
THANX
----------------------------
(Comments are welcome...)
RF ID Project
Posted by ::::: Vijeta
RFID PROJECT
WANT HELP ON RFID PROJECT.. PLZ HELP !!
ANY SITE AVIALABLE FOR THAT???
DONT KNW FROM WHERE TO START ....
THANX
----------------------------
(Comments are welcome...)
ANSWER: Super Heterodyne Receiver, Nomenclature
RP
Naming conventions
Since hetero - is two different things in one system. Heterodyne Receiver mixes two different frequencies to detect desired signal waves. One step further from this would be mixing "specifically" lower frequency - IF (intermediate freq) to high frequency - RF in receiver architecture (As is the case with Super Heterodyne Rx). One step further calls for a name "above", hence - Super.
People have named many such things in communications... sometimes in future this makes little sense. Consider for instance -
VLF (very low freq.)
LF
HF
VHF (very high freq.) that goes upto only 300MHz
then comes
UHF ultra high freq.
But we could not keep adding ultra ultra ultra, so comes RF!!!(Confusing..!!!!??? To me it is... :( atleast) as it is typically around 1GHz and beyond.
Thats my take on naming - please comment if you think otherwise.
---
Venkatesh
superheterodyne reciever
Hi All,
Super - means 'superimposition' of modulating wave over carrier wave so that it can carry it for a very long distance without fading.
Heterodyne - means 'mixing of RF signals with the frequency signals generated by the local oscillator'. The resultant waves are called IF frequencies (intermediate frequencies). The local oscillator adjusts itself in such a way that the difference between RF generated waves and local oscillator generated waves are always 455 KHz!. The IF section is followed by IF amplifer(amplifies IF signals), demodulator (demodulates the modulated wave back by bypass the carrier wave to ground!), audio amplifier (increases strength of demodulated wave) and power amplifier (amplifies power of demodulated wave so that is matches with the impedance of the loud speaker) so that it can drive the audio speaker of 4/8/12 ohms. This is w.r.t. to Superheterodyne AM reciever.
In FM reciever, the IF stage is followed by demodulator, limiter, de-emphasis stage and one more aditional stage of AFC is added which connectes IF stage and audio amplifier stage so that it maintains gain of audio signal constant.
De-emaphasis is a stage which makes the amplitude of high frequencies during reception high. During transmission exactly reverse process takes place which is called pre-emphasis (it makes amplitude of high frequencies more so that it does not produce noise during transmission).
Thanks and Regards
Venkatesh Dastikopp DE&CE and pursuing B.Sc (instrumentation).
---
$udipto....
RF frequencies...are not ultra ultra ultra........
hey mr. RP, i think rf freq.s are not ultra ultra ultra high freq. it can be named as super high freq.(SHF:3GHz-30GHz) and extremely high freq.(EHF:30GHz-300GHz)........
see the chart below:
ELF: extremely low frequency 3Hz to 30Hz (100'000km to 10'000 km)
SLF: superlow frequency 30Hz to 300Hz (10'000km to 1'000km)
ULF: ultralow frequency 300Hz to 3000Hz (1'000km to 100km)
VLF: very low frequency 3kHz to 30kHz (100km to 10km)
LF: low frequency 30kHz to 300kHz (10km to 1km)
MF: medium frequency 300kHz to 3000kHz (1km to 100m)
HF: high frequency 3MHz to 30MHz (100m to 10m)
VHF: very high frequency 30MHz to 300MHz (10m to 1m)
UHF: ultrahigh frequency 300MHz to 3000MHz (1m to 10cm)
SHF: superhigh frequency 3GHz to 30GHz (10cm to 1cm)
EHF: extremely high frequency 30GHz to 300GHz (1cm to 1mm)
now ur confusion should be clear.........
---
RP
Naming convention again
I am not mentioning that we got a confusion here for RF being called Ultra ultra ultra, rather it should have been. Thanks for the chart though. It is worth mentioning here and quite useful.
Reading again my comment will tell you that I am just mentioning that we usually "name things in a certain way". Its like in early days of UNIX it copy command was named dd instead of cc because it was already reserved for c-compiler. Just a lack of imagination.
What I am trying to explain by mention of frequencies is only, that you could have named Super-hetrodyne receiver something else as well. But since it came after the already existing fundamental idea of hetrodyne receiver, it was named as Superhetrodyne receiver.
Naming conventions
Since hetero - is two different things in one system. Heterodyne Receiver mixes two different frequencies to detect desired signal waves. One step further from this would be mixing "specifically" lower frequency - IF (intermediate freq) to high frequency - RF in receiver architecture (As is the case with Super Heterodyne Rx). One step further calls for a name "above", hence - Super.
People have named many such things in communications... sometimes in future this makes little sense. Consider for instance -
VLF (very low freq.)
LF
HF
VHF (very high freq.) that goes upto only 300MHz
then comes
UHF ultra high freq.
But we could not keep adding ultra ultra ultra, so comes RF!!!(Confusing..!!!!??? To me it is... :( atleast) as it is typically around 1GHz and beyond.
Thats my take on naming - please comment if you think otherwise.
---
Venkatesh
superheterodyne reciever
Hi All,
Super - means 'superimposition' of modulating wave over carrier wave so that it can carry it for a very long distance without fading.
Heterodyne - means 'mixing of RF signals with the frequency signals generated by the local oscillator'. The resultant waves are called IF frequencies (intermediate frequencies). The local oscillator adjusts itself in such a way that the difference between RF generated waves and local oscillator generated waves are always 455 KHz!. The IF section is followed by IF amplifer(amplifies IF signals), demodulator (demodulates the modulated wave back by bypass the carrier wave to ground!), audio amplifier (increases strength of demodulated wave) and power amplifier (amplifies power of demodulated wave so that is matches with the impedance of the loud speaker) so that it can drive the audio speaker of 4/8/12 ohms. This is w.r.t. to Superheterodyne AM reciever.
In FM reciever, the IF stage is followed by demodulator, limiter, de-emphasis stage and one more aditional stage of AFC is added which connectes IF stage and audio amplifier stage so that it maintains gain of audio signal constant.
De-emaphasis is a stage which makes the amplitude of high frequencies during reception high. During transmission exactly reverse process takes place which is called pre-emphasis (it makes amplitude of high frequencies more so that it does not produce noise during transmission).
Thanks and Regards
Venkatesh Dastikopp DE&CE and pursuing B.Sc (instrumentation).
---
$udipto....
RF frequencies...are not ultra ultra ultra........
hey mr. RP, i think rf freq.s are not ultra ultra ultra high freq. it can be named as super high freq.(SHF:3GHz-30GHz) and extremely high freq.(EHF:30GHz-300GHz)........
see the chart below:
ELF: extremely low frequency 3Hz to 30Hz (100'000km to 10'000 km)
SLF: superlow frequency 30Hz to 300Hz (10'000km to 1'000km)
ULF: ultralow frequency 300Hz to 3000Hz (1'000km to 100km)
VLF: very low frequency 3kHz to 30kHz (100km to 10km)
LF: low frequency 30kHz to 300kHz (10km to 1km)
MF: medium frequency 300kHz to 3000kHz (1km to 100m)
HF: high frequency 3MHz to 30MHz (100m to 10m)
VHF: very high frequency 30MHz to 300MHz (10m to 1m)
UHF: ultrahigh frequency 300MHz to 3000MHz (1m to 10cm)
SHF: superhigh frequency 3GHz to 30GHz (10cm to 1cm)
EHF: extremely high frequency 30GHz to 300GHz (1cm to 1mm)
now ur confusion should be clear.........
---
RP
Naming convention again
I am not mentioning that we got a confusion here for RF being called Ultra ultra ultra, rather it should have been. Thanks for the chart though. It is worth mentioning here and quite useful.
Reading again my comment will tell you that I am just mentioning that we usually "name things in a certain way". Its like in early days of UNIX it copy command was named dd instead of cc because it was already reserved for c-compiler. Just a lack of imagination.
What I am trying to explain by mention of frequencies is only, that you could have named Super-hetrodyne receiver something else as well. But since it came after the already existing fundamental idea of hetrodyne receiver, it was named as Superhetrodyne receiver.
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