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.
Super Heterodyne Receiver, Nomenclature
$udipto....
why a super heterodyne receiver is called"super"?
any body plz tell me why super heterodyne receiver is named like such "super"?
why a super heterodyne receiver is called"super"?
any body plz tell me why super heterodyne receiver is named like such "super"?
ANSWER: Electron Mobility, Electron Mass
Naveen
mobility!!!
it might seem confusing to claim electronmobility is greater than hole mobility. infact it is true as for a a undoped semiconductor e mobility is twice hole's... HOW
its just the way we define holes and electrons
hole is a vacancy of electron...
but the electrons which generate holes and what we call hole current are different from the electrons that constitute wha we call electron current...
hole current is hue to electron vacancies in valance band...
electron current is due to flow of electrons in conduction band...
so the mobility issue is therefore obvious... hope thats clear...
---
ASH007
@ Gourab
Thanx to RP for posting this nice forum.
..............................................................
abt Mobility.........
........
It seems that ur confused about mobility between electron and holes, or positive charge and negative charge. It is well known that negative charge i.e. electron is highly mobile than positive charge i.e. ion because of its mass. Here positive ion is the molecule that lost one of its electron and got +ve polarity. Due to its bulky structure and mass 1800 times greater than electron become less mobile.
Whereas Hole mobility is virtual moment its is actually movement of electron leaving behind its vacancy.
---
Its Gourab
@ ASH 007 about Mobility
ASH 007 u write that ----------->
"electron is highly mobile than positive charge i.e. ion because of its mass. Here positive ion is the molecule that lost one of its electron and got +ve polarity. Due to its bulky structure and mass 1800 times greater than electron become less mobile."
U are making some confusion between +ve Ion & Hole . Holes r the absense of electron from a bond not the positve ion . Ok .
I have no confusion about electrons higher mobility ............ I am asking the reson behind that.
---
Its Gourab
Mobility !!! @ Naveen
Thnx 4 ur reply.
But !!!!!!! I am asking about the Reason of high mobility of electron than the holes, which is not clear frm ur post.
---
RP
Mobility
When we are talking about hole mobility we are not taking about positive ion mobility. So mass goes out of the window. Yes, the energy required to move a hole is much more than the electron, and that as has been vaguely pointed out in mails earlier is the leading cause of slow hole mobility, but physically, electron moves as a body, and hole moves as an empty space through the atomic structre with a pull against the move from all the atoms surrounding it.
Thats my thinking, that hole gets electric field exerted resistance from pull all around.
---
Its Gourab
But.......... RP
Hi Rp , u told that "hole moves as an empty space through the atomic structre with a pull against the move from all the atoms surrounding it. "
Hole is a empty space is right. But holes faces a pull to move ? Why ????????
---
RP
@mobility
posted question outside forum for better visibility - I think you need quantitative analysis Gaurab. I am sure there is a lot of stuff on this one, but I am rusty. Dont remember right now correctly, and cannot also see any links explaining this mathematically quickly.
Lets see if anyone here in Forum or outside can reply!!!
---
Naveen
Hi Gaurab...
Its obvious that electron in conduction band is more mobile than that in Valence band.... What more to explain on that.... Valence band is tied to atom...
mobility!!!
it might seem confusing to claim electronmobility is greater than hole mobility. infact it is true as for a a undoped semiconductor e mobility is twice hole's... HOW
its just the way we define holes and electrons
hole is a vacancy of electron...
but the electrons which generate holes and what we call hole current are different from the electrons that constitute wha we call electron current...
hole current is hue to electron vacancies in valance band...
electron current is due to flow of electrons in conduction band...
so the mobility issue is therefore obvious... hope thats clear...
---
ASH007
@ Gourab
Thanx to RP for posting this nice forum.
..............................................................
abt Mobility.........
........
It seems that ur confused about mobility between electron and holes, or positive charge and negative charge. It is well known that negative charge i.e. electron is highly mobile than positive charge i.e. ion because of its mass. Here positive ion is the molecule that lost one of its electron and got +ve polarity. Due to its bulky structure and mass 1800 times greater than electron become less mobile.
Whereas Hole mobility is virtual moment its is actually movement of electron leaving behind its vacancy.
---
Its Gourab
@ ASH 007 about Mobility
ASH 007 u write that ----------->
"electron is highly mobile than positive charge i.e. ion because of its mass. Here positive ion is the molecule that lost one of its electron and got +ve polarity. Due to its bulky structure and mass 1800 times greater than electron become less mobile."
U are making some confusion between +ve Ion & Hole . Holes r the absense of electron from a bond not the positve ion . Ok .
I have no confusion about electrons higher mobility ............ I am asking the reson behind that.
---
Its Gourab
Mobility !!! @ Naveen
Thnx 4 ur reply.
But !!!!!!! I am asking about the Reason of high mobility of electron than the holes, which is not clear frm ur post.
---
RP
Mobility
When we are talking about hole mobility we are not taking about positive ion mobility. So mass goes out of the window. Yes, the energy required to move a hole is much more than the electron, and that as has been vaguely pointed out in mails earlier is the leading cause of slow hole mobility, but physically, electron moves as a body, and hole moves as an empty space through the atomic structre with a pull against the move from all the atoms surrounding it.
Thats my thinking, that hole gets electric field exerted resistance from pull all around.
---
Its Gourab
But.......... RP
Hi Rp , u told that "hole moves as an empty space through the atomic structre with a pull against the move from all the atoms surrounding it. "
Hole is a empty space is right. But holes faces a pull to move ? Why ????????
---
RP
@mobility
posted question outside forum for better visibility - I think you need quantitative analysis Gaurab. I am sure there is a lot of stuff on this one, but I am rusty. Dont remember right now correctly, and cannot also see any links explaining this mathematically quickly.
Lets see if anyone here in Forum or outside can reply!!!
---
Naveen
Hi Gaurab...
Its obvious that electron in conduction band is more mobile than that in Valence band.... What more to explain on that.... Valence band is tied to atom...
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 ???????????
Thursday, March 12, 2009
Displacement Current
RP
Ashish Agrawal::Displacement Current
@Ashish Agarwal:: Displacement Current
Lets define current first. Current is when charge passes through a plane.
Plane can be anything from being in space or for that matter opposite plate of the capacitor!
1. If we think of displacement current in physical/pure physics way - When you start charging one plate of cap, the other starts to get opposite charge. Energy is being passed from one point to other (simply speaking...rate of transfer of evergy, leads to power, leads to = I^2*R, where R is 337 Ohm aprox. and I is displacement current by the way... will come to this later). It will only happen in transient state, the energy travels on the back of the entity called displacement current. It is not something that just exists in equations to satisfy some void.
2. Since there is no energy flow, no power delivered, no change of potential from one value to other, there is literally no one doing anything in static field. Hence displacement current is non-existing in this case. If you read through any antenna or EM energy book, you'd come across the same guy that carries energy ahead.
I would want to mention though, when you place a static charge in space, from the instance it was placed to the instance it exists, that period is of "Step transient". Something green's function in mathematics defines such phenomenon. So there is no such perfect static field thing in nature.
So where ever you turn, you'll see displacement currents all around you... even in static fields... when they are propagating that is :)
Ashish Agrawal::Displacement Current
@Ashish Agarwal:: Displacement Current
Lets define current first. Current is when charge passes through a plane.
Plane can be anything from being in space or for that matter opposite plate of the capacitor!
1. If we think of displacement current in physical/pure physics way - When you start charging one plate of cap, the other starts to get opposite charge. Energy is being passed from one point to other (simply speaking...rate of transfer of evergy, leads to power, leads to = I^2*R, where R is 337 Ohm aprox. and I is displacement current by the way... will come to this later). It will only happen in transient state, the energy travels on the back of the entity called displacement current. It is not something that just exists in equations to satisfy some void.
2. Since there is no energy flow, no power delivered, no change of potential from one value to other, there is literally no one doing anything in static field. Hence displacement current is non-existing in this case. If you read through any antenna or EM energy book, you'd come across the same guy that carries energy ahead.
I would want to mention though, when you place a static charge in space, from the instance it was placed to the instance it exists, that period is of "Step transient". Something green's function in mathematics defines such phenomenon. So there is no such perfect static field thing in nature.
So where ever you turn, you'll see displacement currents all around you... even in static fields... when they are propagating that is :)
Antenna Design
RP
Akhil ::: Antenna design
First of your good reference can be Radio Frequency and Microwave Communication Circuits - Devendra Misra, if you are off to designing a complete transmission system. You need chapters 4, 5, and 10. The band you are talking about is not a "free" band though (I "THINK" it is not free for public - just a word of caution - be careful. 2.4 GHz is free, 5.5 GHz is free... try that ????)
You would already know this but Friis formula I think would be helpful for Antenna power calculations, but it would also be very important what your recevier system is going to be? The power amplifier you want, you can use most of GaAs/GaInAs based device. They would give you very good and cheap LoS kind of 1KM range. For my 5.5 GHz system I found it very useful. I also tried PHEMT EC2612 for Low Noise Amplifier on receiver end.
Akhil ::: Antenna design
First of your good reference can be Radio Frequency and Microwave Communication Circuits - Devendra Misra, if you are off to designing a complete transmission system. You need chapters 4, 5, and 10. The band you are talking about is not a "free" band though (I "THINK" it is not free for public - just a word of caution - be careful. 2.4 GHz is free, 5.5 GHz is free... try that ????)
You would already know this but Friis formula I think would be helpful for Antenna power calculations, but it would also be very important what your recevier system is going to be? The power amplifier you want, you can use most of GaAs/GaInAs based device. They would give you very good and cheap LoS kind of 1KM range. For my 5.5 GHz system I found it very useful. I also tried PHEMT EC2612 for Low Noise Amplifier on receiver end.
Signal Strength near oceans
RP
For Sai::::: signal strength near oceans
Since cellular towers are on land, minimal coverage is there towards seas.
Rivers, usually have lots and lots of trees near them. Trees are blobs of water hanging in air, because leaf's contain a lot of water. Water being extremely bipolar in nature absorbs EM energy, and we end up with poor/minimal signal there. Satellite signal is good on the sea level
usually very good, because satellite signal does not suffer any multipath or interference as it would in common cities. In clear sky atmosphere you receive good satellite signal strength but it is still worse than you would have in any vast plain field on land. Reason again is heavy evaporation causes signal loss...
Stark observation though on your part.
For Sai::::: signal strength near oceans
Since cellular towers are on land, minimal coverage is there towards seas.
Rivers, usually have lots and lots of trees near them. Trees are blobs of water hanging in air, because leaf's contain a lot of water. Water being extremely bipolar in nature absorbs EM energy, and we end up with poor/minimal signal there. Satellite signal is good on the sea level
usually very good, because satellite signal does not suffer any multipath or interference as it would in common cities. In clear sky atmosphere you receive good satellite signal strength but it is still worse than you would have in any vast plain field on land. Reason again is heavy evaporation causes signal loss...
Stark observation though on your part.
Gilbert Cell Multiplier
᪅ sundeepᇗ
what s the use of gilbert cell multiplier ?
------------------
(Comments are welcome)
what s the use of gilbert cell multiplier ?
------------------
(Comments are welcome)
ANSWER: Diode, Zener Diode
```` AREDEE ®™
NOT ANSWERED
Q...
Its Gourab
Diode
General diodes are made up of Si gerally and we operate this diodes generally in forward bias while Zener diode in the reverse bias . Is there any difference in the construction of this two diode i.e. I want 2 say why we use Zener diode only in the forward bias ?
ans:
we use zener in reverse bais only
nd yes construction of both diodes r same besides dopping level used for p-n material differs(heavilly dopped as concern to zener)
by sutably controling the amount of impurities & making p-n junc free from surface imperfection,the vtg at which breakdown takes place can b made to occur very distinctly&sharply
Once zener has broken down,very small change in vtg.across diode results change in current flowing thr it,so used as reff vtg.or in regulator ckts.too
Zener effect is only found in diodes th breakdown below ab6V in revere bais.
in this region diplection region is very narrrow.........
b-coz of exremely narrow deplection region there exists a high electric field across the junc. this elect.field provides a high elect.force which is responsible for tearing electrons out of the covalent bond directly rather th collision.This is the true ZENER effect so this is how it has to work in reverse bais only
NOT ANSWERED
Q...
Its Gourab
Diode
General diodes are made up of Si gerally and we operate this diodes generally in forward bias while Zener diode in the reverse bias . Is there any difference in the construction of this two diode i.e. I want 2 say why we use Zener diode only in the forward bias ?
ans:
we use zener in reverse bais only
nd yes construction of both diodes r same besides dopping level used for p-n material differs(heavilly dopped as concern to zener)
by sutably controling the amount of impurities & making p-n junc free from surface imperfection,the vtg at which breakdown takes place can b made to occur very distinctly&sharply
Once zener has broken down,very small change in vtg.across diode results change in current flowing thr it,so used as reff vtg.or in regulator ckts.too
Zener effect is only found in diodes th breakdown below ab6V in revere bais.
in this region diplection region is very narrrow.........
b-coz of exremely narrow deplection region there exists a high electric field across the junc. this elect.field provides a high elect.force which is responsible for tearing electrons out of the covalent bond directly rather th collision.This is the true ZENER effect so this is how it has to work in reverse bais only
Diode, Zener Diode
Its Gourab
Diode
General diodes are made up of Si gerally and we operate this diodes generally in forward bias while Zener diode in the reverse bias . Is there any difference in the construction of this two diode i.e. I want 2 say why we use Zener diode only in the forward bias ?
Diode
General diodes are made up of Si gerally and we operate this diodes generally in forward bias while Zener diode in the reverse bias . Is there any difference in the construction of this two diode i.e. I want 2 say why we use Zener diode only in the forward bias ?
555 IC
Its Gourab
To ---->>> abhishek - life
Hi friend.I glad to know that in IC 555 there r three 5kohm resistance in IC555. Thnx 4 that information . Will u plz tell m frm where u get it ?
----------
(Comments are welcome......)
To ---->>> abhishek - life
Hi friend.I glad to know that in IC 555 there r three 5kohm resistance in IC555. Thnx 4 that information . Will u plz tell m frm where u get it ?
----------
(Comments are welcome......)
ANSWER: 8085 Microprocessor Problem, Multivibrator
RP
Bistable Multivibrator
Abhi
In the basic analysis there is no difference in the transistors actually.
Think of transistors as power on and off switches. Just a glorified this : _/ _
So lets say we have transistros Q1 and Q2. When Q1 is on, that is: _._._
it shorts the high voltage signal to ground, and its output goes to zero.
Zero goes in to the Q2 keeping it off, that is _./ ._
Keeping the transistor open does not ground high voltage signal. This keeps output at high V. Which goes to input of Q1 and keeps it on all the time. Now this is a stable state, similar state which will be stable can be acheived by Q2 on and Q1 off. For two stable states it is bi stable
multivibrator.
I found a link to a good teaching aid for this. You may try
http://www.falstad.com/circuit/ex-multivib-b.html
---
deepak.m
Astable, Bistable And Monostable ckts ar
Astable, Bistable And Monostable ckts are used as counters, Timers as far as i know .If you found it further pls discuss.
Bistable Multivibrator
Abhi
In the basic analysis there is no difference in the transistors actually.
Think of transistors as power on and off switches. Just a glorified this : _/ _
So lets say we have transistros Q1 and Q2. When Q1 is on, that is: _._._
it shorts the high voltage signal to ground, and its output goes to zero.
Zero goes in to the Q2 keeping it off, that is _./ ._
Keeping the transistor open does not ground high voltage signal. This keeps output at high V. Which goes to input of Q1 and keeps it on all the time. Now this is a stable state, similar state which will be stable can be acheived by Q2 on and Q1 off. For two stable states it is bi stable
multivibrator.
I found a link to a good teaching aid for this. You may try
http://www.falstad.com/circuit/ex-multivib-b.html
---
deepak.m
Astable, Bistable And Monostable ckts ar
Astable, Bistable And Monostable ckts are used as counters, Timers as far as i know .If you found it further pls discuss.
8085 Microprocessor Problem, & Multivibrator
᪅ sundeepᇗ
hi friends.
i do have a great problem with 8085 microprocessor.
just now learning the basics.?
could you people help me to easily understand the concept.
one more.
do we use astable,monostable and bistable multivibrator in any electronic devices?
hi friends.
i do have a great problem with 8085 microprocessor.
just now learning the basics.?
could you people help me to easily understand the concept.
one more.
do we use astable,monostable and bistable multivibrator in any electronic devices?
ANSWER: A/D Converter, help
RP
A2D converter
There is nothing wrong with voltage divider I think. Should be optimum/cheapest solution if not best.
Do you think otherwise for some reason? If yes please share your thoughts...
---
Danish
THANX RP
YEAH U R RIGHT ITS A CHEAPEST SOLUTION BUT PROBLEM IS THAT MY SUPPLY VOLTAGE IS 3.20 V AND I NEED TO TAKE A HALF OF THIS SUPPLY VOLTAGE FOR
REFRENCE IF I USE SAME RESISTOR IN THE VOLTAGE DIVIDER I CAN GET HALF OF
THIS BUT HOW MUCH PRECISE IS THIS AND HOW CAN I STABILIZE THE DC VOLTAGE
WHAT DO U THINK RP
---
RP
@voltage divider - Danish
Is there way one can share diagrams here on orkut???
If not, I just wish if we could share pics...
Sorry people for my ignorance :( I consider myself tech savvy but some tools like orkut are fairly advance for my league :(
A2D converter
There is nothing wrong with voltage divider I think. Should be optimum/cheapest solution if not best.
Do you think otherwise for some reason? If yes please share your thoughts...
---
Danish
THANX RP
YEAH U R RIGHT ITS A CHEAPEST SOLUTION BUT PROBLEM IS THAT MY SUPPLY VOLTAGE IS 3.20 V AND I NEED TO TAKE A HALF OF THIS SUPPLY VOLTAGE FOR
REFRENCE IF I USE SAME RESISTOR IN THE VOLTAGE DIVIDER I CAN GET HALF OF
THIS BUT HOW MUCH PRECISE IS THIS AND HOW CAN I STABILIZE THE DC VOLTAGE
WHAT DO U THINK RP
---
RP
@voltage divider - Danish
Is there way one can share diagrams here on orkut???
If not, I just wish if we could share pics...
Sorry people for my ignorance :( I consider myself tech savvy but some tools like orkut are fairly advance for my league :(
A/D Converter, help
Danish
need help regarding A to D converter
hi guys i need to design a A to D converter i am using ads8345 but the problem is that i need to provide a refrence voltage which should be half of vcc .I have a question that is voltage divider is only solution for this to provide stabilize refrence voltage or is there any other option. Please help me out
need help regarding A to D converter
hi guys i need to design a A to D converter i am using ads8345 but the problem is that i need to provide a refrence voltage which should be half of vcc .I have a question that is voltage divider is only solution for this to provide stabilize refrence voltage or is there any other option. Please help me out
ANSWER: Why use AC?
RP
Why use AC
First reason of supplying AC to houses is historic. When Edison's company was sending electricity to houses in beginning, it was all DC. Later machines were produced that could produce electricity in much more efficient way and suppy at cheaper cost. Reason was obvious - Edison's rivals could use turbines to produce power with utmost ease and they could transmit power exteremly efficiently as AC uses sine waves.
Starting from that, transformers, stepping up and down of power became possible with AC, reducing the losses even further. Then there are other inherent advantages of AC such as you dont un-necessarily charge something up if a power cable is falling on something, there are ways to reduces losses in AC even further that are not at all there in DC and so on.
==========================
What really is a funny quiz question perhaps is - Current is defined as
"Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth.
So question is if this electron never reached the bulb in my house, how come it glows?
---
Roger
Why use AC? ..flashback
Mr. Edison, the inventor of the light bulb, strongly promoted DC (Direct Current) and was strictly against AC (Alternating Current). AC was invented by Nikola Tesla. AC was more economical to distribute over large distances as it had lesser distribution losses. The AC popularity fast caught up and hence it is used everywhere today.
However the trains in Mumbai still operate on DC (1500V). The railway ministry has realised that significant power is wasted and so has decided to use AC for trains. Disadvantage is that people traveling on rooftops will be electrocuted if AC is used, even if they are upto 2 meters away from the cable. Any idea why?
Roger
AC funny question + answer
This is in reply to RP's funny question.......nobody answered it till now. let me answer it :-).
==========================
Q) What really is a funny quiz question perhaps is - Current is defined as "Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth.
So question is if this electron never reached the bulb in my house, how come it glows?
Ans) Imagine there is a long pipe (the wire) that is completely filled with water (the electrons). Now what will happen if i push the water a little from one end of the pipe. The water on the other end of the pipe will immediately push forward. The reverse happens when i pull back the water. So even though the water molecules at one end of the pipe have not reached the other end, the molecules at the other end have moved back and forth. Thus energy transfer has taken place (i.e. moving of water molecules). I could use this energy to do some work, (e.g. turn a propeller).
This can also answer the 2nd funny question below
==========================================
Q) In case of Direct current, electrons move in a copper conductor at a speed of only 1/4mm per second. For such a slow speed it will take an electron several minutes to travel a few inches of wire between the battery and the bulb. How come then does the light bulb turn on instantaneously?
---
RP
Funny question - serious answer
Many a times funny questions pose fundamental aspect to be answered and people just dont answer it. Thanks for bringing it up Roger. What I wanted to promote was that every one around "teaches" current wrongly as when charge passes through a conductor. Where as it should be defined as charge passing through a plane in space. Then all things fall right in place.
Thanks for coming in to answer. Water hose analogy is really good in teaching simple, yet relevant concept. In 12th/13th chapter in Resnick-Halliday-Walker the chapter that described current in +2 (excuse me I have long forgot the chapters now :) long time) that was the only book I found that explained it correctly.
Why use AC
First reason of supplying AC to houses is historic. When Edison's company was sending electricity to houses in beginning, it was all DC. Later machines were produced that could produce electricity in much more efficient way and suppy at cheaper cost. Reason was obvious - Edison's rivals could use turbines to produce power with utmost ease and they could transmit power exteremly efficiently as AC uses sine waves.
Starting from that, transformers, stepping up and down of power became possible with AC, reducing the losses even further. Then there are other inherent advantages of AC such as you dont un-necessarily charge something up if a power cable is falling on something, there are ways to reduces losses in AC even further that are not at all there in DC and so on.
==========================
What really is a funny quiz question perhaps is - Current is defined as
"Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth.
So question is if this electron never reached the bulb in my house, how come it glows?
---
Roger
Why use AC? ..flashback
Mr. Edison, the inventor of the light bulb, strongly promoted DC (Direct Current) and was strictly against AC (Alternating Current). AC was invented by Nikola Tesla. AC was more economical to distribute over large distances as it had lesser distribution losses. The AC popularity fast caught up and hence it is used everywhere today.
However the trains in Mumbai still operate on DC (1500V). The railway ministry has realised that significant power is wasted and so has decided to use AC for trains. Disadvantage is that people traveling on rooftops will be electrocuted if AC is used, even if they are upto 2 meters away from the cable. Any idea why?
Roger
AC funny question + answer
This is in reply to RP's funny question.......nobody answered it till now. let me answer it :-).
==========================
Q) What really is a funny quiz question perhaps is - Current is defined as "Charge flowing through a conductor" in +2 physics books. Now in AC, typically an electron in power transmission wire moves merely 10 atoms far to a direction when it is called back to oscillate again back and forth.
So question is if this electron never reached the bulb in my house, how come it glows?
Ans) Imagine there is a long pipe (the wire) that is completely filled with water (the electrons). Now what will happen if i push the water a little from one end of the pipe. The water on the other end of the pipe will immediately push forward. The reverse happens when i pull back the water. So even though the water molecules at one end of the pipe have not reached the other end, the molecules at the other end have moved back and forth. Thus energy transfer has taken place (i.e. moving of water molecules). I could use this energy to do some work, (e.g. turn a propeller).
This can also answer the 2nd funny question below
==========================================
Q) In case of Direct current, electrons move in a copper conductor at a speed of only 1/4mm per second. For such a slow speed it will take an electron several minutes to travel a few inches of wire between the battery and the bulb. How come then does the light bulb turn on instantaneously?
---
RP
Funny question - serious answer
Many a times funny questions pose fundamental aspect to be answered and people just dont answer it. Thanks for bringing it up Roger. What I wanted to promote was that every one around "teaches" current wrongly as when charge passes through a conductor. Where as it should be defined as charge passing through a plane in space. Then all things fall right in place.
Thanks for coming in to answer. Water hose analogy is really good in teaching simple, yet relevant concept. In 12th/13th chapter in Resnick-Halliday-Walker the chapter that described current in +2 (excuse me I have long forgot the chapters now :) long time) that was the only book I found that explained it correctly.
Why use AC?
Fahim
Why DC is not used to be supplied to our homes from Electric Power Plant?
Why only AC???
Why DC is not used to be supplied to our homes from Electric Power Plant?
Why only AC???
ANSWER: GPS satellites, starting electronic forum
Fahim
Mr. RP.. i have a suggestion. if your question is not answered in 24 or so hours you should answer it yourself and pose next question...... is dat ok???
---
RP
Good suggestion
Thats a good suggestion. GPS are global positioning system satellites.
They are indeed geo-stationary.
All others open to pose your questions...
---
anil
What is GPS? Are they Ge-stationary?
GPS is abbreviated as Global Positioning System. It is located at a height of 20,000 km from above the earth. Since, there are totally 29 satellites (24 healthy + 3 standby and 2 are unhealthy) across the globe launched by DoD, USA but we are using 24 satellites. These 24 satellites are placed in 6 orbital planes and it uses Earth centred - earth fixed co-ordinate system.
The GPS satellites are not Geo-stationary. These satellites are placed in MEO orbit. To receive GPS signal atleast minimum of 4 satellites view is compulsory to get good accuracy. These satellites uses L-band (L1 and L2 frequencies)
Types of GPS receivers:
(1). Single frequency hand held GPS receiver
(2). Dual frequency GPS receiver.
The GPS satellites are used to find the User position. It gives latitude, longitude and altitude. Main applications include Navigation, Communication and Surveillance.
For more information: ISRO and AAI are planning to launch WAAS (Wide Area Augmentation System) by augmeting GPS satellites with the Ge-stationary satellites.
---
RP
Great info Anil. Thanks for pitching in. In addition to regular geo stationary sats, there are some control satellites that are geostationary in GPS mission.
Mr. RP.. i have a suggestion. if your question is not answered in 24 or so hours you should answer it yourself and pose next question...... is dat ok???
---
RP
Good suggestion
Thats a good suggestion. GPS are global positioning system satellites.
They are indeed geo-stationary.
All others open to pose your questions...
---
anil
What is GPS? Are they Ge-stationary?
GPS is abbreviated as Global Positioning System. It is located at a height of 20,000 km from above the earth. Since, there are totally 29 satellites (24 healthy + 3 standby and 2 are unhealthy) across the globe launched by DoD, USA but we are using 24 satellites. These 24 satellites are placed in 6 orbital planes and it uses Earth centred - earth fixed co-ordinate system.
The GPS satellites are not Geo-stationary. These satellites are placed in MEO orbit. To receive GPS signal atleast minimum of 4 satellites view is compulsory to get good accuracy. These satellites uses L-band (L1 and L2 frequencies)
Types of GPS receivers:
(1). Single frequency hand held GPS receiver
(2). Dual frequency GPS receiver.
The GPS satellites are used to find the User position. It gives latitude, longitude and altitude. Main applications include Navigation, Communication and Surveillance.
For more information: ISRO and AAI are planning to launch WAAS (Wide Area Augmentation System) by augmeting GPS satellites with the Ge-stationary satellites.
---
RP
Great info Anil. Thanks for pitching in. In addition to regular geo stationary sats, there are some control satellites that are geostationary in GPS mission.
Electronic Forum
The following pages contain questions and answers related to electronics, communication and related disciplines.
Q.) GPS satellites, starting electronic forum
Answer
Q.) Why use AC?
Answer
Q.) A/D Converter, help
Answer
Q.) 8085 Microprocessor Problem, & Multivibrator
Answer
Q.) Diode, Zener Diode
Answer
Q.) Electron Mobility, Electron Mass
Answer
Q.) Super Heterodyne Receiver, Nomenclature
Answer
Q.) Satellite, Shape of Satellite Antennas
Answer
555 IC
Gilbert Cell Multiplier
Signal Strength near oceans
Antenna Design
Displacement Current
RF ID Project Help
MORE COMMING SOON.......
Q.) GPS satellites, starting electronic forum
Answer
Q.) Why use AC?
Answer
Q.) A/D Converter, help
Answer
Q.) 8085 Microprocessor Problem, & Multivibrator
Answer
Q.) Diode, Zener Diode
Answer
Q.) Electron Mobility, Electron Mass
Answer
Q.) Super Heterodyne Receiver, Nomenclature
Answer
Q.) Satellite, Shape of Satellite Antennas
Answer
555 IC
Gilbert Cell Multiplier
Signal Strength near oceans
Antenna Design
Displacement Current
RF ID Project Help
MORE COMMING SOON.......
GPS satellites, starting electronic forum,
RP (7/9/07)
GPS
There was a quiz here that I learn was benefiting a lot of us... Quiz was helping in a lot of ways to many folks by not being just a quiz but more of a forum, I am taking the previledge to start it again...
Lets not call it a quiz. Lets call it a forum, and same rules, you post a question anyone an pour in to answer. Lets see... Here's the first question to trigger the chain reaction :)
What are the GPS satellites? Are they geo-stationary?
GPS
There was a quiz here that I learn was benefiting a lot of us... Quiz was helping in a lot of ways to many folks by not being just a quiz but more of a forum, I am taking the previledge to start it again...
Lets not call it a quiz. Lets call it a forum, and same rules, you post a question anyone an pour in to answer. Lets see... Here's the first question to trigger the chain reaction :)
What are the GPS satellites? Are they geo-stationary?
Subscribe to:
Posts (Atom)
