View Full Version : Rearranging formula's
Cabdullahi
01142010, 10:11 PM
I just want someone to check if i rearranged this formula correctly
.............Pt.Gt.Gr.lambda^2
Pr =
............16pi^2 d^2
I made Pt the subject because thats what i want to calculate but im getting weird answers..this is how i rearranged the formula to make Pt the subject
Pr.16pi^2.d^2
 = pt
Gt.Gr.lambda^2
Where have i gone wrong?
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Alpha Dude
01142010, 10:23 PM
Pr.16^2.d^2
 = pt
Gt.Gr.lambda^2
Where's pi gone?
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Cabdullahi
01142010, 10:45 PM
sorry pi is there i forgot to write it
also in the second equation the Power received(Pr) is not needed because its 0 when you want to know the power transmitted
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AlHoda
01142010, 10:51 PM
:hiding: i have a headache..... * nightmares*
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Alpha Dude
01142010, 10:55 PM
Originally Posted by
Abdullahii
sorry pi is there i forgot to write it
also in the second equation the Power received(Pr) is not needed because its 0 when you want to know the power transmitted
If Pr is 0, I think your equation would give you 0 for Pt always.
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Nathaniel
01142010, 10:57 PM
Originally Posted by
Abdullahii
I just want someone to check if i rearranged this formula correctly
.............Pt.Gt.Gr.lambda^2
Pr =
............16pi^2 d^2
I made Pt the subject because thats what i want to calculate but im getting weird answers..this is how i rearranged the formula to make Pt the subject
Pr.16pi^2.d^2
 = pt
Gt.Gr.lambda^2
Where have i gone wrong?
You've rearranged it perfectly...so you must have made some other error somewhere in your calculation.
Reply
Cabdullahi
01142010, 11:16 PM
Originally Posted by
Alpha Dude
If Pr is 0, I think your equation would give you 0 for Pt always.
Consider this Pr is unknown but all the other components are known...i want to know what power an antenna will transmit by rearranging the formula Pr .....and Pr at this stage is of no importance only when i find what my antenna is transmitting using the other components will Pr be important for finding what the power i've received
so its 0 and i omitted it from the Pt equation
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Nathaniel
01142010, 11:55 PM
Originally Posted by
Abdullahii
Consider this Pr is unknown but all the other components are known...i want to know what power an antenna will transmit by rearranging the formula Pr .....and Pr at this stage is of no importance only when i find what my antenna is transmitting using the other components will Pr be important for finding what the power i've received
so its 0 and i omitted it from the Pt equation
Setting a parameter to 0 is not the same as saying it's unknown  in fact it's saying that you know its value is 0! Alpha Dude is correct, if you set Pr to 0, Pt will also be 0. If Pr is unknown, then you can only find Pt as a function of Pr.
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Cabdullahi
01142010, 11:59 PM
Originally Posted by
Nathaniel
Setting a parameter to 0 is not the same as saying it's unknown  in fact it's saying that you know its value is 0! Alpha Dude is correct, if you set Pr to 0, Pt will also be 0. If Pr is unknown, then you can only find Pt as a function of Pr.
i made the mistake of thinking that unknown equates to 0 :(
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Nathaniel
01152010, 12:08 AM
Originally Posted by
Abdullahii
i made the mistake of thinking that unknown equates to 0 :(
OK, so if Pr is unknown, you can write down Pt in terms of Pr. Are you being asked to evaluate Pt or just find an expression? If you have to evaluate, perhaps they have given you some more information to help you find Pr, or you can make a good approximation.
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Cabdullahi
01152010, 12:13 AM
Originally Posted by
Nathaniel
OK, so if Pr is unknown, you can write down Pt in terms of Pr. Are you being asked to evaluate Pt or just find an expression? If you have to evaluate, perhaps they have given you some more information to help you find Pr, or you can make a good approximation.
I have to design a yagiuda antenna...i've calculated the gain, wavelength(lambda) and i was given the distance (d)...using lambda i constructed the spacings between the elements on the yagi uda and so by using the Pt formula i want to know what sort of power will i be transmitting using the components given to me already
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Nathaniel
01152010, 12:19 AM
Originally Posted by
Abdullahii
I have to design a yagiuda antenna...i've calculated the gain, wavelength(lambda) and i was given the distance (d)...using lambda i constructed the spacings between the elements on the yagi uda and so by using the Pt formula i want to know what sort of power will i be transmitting using the components given to me already
Can you measure the power received? I'm afraid I know very little about yagiuda antennae... :hmm:
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Cabdullahi
01152010, 12:41 AM
Originally Posted by
Nathaniel
Can you measure the power received? I'm afraid I know very little about yagiuda antennae... :hmm:
if i measure the power transmitted i can calculate the power received...im getting something like
Pt = 1.9378 watts
and for Pr = 1.137 watts
Looking at that my antenna is somewhat efficient but i honestly don't know there is loss but im skeptical about my calculations :(
Reply
Nathaniel
01152010, 01:08 AM
Originally Posted by
Abdullahii
if i measure the power transmitted i can calculate the power received...im getting something like
Pt = 1.9378 watts
and for Pr = 1.137 watts
Looking at that my antenna is somewhat efficient but i honestly don't know there is loss but im skeptical about my calculations :(
What kind of value were you expecting? If it helps, I can go over the calculations you did and check you haven't made a small error somewhere.
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Cabdullahi
01152010, 01:15 AM
Originally Posted by
Nathaniel
What kind of value were you expecting? If it helps, I can go over the calculations you did and check you haven't made a small error somewhere.
thanks sir :)
to find Pt you'll need
these components :
Gt = 11.62* in ration not db
Gr = 11.62* in ration not db
d = 23 meters
lambda = 61
to find Pr you'll need
Pt = You'll get this by doing the Pt calculation
Gt = 11.62* in ration not db
Gr = 11.62* in ration not db
d = 23 meters
lambda = 61
* = 11.62 in ratio is 14.52
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Nathaniel
01152010, 01:27 AM
So to calculate Pr you're doing:
Pr = (1.9378 . 14.52^2 . 61^2)/(16 . pi^2 . 23^2) = 18.1981 (4dp) < much bigger than your answer :hmm:
Is that correct?
Reply
Cabdullahi
01152010, 01:42 AM
Originally Posted by
Nathaniel
So to calculate Pr you're doing:
Pr = (1.9378 . 14.52^2 . 61^2)/(16 . pi^2 . 23^2) = 18.1981 (4dp) < much bigger than your answer :hmm:
Is that correct?
its wayyyy too big i cannot receive more power than i transmitted this never has been achieved in science
try to calculate one component at a time for example write 16 .pi = 50.2 ^2 =2526.61 and note it down somewhere and so on until you get all the component values this way then multipy them just like in the equation and then divide the top by the bottom
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Cabdullahi
01152010, 01:51 AM
this is what i got
Pr = 1520417.374 / 1336581.306 =1.137 ?
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Nathaniel
01152010, 01:58 AM
I get the bottom half of the fraction to be 83536.3317...is the formula meant to be (16.pi)^2 or 16.(pi^2)? I did the latter (which is what your formula implied).
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Cabdullahi
01152010, 02:19 AM
Originally Posted by
Nathaniel
I get the bottom half of the fraction to be 83536.3317...is the formula meant to be (16.pi)^2 or 16.(pi^2)? I did the latter (which is what your formula implied).
in the course notes it says 16π2 i think i made a mistake instead of (16.pi)^2 it should be 16.(pi^2)
i calculated Pt correcting the 16 pi squared issue and i got :
pt = 0.11 watts two d.p
and
pr = 0.10 watts to two d.p
which means my antenna has a loss of 0.01 i think ? which is absolutely sweet...the antenna looks efficient according to the calculations
cheers nathan for clearing things up!!!!! :D:D:D:D:D:D
Reply
Nathaniel
01152010, 02:26 AM
Originally Posted by
Abdullahii
in the course notes it says 16π2 i think i made a mistake instead of (16.pi)^2 it should be 16.(pi^2)
i calculated Pt correcting the 16 pi squared issue and i got :
pt = 0.12 watts two d.p
and
pr = 0.10 watts to two d.p
which means my antenna has a loss of 0.02 which is absolutely sweet...the antenna looks effecient according to the calculations
cheers nathan for clearing things up!!!!! :D:D:D:D:D:D
Ah, that's great! :D Generally 16pi^2 always means 16*(pi^2), and it obviously makes a big difference if you square the 16 too!
Glad it all worked out, I'm always happy to help. :)
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Donia
01152010, 02:54 AM
Wow..
What class is this?
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Donia
01152010, 01:49 PM
I actually was really curious to know which class this was (as evident by me posting again.)
I'm just starting college so.. this is new to me.
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Cabdullahi
01152010, 04:01 PM
Originally Posted by
Donia
I actually was really curious to know which class this was (as evident by me posting again.)
I'm just starting college so.. this is new to me.
sorry for not answering you earlier...this class is the communications and networking class
its do with antenna's, signal propagation,packet switching,IP,radio
all those things :)
again sorry for not answering you the first time
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Misz_Muslimah
01152010, 08:17 PM
Wow mashallah, how do you understand that?
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Cabdullahi
01152010, 08:24 PM
Originally Posted by
Misz_Muslimah
Wow mashallah, how do you understand that?
Its easy sister...but because my maths is a bit rusty im not as good....i've spent more time playing video games than practising maths
you have an antenna like the one above your house those antennas are powered up so that they can send signals to other antennas and there are various calculations that help with this
its just multiplication and division nothing more
thats it really
.................................................. .....
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Misz_Muslimah
01152010, 08:28 PM
^ Sounds complicated :phew
..And I thought Simultaneous Equations was hard! Lol
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Cabdullahi
01152010, 09:22 PM
Originally Posted by
Misz_Muslimah
^ Sounds complicated :phew
..And I thought Simultaneous Equations was hard! Lol
Wallahii i find Simultaneous Equations hard also
Reply
Donia
01152010, 09:34 PM
Originally Posted by
Abdullahii
sorry for not answering you earlier...this class is the communications and networking class
its do with antenna's, signal propagation,packet switching,IP,radio
all those things :)
again sorry for not answering you the first time
There is no need to apologize, brother.
Wow.
I thought it was a science or even a math class. You explained it well.. I do hope I don't have to take it for my major though.
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Cabdullahi
01152010, 09:37 PM
Originally Posted by
Donia
There is no need to apologize, brother.
Wow.
I thought it was a science or even a math class. You explained it well.. I do hope I don't have to take it for my major though.
what major are you interested in
Reply
cat eyes
01152010, 09:50 PM
Originally Posted by
Abdullahii
I just want someone to check if i rearranged this formula correctly
.............Pt.Gt.Gr.lambda^2
Pr =
............16pi^2 d^2
I made Pt the subject because thats what i want to calculate but im getting weird answers..this is how i rearranged the formula to make Pt the subject
Pr.16pi^2.d^2
 = pt
Gt.Gr.lambda^2
Where have i gone wrong?
have you tried using a calculator :><::muslimah:
Reply
Cabdullahi
01152010, 10:00 PM
Originally Posted by
cat eyes
have you tried using a calculator :><::muslimah:
Yes sister i have used a calculator because its impossible to do a calculation like that without one
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Donia
01162010, 03:37 AM
Originally Posted by
Abdullahii
what major are you interested in
Currently Special Education Teacher insha'ALLAH.
Reply
Cabdullahi
01162010, 12:11 PM
Originally Posted by
Donia
Currently Special Education Teacher insha'ALLAH.
Mashallah that's very good teaching students with special needs....you've obviously thought about a career where you could teach and get good deeds pile up in the account for the afterlife
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cat eyes
01162010, 11:20 PM
Originally Posted by
Abdullahii
Yes sister i have used a calculator because its impossible to do a calculation like that without one
i hated maths in school :raging: my teacher use to roar at me for taking long deep breaths of boredom and not paying attention :'(
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Salahudeen
01162010, 11:22 PM
In my math lessons I used to day dream and wake up when the teacher called my name and jus stare at him while he was asking me the answer to some question. lo
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Cabdullahi
01162010, 11:26 PM
i was never good at maths and i still am this way
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cat eyes
01162010, 11:29 PM
Originally Posted by
squiggle
In my math lessons I used to day dream and wake up when the teacher called my name and jus stare at him while he was asking me the answer to some question. lo
but my teacher use to actually make me cryimsad
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Salahudeen
01162010, 11:35 PM
Originally Posted by
cat eyes
but my teacher use to actually make me cryimsad
:raging: you should've thrown paper balls when he had his back turned to write on the board ;D
in my school some 1 stole our teachers keys from his desk, and while he was teaching we saw his car drive past the window and he ran out the class room.;D
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Nathaniel
01162010, 11:55 PM
*Maths teacher walks into the room* :Evil:
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cat eyes
01172010, 12:51 AM
Originally Posted by
squiggle
:raging: you should've thrown paper balls when he had his back turned to write on the board ;D
in my school some 1 stole our teachers keys from his desk, and while he was teaching we saw his car drive past the window and he ran out the class room.;D
:omg:that must have been hell funny ;D i just have a mental picture of it in my head. the thing is when i would get sent to the principles office for being naughty he'd never really say anything just place me in a room and he'd have this geeky orkestra music playing it was bloody torture :enough!:
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cat eyes
01172010, 12:52 AM
Originally Posted by
Nathaniel
*Maths teacher walks into the room* :Evil:
oh sorry sir lol :nervous:
Reply
Salahudeen
01172010, 01:04 AM
Originally Posted by
cat eyes
:omg:that must have been hell funny ;D i just have a mental picture of it in my head. the thing is when i would get sent to the principles office for being naughty he'd never really say anything just place me in a room and he'd have this geeky orkestra music playing it was bloody torture :enough!:
lol it was funny, especially when the teacher quickly ran out the class room lol.
orkestra music lol
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Donia
01172010, 06:43 PM
Originally Posted by
Abdullahii
Mashallah that's very good teaching students with special needs....you've obviously thought about a career where you could teach and get good deeds pile up in the account for the afterlife
I hope so brother. Insha'ALLAH. Plus I also really like children and have an especially soft spot for the disabled.
:sl:
Reply
waqas maqsood
01182010, 02:47 AM
Originally Posted by
Misz_Muslimah
^ Sounds complicated :phew
..And I thought Simultaneous Equations was hard! Lol
I used to hate simultaneous equation in high school.
oh and quadratic equation. Still managed to get an A for GCSE...
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Misz_Muslimah
01202010, 06:40 PM
^ Mashallah, Simultaneous Equations takes a long time to get used to and it's longgg..:phew :exhausted
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