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Wavelength & Distance Relation in MICROWAVE 
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#1
Jul405, 09:05 AM

P: 3

Hey All !
i am basically a computer networks guy, exploring the telecom internals if i am so newbie please forgive me ! my question is that ! Is there any relation between the Wavelength and the distance covered by a MICOR WAVE when radiated through an anteena. Bascially i am confuse, what difference a wavelength make in the tranmisstion of a wave ? like do Higher Wavelength waves need less power to radiate and vice vers. Also what is the maximum range a microwave can travel or it can travell to unlimited distance (increasing the radiation in the area as a drawback ?) . I would be grateful if someone clear this up. regards, Shakeel Ahmad 


#2
Jul405, 10:36 AM

P: 52

Higher frequencies make it easier to transmit. A good example: at the latter part of the 19th century, 2 different companies were fighting to make electricity. One with AC and the other with DC. The company making AC eventually won because the higher frequency makes electrcity travel longer distances without losing power (AC has 60Hz an DC has 0HZ).
Microwaves can travel unlimited distances just like light. They are both electromagnetic waves. The shorter the wavelength, the higher the frequency. Antennas are built taking this into consideration. 


#3
Jul405, 10:55 AM

P: 3

 you said microwaves can travell for unlimited distance ! Practically speaking for transmitting m.w for unlimited or much broader distance , we need to radiate the signal with hight power and it will create much heat and radiation (SAR?) which can be harmfull ?? am i right ?  and, talking about 2.4Ghz Wireless Networks, how can a small wireless card transmitt a powerfull signal to sendback the data to a 1KM far away hotspot. Or a small GSM handset sends data to a 20KM far away Base station. Do they have enough power to transmit the signal to that much distance ?  Is there any formula via we can find out , if we apply that much current to the Microwave, it will cover that much distance.  Talking about Microwave ovens , they work on 2.4 Ghz, so will a 2.4Ghz radio link transmitter possess the same qualities like giving heat bruns etc to a human if touched while transmittion. from above questions i know you can judge how much i am confused. Please if you can clear. regards, Shakeel Ahmad Lahore, Pakistan. 


#4
Jul405, 08:18 PM

Sci Advisor
P: 1,477

Wavelength & Distance Relation in MICROWAVE
I will (try to) answer your questions point by point.
1. Essentially you are correct, to be able to detect a signal further away, we need to increase the radiated power. Also note that the information that can be sent over a channel is fundamentally limited by signal to noise ratio, so increasing the power of our antenna can also (potentially) increase the rate at which information can be sent. Currently, in Australia, the radiation limit from microwave towers is something like 1 mW/cm^2. Most countries have such limits because the long term effects of longwave electromagentic radiation is not well understood. 2. Not my field of expertise, sorry! 3. Radiation patterns vary greatly from antenna to antenna. I don't think there is a general relationship that depends on current only. One would also have to take into account the geometry of the antenna. 4. Whether you get burnt or not depends on the power of the antenna. If the power is sufficiently high (and your hand is sufficiently close), then yes, you will get burnt. Regards, Claude. 


#5
Jul405, 08:38 PM

P: 52

1Yes there are SAR limits. I think the limit is something like 1.6W/KG in the USA. Getting too close to a high Watt transmitter can be very dangerous. I have heard of accidents and people getting seriously hurt.
2Cellphones transmit at 1W of power. More than enough to transmit to about 1020 KM. But that is all they will transmit, nothing more. This is the basis for 'cell phone' technology. Each cell (area in a town or city) is about 10KM in radius. 3Yes there is distinct forumulas to calculate the Power needed to transmit certain distances. The power of the signal decreases by half, for twice the distance travelled. This is an inverse square law. But I don't remember much right now. I will have to open my text books to review. Here is a link with the formulas: https://ewhdbks.mugu.navy.mil/oneway.htm 4 Already answered in 1. 


#6
Jul405, 08:40 PM

PF Gold
P: 7,120

Dont take my word for it, lets see if someone can verify what im talken about. 


#7
Jul405, 10:38 PM

P: 3

I realy appreciate the reply of you all ! it realy helped me to clear the concepts. :)
regards, Shakeel Ahamd Lahore, Pakistan. 


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