Help with Homework???

[armymaj]

The following isn't covered in my book but I guess they still expect me to answer it somehow.... Any help would be greatly appreciated.<br /><br />You are communicating between two satellites. The transmission obeys the free space law. The signal is too weak. Your vendor offers you two options: The vendor can use a higher frequency that is twice the current frequency or can double the effective area of both of the antennas. <br />Which will offer you more received power, or will both offer the same improvement, all other factors remaining equal? <br /><br />How much improvement in the received power do you obtain from the best option?<br /><br />

 

[spacester]

hmmm . . . najaB will know this . . . <br /><br />What's the relationship between frequency and power? <div class="Discussion_UserSignature"> </div>

 

[vogon13]

Remember, I don't do math.<br /><br />-but-<br /><br />I do recall that making antennas bigger isn't 'lossy'.<br /><br />Doubling the frequency is. The hardware, cables, wires, and components all exhibit greater signal losses at a higher frequency.<br /><br />I know what I would do, but if your instructor is angling for a specific angle (those instructors be tricky rascalls, after all) for you to base your answer on, and I didn't sit in on the class, I wouldn't have any way of knowing.<br /><br />Let us know how it turns out no matter what choice you make, its your grade, after all.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[dan_casale]

I'm not sure if this will help or confuse the issue.<br /><br />Wien's law: The wavelength of maximum emmission of a blackbody is inversely proportional to its temperature in kelvins. Thus doubling the frequency doubles the temperature. The formula is (greekletter)=0.0029 K m / T where (greekletter) is the wavelength of maximum emmission of the object (in meters). T = the temperature of the object in Kelvins. m = meters.<br /><br />Next add the Stefan-Boltzmann law for blackbody radiation. This says that if you double the temperature of an object then the energy emmitted from the object's surface each second increases by a factor of 2^4 (16) The formula is F=(sigma)T^4. Where F = energy flux, in Joules per square meter of surface per second. Sigma = a constant = 5.67x10^-8 w m-2 K-4 and T = object's temperature in Kelvins.<br /><br />Anyway, doubling the frequency should give you 16x more energy.<br /><br />Doubling both the receiving and sending antennas, hummmm. I'm not sure of the effect of doubling the sending antenna, unless it will make it more accurate. Doubling the receiving antenna will only help if signal is "spilling" over the side of the antenna. Which kind of "double" the size do you mean from 2'x2' to 4'x4' or 4 square feet to 8 square feet. But the max gain appears to be 4x.<br /><br />This is from the book "UNIVERSE" seventh edition by Roger A. Freedman and William J Kaufmann III copyright 2005 (www.whfreeman.com)

 

[spacefire]

<font color="yellow">free space law</font><br />does that law state that any thread in free space will become a G thread if Jimglen and CrazyEddie are on at the same time? <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[armymaj]

Thanks! This should at least confuse him enough to give me half credit...if I am lucky he will understand it enough to give me full credit. Thanks for giving me the reference also....I better go check it out and try to understand it a little myself. I will let youknow how it turns out!

 

[lampblack]

<font color="yellow">Thanks! This should at least confuse him enough to give me half credit...if I am lucky he will understand it enough to give me full credit. Thanks for giving me the reference also....I better go check it out and try to understand it a little myself. I will let youknow how it turns out! </font><br /><br />So... what kind of grade did you get?<br /><br />I stumbled across this thread just now, and I couldn't help but wonder what would happen if you instructor should happen to hang out in these parts, too. <img src="/images/icons/frown.gif" /> <div class="Discussion_UserSignature"> <font color="#0000ff"><strong>Just tell the truth and let the chips fall...</strong></font> </div>

 

[brandido]

I know this is way too late, but, found the follwoing tutorial on satellite communication. The important part is a formula for the gain of a antenna can be found from the equation <br /><br />G = 4*Pi*A/(w^2)<br /><br />where G is gain, A is the area of the transmitter antenna, and w is the wavelength. However, this does not take into account the gain based on the receiver's antenna. So based on this, the increase in area of the transmitter would result in doubling the gain. Doubling the frequency would half the wavelength, so we get a four-fold increase in the gain. <br /><br />Looking into receiver antennas, I found a discussion of receiver gain From trying to parse this, I get that the gain goes with with the square of the Diameter, or linearly with area. However the gain of the receiver also goes up with the square of the frequency. <br /><br />So, from these two (less than definitive) links, we get that the effect of doubling the area is 2 (from trasmitteR) * 2 (from receiver) = 4. From the doubling the frequency, we get 4 (from the transmitter) * 4 (from the receiver) = 16. <br /><br />So it looks like the winner would be doubling the frequency!