Antennas Definition and 95 Threads

I'm currently preparing for a challenge exam, and I'm having trouble understanding antennas. My physics book is good, but it is very brief in its section on antennas. I know there are more complicated types of antennas, but let's just stick with the "simple" half-wave antenna (or dipole antenna...

Its been a while since I studied physics, so pardon my ignorance. I have two near field antennas (NFC). The range of the antennas is about 2-3 cm. I am looking for a way where I can block and unblock the communication between them. One of the way that I tried is to place a flat tightly...

Seems to me in that an antenna is carrying microamps at most that slightly higher resistance of steel Vs copper wouldn't matter. What's the fault of this logic??

Hi pf, I thought that current will flow in closed loops only , but the figure attached shows working of antenna with current in open circuit, but how? :confused: -Devanand T

I grew up not far from WLW and it's giant diamond antenna mast. picture These Blaw-Knox antennas were extremely popular in the 1930s. I always wondered why the diamond shape. I found the original patent here, but it really doesn't say specifically why the diamond shape was chosen. It looks like...

Antenna is in size of 0.5[m] X 0.5[m], with transmit frequency of 10GHz. In a distance of 100m the electric field is 250 [V/m]. I calculated the density of power with the formula: 0.5*(E^2)/(120*pi) and got: 82.891 [W/m^2]. the question is: can I calculate the density of power again but un...

I have some conceptual questions regarding capacitors and dipole antennas. Consider a parallel plate capacitor made with two conducting plates, initially uncharged. If I connect each plate to a different terminal of the battery, charge will start to flow from one plate to another. Consider...

Yer.. I'm lazy and tired, did not enough research and found out that the radio/electromagnetic wave makes all the electrons move back and forth when the wave oscillates between the magnetic and electric fields... so you can see how much the current oscillates etc. But... um cameras work...

The greater the amplitude of a given frequency of light hitting an antenna the greater the induced speed of electricity in the antenna? Reply in simple english please.

My question is just what the title says. Why is copper tubing used instead of normal wire or enameled wire to make antennas and coils at high frequencies? Does it offer less resistance than normal wire?

How can you find the resonant frequency of an antenna whether it is a rod shape or an irregular shape or a sphere? I understand they have a capacitive reactance and you may need an inductive load but can someone explain it all in detail and include which formulas to use. I have a radio antenna...

Hi, So I was thinking, if you've got a metal rod of random size, then any EMR wavelength that the rod (antenna) is a similar length to will stimulate an AC current inside the rod as a complete mess. (It would be the sum of all the frequencies the rod can resonate with) IS THIS ACCURATE?? But...

Homework Statement Two radio antennas radiating in phase are located at points A and B, 200m apart. The radio waves have a frequency of 5.80MHz. A radio receiver is moved out from point B along a line perpendicular to the line connecting A and B. At what distances from B will there be...

I just saw one of these antennas, and I'm puzzled a bit by it. Why would one choose to use a parabolic wire antenna instead of a solid parabolic antenna? It would seem to be much less efficient at first glance (although I don't know if it is true or not). And how do the wire elements manage...

Homework Statement An electric dipole antenna used to transmit radio waves is oriented vertically. At a point due north of the transmitter, how should a second electric dipole antenna be oriented to serve as a reciever? Homework Equations Im not sure if my answer below makes sense, is...

hi, I know that a GPS receiver module receives a number of signals coming from GPS satellites and the receiver can distinguish between them based on a number 1-32. Is there a limit to the number of signal one can send on a specific carrier frequency? Is there a limit to the number of signals...

Why is so much emphasis placed on matching the impedance of a feed line with an antenna? Shouldn't the emphasis be placed on matching the internal generator impedance AND feed line with the antenna instead? That is, you take the impedance of the source, transform it using the transmission...

Anyone have suggestion on other forums that are more into antenna theory and design?

Hi everyone, Light has a dual nature ; wave and particle. Particle part can be explained using Quantum approaches while the wave nature is described by Maxwell Equations. I am interested in light - matter interactions from wave approach which is also my thesis subject. (also I would like to...

Dear all, I am trying to understand what is the difference between a transmitter and receiver antenna. If I recall correctly an antenna is a dipole so you can always use it to either transmit or either receive. All the antennas that are used for transmitting purposes come with some...

HI, I am using tx433/Rx433 RF modules to transfer some data between two AVRs. I know that we have to use 30-35 cm simple wires as antennas. I send out out two bytes. The second byte is the actual data , and first byte is to get rid of unwanted information. However, I have a hard time...

Greetings, As much as I know about science, sometimes something very fundamental dawns on me that I do not understand. I thought all photons were emitted by electrons. Having recently been pursuing interest in radio communication, I realized I do not understand how an antenna produces a...

If you've used Apple's latest iPods, you know that they feature a built-in radio that uses the headphones themselves as an antenna. But how is this possible? I really have two questions about this: 1.) Aren't the headphone wires shielded and insulated so that they should not be able to...

Hey all, currently I am working on a project, which uses the principle of superposition of two antennas. I placed two antennas on the plane and make sure that they are oriented identically. The distance between these two antennas is around 51cm. I did an experiment, in which I firstly get the...

I don't know much about antennas, but I've seen descriptions of the field around dipole antennas that make a difference between the "near field" and the "far field", where the far field is more or less a pure radiation field of photons traveling away from the source, and the near field more like...

Homework Statement In terrestrial microwave link, line-of-sight transmission limits the separation of transmitters and receivers to about 40km. If a 100mW transmitter at 4GHz is used with transmitting and receiving antennas of 0.5m^2 effective area, what is the received power level in dBm...

[SIZE="3"]...residual signals of CMB radiation from the Big Bang? I've heard and read this before but I'm not too sure how credible this is. Are TV antennas really that strong to pick up CMB?:confused: Just wana get this cleared up by an expert. Thanks.

hi, need some help answering some antenna questions... 2 isotropic radiators at x = -d and x = +d on the horizontal x-y plane. for primary radiation lobes to be in +/- y directions, the radiators are fed by 100Mhz sources having equal amplitudes with no phase difference. 1) a strong...

Homework Statement Two antennas located at points A and B are broadcasting radio waves of frequency 96.0 MHz, perfectly in phase with each other. The two antennas are separated by a distance d=12.40m. An observer, P, is located on the x axis, a distance x=55.0m from antenna A, so that APB...

Hey, I'm looking for the optimal antenna to transmit in the 900 Mhz range from a high altitude balloon. The transceiver I have says it is capable of 40 miles LOS with a 15 dBi antenna. Can achieve this? Can I just hang say a 100ft wire from the bottom of the balloon? Do I need a different...

Homework Statement This problem has even stumped my Physics tutor. "Explain why TV receiver arrays in densely populated areas (eg, Western Europe) have both horizontal and vertical antennas." Homework Equations N/a The Attempt at a Solution Unable to find any information on...

I have started working on trying to design some better antennas for the cave radios in use for radiolocation and general caver communications. Most of the antennas I have seen are loop antennas operating at 65 or 130-ish kHz. I am open to all sorts of antennas. Of course no matter what...

I have a lot of general questions on the design of RF antennas. Where do the geometries come from? I've been looking at embedded PCB antennas and also modules that attach to PCBs and they always have exotic looking notches and curves. Some are 3D while others are flat 2D styles. How does...

Why is it that very low frequency signals cannot be transmitted by antennas? (Or why is it inefficient?) Thanks!

Hi. I am designing an experiment focused on radio waves for my experiment and this is the basis of it: Three antenna's will be tested for point to point transmission (VHF): [ 144 MHz ] >>3/4 Wave antenna >>1/4 Wave antenna >>5/8 Antenna (Best Angle of Radiation Usually) These...

Hello All, I have a question related to the understanding of how an active antenna works. From my *extremely limited* knowledge of the subject, I hear that an active antenna is able to receive a stronger signal from a transmitting source by transmitting a wave of the same frequency such that...

Homework Statement I am trying to understand how the total directivity of an array of antennas is calculated. Homework Equations 1. A_e = (D * lambda^2)/(4 * pi) where: A_e = effective aperature (or area of antenna) D = Directivity of one antenna lambda = wavelength 2. D_t =...

Dear PF members , I need you help. I am offered to work on a project at a University. The offered project is microwave antenna design. I asked for some topics to study to keep me updated and ready to work on the project from day one and the professor gave me these : small antennas, planar...

1. Consider N similar antennas emitting linearly polarized electromagnetic radiation of wavelength \lambda and velocity c. The antennas are located along the x-axis at a separation \lambda form each other. An observer is located on the x-axis at a great distance from the antennas. When a single...

Hi to everyone. I have heard that we usually prefer to modulate signals at high frequencies so the wave length is small compared to the length of the antenna. Is there any rule or equation that implies this requirement?

Hi i need information about th dbi and dbd... I know what db is but i am trying to understand dbi and dbd... Also i want to know what if the antennas or the tvs antennas has some gain.. I know that the gain refers to the antennas surface... that's why the satellite antennas have a big surface...

Hi. Yesterday i have had a strange question.. why can't we use squared pulses in antennas? What kind of pulse can we use in antennas? Thx a lot

Does reciprocity, the rule that electrical specifications of an antenna are essentially the same for receiving and transmitting [Wikipedia], apply to the following situation: Antenna Y transmits with power PY which antenna Z receives as power PZ. Does this mean if that antenna Z...

I just need a little direction to get started on this problem. A magnetic dipole is uded to detect an electromagnetic wave. The antenna is a coil of 50 turns with radius 5.0 cm. The EM wave has frequency 870 kHz, electric field amplitude 0.50 V/m, and magnetic field amplitude 1.7 x 10^-9...

Hi, I have a question relating to RFID antennas... For inductively coupled RFID systems, the max. range is about 1.4 times the diameter of the sender antenna (for a loop antenna). In low frequency systems (125, 134 kHz) the antenna coil is often wounded around a ferrite rod, making the...