Questions tagged [antenna-theory]

Designing antennas, selecting antennas for specific applications, properties of a given antenna design.

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3
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2answers
283 views

What is the easiest way to eliminate a beam antenna's backward radiation (rear lobe)?

I tried a metallic reflector which works well in terms of radiation, but considerably degrades the return loss and adds more complexity to the design.
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1answer
402 views

Gain in long wire antennas

DARA (you know, Hamvention) TNG is looking for projects. Thursday, I will be proposing building and characterizing a vertically-polarized 1 wavelength on a side reentrant rhombic. Since in doing the ...
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1answer
545 views

SDR - discone antenna setup

Here's a picture of my SDR receiver setup... This entire setup lives indoors as I'm not able to put anything up on the roof right now. My understanding of a discone antenna is that the downward ...
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1answer
1k views

Designing VLF antenna

I was doing some research about the relation between wavelength and antenna size and shape. I was mostly interested in 15KHz rf range. Based on my research I found the following: A squarish shape ...
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2answers
150 views

Physics behind this decametric radio telescope

I am following this design for a simple decametric radio telescope. I understand the principle that a radio wave hits the metal inducing an electric current that can be measured, but I do not ...
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3answers
140 views

Which antenna would you use?

I'm starting to study RF propagation at college, and I'm thinking about what antenna I should choose for this scenario: The distance between the transmitter and receiver is just 700 meters, and the ...
3
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2answers
140 views

Can you create a radio beam with a Faraday cage?

Imagine we have an isotropic antenna at the origin emitting a steady sine wave at frequency $f$. Encompassing the antenna is a sphere of radius $r$ made of a fine copper mesh (with holes $\ll\frac\...
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5answers
6k views

Aluminum vs copper antenna element lengths

Does the particular metal used in antenna elements make any difference in element length or spacing, i.e. 1/2" aluminum tube vs 1/2" copper tube? I know that length and diameter have an effect on ...
2
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3answers
119 views

Could 8' Marine whip antennas operate on much higher frequencies?

I have backgrounds on electrical communications, but know little about EM/RF. I would like to install outdoor antennas for experiments (receive only; I do not hold licenses, although I do intend to ...
4
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3answers
359 views

Radials on a vertical, spread out evenly or not?

To have a groundmounted quarter wave vertical with a decent efficiency you need at least 16 radials. So normally you would spread them out on the ground evenly around the base. This would give an ...
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3answers
395 views

Total cancellation in corporate feed network for patch antenna

I'm trying to build an array of patch antennas in order to receive a GPS signal. The idea is to build 4 patches and connect them with a corporate feed network. An example of corporate feed is this one....
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3answers
2k views

Feeding a dual-band UHF and VHF Yagi antenna

I just built a UHF Yagi antenna for my HT, and I was thinking about adding VHF elements. If I do, could I just connect the coax directly to both sets of elements without a diplexer?
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3answers
249 views

Would the antenna described work?

For reception of amateur radio satellites, turnstile antennas (consisting of two crossed dipoles fed out-of-phase) are often used. I've recently had an idea - what if two half-wavelength dipoles are ...
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2answers
583 views

Do the radials of a quarter or 5/8 wavelength antennas connect to the braid of the coaxial cable?

I'm studying for my foundation license (in the UK) and I have these diagrams: Do the radials in a quarter or 5/8 wavelength antennas connect to the braid/shield of the coaxial cable? If so, how does ...
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1answer
85 views

Resistance of antenna dipoles

A quick question: Is it a disaster if the two legs of a v-dipole antenna are different resistances? Thanks.
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2answers
2k views

Optimising a small magnetic loop with 1:1 SWR but little radiation

I'm trying to build a small magnetic loop for 5W on at least 40m - 20m following ideas of G4ILO's wonder loop. For this, I'm using coax with a ~2mm copper core and ~1mm spacing to the braid (see 1st ...
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6answers
919 views

Use a TV coax and balun for a poor-man's OCFD?

Can I use TV coax and a cheap TV balun to build a poor-man's OCFD? Marginal performance is acceptable if it saves money. If I could listen to 10% of transmitters within a 100 mile radius that would be ...
2
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5answers
482 views

What happens if an HF dipole is made longer?

Does a longer dipole (than half wavelength), for example twice as long, tuned to 50 Ω using an antenna tuner perform better than a half wavelength dipole for the same frequency?
2
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2answers
414 views

Loop Antenna - configuration?

Due to space limitations, I'm looking at loop antenna designs. I'm starting with receive only, but hope to eventually transmit. I've seen magnetic loops (single turn with a coupled loop) and I'm ...
2
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1answer
309 views

What kind of antenna design is this?

I've found an old antenna that once came with an HP laptop with a TV (DVB-T?) card. I decided to see if I can use that antenna for something else, so I opened it up and found the following antenna ...
2
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1answer
751 views

How do I specify that wires are connected in 4NEC2?

I've been trying to get acquainted with the 4NEC2 antenna modeling program. Perhaps this is obvious, but it's not clear to me that wires with one end in the same place are connected. I'm attempting ...
5
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3answers
639 views

Tiger Tail + capacitive coupling… what's the interaction?

I've been working on a 2m setup for hiking. My goal is to have the best possible antenna that can be used while walking, and that won't get damaged if I walk under a low branch or some other forest ...
4
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3answers
932 views

Colocated three orthogonal wire loops for lightning detection network

I'm considering building multi-turn wire loop receive antennas for a blitzortung.org lightning detection receiver. It has three separate channels for H-field antennas, operating simultaneously. ...
2
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2answers
420 views

Satelite dish modified for Wi-Fi (Signal Elevation Question)

I am doing a project where I will be re-purposing an old TV satellite dish as a directional Wi-Fi antenna. The dish is circular in shape, not oval. The dish has an arm coming from the bottom that ...
2
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2answers
1k views

How much does the quality of coax cable matter?

I am using a bit of coax cable as an antenna (with the shielding off at the last 17.3 cm). However it is cheap Chinese cables and the shielding does not contain that many copper wires (the "web" isn't ...
3
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3answers
609 views

Can 2 uhf beam yagi antennas be used on a transmitter to get a diversity effect?

I'm having a problem getting a good signal up to a repeater site on UHF. I'm running 20W in a neighborhood with lots of trees, and the signal is fading in and out due to trees and the wind. I can't ...
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1answer
2k views

Relation between beamwidth and operating frequency

Radars operating in the X-band have a narrow beamwidth. Radars operating in the S and C bands have a bit more beamwidth than X band radars. I know that antenna size also plays a major role. My doubt ...
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5answers
9k views

When and why does the size of a ground plane or radials matter?

Consider these three cases: My understanding is that when building or installing an antenna designed to operate over a ground plane (e.g. a quarter-wave vertical), the size of the ground plane does ...
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3answers
308 views

Is cheap Chinese coax wire ok to use as an antenna?

So I've been following this guide on how to build an antenna for a High altitude balloon: link In the guide they say to use RG174 wire, which is why I bough some cheap RG174 wire off Ebay. I guessed ...
3
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2answers
815 views

Does a receiving antenna need radials?

I am very new to radio and am using two 433MHz 1/4 wavelength monopole antennas to send and receive data. On the transmitting antenna I'm going to add radials (as it is the standard in my application)...
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2answers
130 views

Antenna experimentation

I want to make a DIY antenna for my Kenwood TH-F6A. Is there any danger of damaging the radio (i.e. by trying an antenna that is unsuitable), or is it safe to experiment?
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2answers
500 views

Linear-Loaded Cage Dipole?

I've recently learned about linear loaded dipoles as one way of building a physically shortened antenna. As I understand it, any shortened antenna will have reduced bandwidth and linear-loaded dipoles ...
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1answer
180 views

Transition Point Between Fan and Cage Dipoles

A fan dipole is a dipole with multiple active elements, either for different frequencies or different directions (see turnstile antenna) while a cage dipole emulates a larger conductive by having ...
2
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2answers
753 views

Optimal antenna orientation for High altitude balloon?

(First of all, I hope this is the right subform, please correct me if I'm wrong) I am using a 433 Mhz LoRa Radio to communicate with a high altitude balloon and am using an antenna like in this guide ...
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2answers
2k views

What is the purpose of having multiple bays for a bowtie antenna?

What would be the difference between a two-bay antenna designed like this: and a four-bay antenna designed like this: Assuming that everything about these two antennas are identical aside from the ...
2
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2answers
622 views

What is output power exactly?

I'm trying to comprehend what one would see if one could observe what's happening in the antenna wire. Is the difference between a 1 watt and a 4 watt transmitter just that the amplitude/voltage on ...
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3answers
1k views

What do you connect antenna Radials to?

I am trying to communicate between two arduino microcontrollers using radio. For this purpose I am building a whip antenna with 4 ¼ wave radials. I've done a bit of reading and have got most of it, ...
2
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2answers
1k views

Field Strength calculations with known antennas

I can receive a calibrated decibel milliwatt signal level from the output of any antenna at a given frequency. With a given antenna gain (dbi) in the direction I want to receive the signal (...
3
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2answers
861 views

Are chokes necessary for VHF and higher frequencies?

I am trying to install a VHF/UHF antenna on my truck, and I have been studying everything I need to do that. I keep reading about chokes, in particular here: http://www.k0bg.com/choke.html However, ...
2
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1answer
676 views

Dual-band rubber duck gain on 2m vs. 70cm

Using a dual band "rubber duck" like the stock Baofeng antenna and/or the physically longer NA-771, which band will give the best results between two mountain tops given the same input power? ...
4
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1answer
410 views

DAB antenna in roof space

We are setting out our roof-space as an attic, and after decorating, there will be a triangular void under the house ridge, which will be about 36" wide, and 18" high. I can easily fit a standard ...
2
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1answer
140 views

Term For Receive Antenna Using Lorentz Force?

Since: $$\vec F = q \left(-\nabla \phi - \frac{\partial \vec A}{\partial t} + \vec v \times \left( \nabla \times \vec A \right) \right)$$ It would seem that a receive antenna with a current density ...
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1answer
418 views

How to assemble an antenna (impedance matching methods)

I got the following plans off Martin E. Meserve's website. How do I go about assembling the antenna once I have the elements and boom? What is the impedance of the driven element? Do I need baluns ...
0
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1answer
53 views

Transmission Line Model of Co-ax Lines

I have got 2 questions on transmission line. In coax line, the centre wire is Copper, and the outer line is Aluminium, as far as I can see in the coax that I have. I have got couple of questions on ...
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3answers
2k views

How does Wi-Fi antenna work?

Since I'm working with wireless communications, I decided it would be good to educate myself a little and at least get a basic understanding how does a Wi-Fi antenna work. My first question is about ...
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2answers
803 views

Dipole Antenna Current Distribution at any Time Instant

Above is a connection of half-wave dipole antenna. The book states that the current profile is same at any given time instant on both the radiators, each of quarter wavelength length. Now my ...
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6answers
6k views

What is the impedance of an end-fed half-wave antenna?

It is my understanding that the feed-point impedance ($Z_a$) of an end-fed half-wave antenna is dependent on at least the following factors: $L_a$: The length of the radiating element of the antenna. ...
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2answers
5k views

How the Coaxial Collinear Antenna Works?

A length of coaxial cable radiates negligible amount of RF. Same length, if cut into pieces of length (λ/2 * VF), and these pieces joined again cross-connected (i.e. core of a piece to shield of ...
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2answers
6k views

How to calculate single-stub match (general case)?

I'm trying to build a 1/2 wave "Coaxial J-Pole" antenna, similar to what is described here: Such an antenna would be great for stringing up in a tree when operating remotely, no tuner needed. The ...
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8answers
7k views

How does the length of a metal sleeve around a (shieled) coax cable affect antenna performance?

A post on http://adsbexchange.com/forums/topic/beginners-2-cantenna-easy-diy-antenna-to-improve-rangeplane-count uses a $\frac{\lambda}{4}$ sleeve made of a pop can beneath a $\frac{\lambda}{4}$ wire ...