Questions tagged [antenna-theory]

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

Filter by
Sorted by
Tagged with
3
votes
2answers
134 views

What kind of loop antenna is this, and what is the relationship between its diameter and wavelength?

At the bottom of webpages in the advertisement swamps I keep seeing this image of an antenna, accompanied by an offer that I won't be clicking on. But the antenna itself looks quite intriguing. It's ...
3
votes
4answers
338 views

Give vertical antenna directional gain?

So here is a strange thought. If a vertical electrically speaking is a half dipole with the other half as a ground plane to balance out. Perhaps there are ways to make equivalent director and ...
3
votes
4answers
207 views

What is the voltage on a half wave dipole measured with respect to?

As I understand, voltage is a measure of the potential difference between two points, and voltage causes current to flow. I see lots of descriptions on how dipoles work with lots of references to the ...
3
votes
5answers
571 views

Gain difference between half-wave and infinitesimal dipole?

In discussion around another Q&A here, Glenn W9IQ commented: The directive gain difference between a half wavelength dipole and an infinitesimal dipole is only 0.39 dB I'm curious where this ...
3
votes
4answers
167 views

How does the thickness of the radiator affect an antenna

Another question (Metal for antenna construction?) covered some aspected of this question, but the answers didn't exactly answer it, so I'll make it specific. Given 2 dipole antennas, resonant at the ...
3
votes
3answers
837 views

How thick should counterpoise wires be?

I would like to use a shortened whip antenna with a coil in it's base, e.g. OPEK HVT-400B. My transceiver maximum power is 100 W (and antenna's - 120 W). To make the antenna work I need counterpoise ...
3
votes
3answers
592 views

Why does an “electrically small” antenna have narrow bandwidth?

Reading this interesting piece on magnetic loop antennas, the author explains that a magnetic loop has great efficiency even at small size, but the the price you pay is very narrow bandwidth. Why is ...
3
votes
4answers
133 views

Is there a way to explain antenna radiation patterns on receive without reciprocity?

I don't consider myself an expert, but I have a fairly decent understanding of radio. I belong to a club that includes a number of people who have less theoretical background. I understand that ...
3
votes
3answers
515 views

What happens to a vertical Yagi when you mount it on a vertical metal pole?

How much difference does a metal pole make when it's sitting in the middle of all the lower elements of my beautiful new highly optimized to the max YO.EXE 10 m yagi ? I get it that the closeness of ...
3
votes
2answers
765 views

How low can a vertical dipole be mounted?

An answer to this question suggests that raising a vertical dipole sufficiently can create the effect of a phased array. How about the opposite. How low can a vertical dipole be mounted? Can a ...
3
votes
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 ...
3
votes
3answers
637 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 ...
3
votes
2answers
6k 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 ...
3
votes
2answers
10k views

Spacing between elements on a Yagi antenna

Does anyone know what the spacing between elements on a beam antenna should be? I built a 146 MHz 3 element beam following instructions, and the spacing was 16" between the driven element and the ...
3
votes
1answer
462 views

What is the turn spacing on a Helix Antenna?

I want to do some satellite communication so I thought why not build my own helix antenna. I found this page: Helix antenna design and construction details The most things are clear except for the ...
3
votes
2answers
141 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\...
3
votes
1answer
140 views

How do I design a dual band LPDA antenna?

Im not sure if this is the best place to ask a question like this but its the best place i could find. My goal is to build a dual band antenna similar to this one. That covers ...
3
votes
1answer
110 views

Electrical Earth

I have moved to a new flat which is on the 4 floor, luckily the landlord has let me put an OCF dipole outside with coax feeding through an existing hole in the window frame. I'm looking for some ...
3
votes
1answer
72 views

Antenna Patterns and Multipath Effect

It's said that in order to decrease multi-path effects on receiving antennas that your antenna pattern should have a sharp slope near the horizon. Why? for example this is article mentioned it.(...
3
votes
2answers
296 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.
3
votes
2answers
473 views

Antenna gain vs. radiation efficiency in 4nec2

I'm trying to evaluate HF antennas for low angle performance to pick from a list of designs that will fit in my limited space. I'm using 4nec2 to simulate them and compare the patterns. When your ...
3
votes
3answers
4k views

How to produce a NEC antenna file (and what software to use it with)?

So I'm really trying to get to grips with antenna radiation patterns, and more importantly things that are to close to the antenna that might interfere. I've downloaded Qantenna and 4NEC2 to try and ...
3
votes
2answers
311 views

How do I listen to the amateur radio satellites?

I'm new to amateur radio, and I would like to listen to those satellites in the orbit. Where do I start? What types of amateur radio satellites exist?
3
votes
2answers
251 views

Will wrapping an antenna around my house next to metal affect it?

My unit is 25' by 25' each side and the front is 22' across. The overhang is about one foot with aluminum and vinyl underneath. If I wrap an OCF dipole (fed with 4:1 balun) around this overhang in ...
3
votes
1answer
532 views

Twisting copper wire for a less-flexible DIY antenna

I am making DIY antenna for a home project. The antenna is going to be "V-dipole" with leg length about 53cm. Unfortunately, I didn't find a thick copper wire, but I have a lot of thin core from tv ...
3
votes
1answer
318 views

Understanding of NFC Reader Antenna matching

I have been designing a 20 x 20 cm square NFC reader antenna which looks like this: In order to make it work and detect NFC tags at certain distance, it needs to be matched. To do that I was trying ...
3
votes
1answer
389 views

Is a J-pole an appropriate antenna for mounting to a steel handrail?

Last year, a group of us placed a battery-powered 2m digipeater using a J-pole antenna on a mountaintop. We're planning on doing the same this year except we plan to use a surge arrestor from the feed ...
3
votes
1answer
385 views

Dipole Center Spacing

I have a question about dipole construction. I am working with a turnstile, but building dipoles to validate my system with linearly polarized transmission before moving on to circular. My design has ...
3
votes
1answer
242 views

Is it possible to make a shield that blocks time-varying electric fields, but not time-varying magnetic fields?

Take, for example, a shielded loop antenna. It is often claimed that the antenna is inside the shield, and the shield blocks electric fields from reaching the antenna, while allowing magnetic fields ...
3
votes
1answer
369 views

Microstrip Loop Antenna Design

I am trying to design a loop antenna for operation at 2.4 GHz, I would like for it to have above 2.5 dB gain at 2.4 GHz and have relatively good return loss (<-10 dB). I have started my design as ...
3
votes
3answers
2k views

Using inner conductor of a coax feedline as an antenna

Can I use the inside conductor of coax to radiate RF energy? My in-laws have some sort of attic antenna installed many years ago for broadcast reception, which I would love to temporarily co-opt for ...
3
votes
2answers
1k views

Is it possible to calculate the Q factor for an antenna type, given a frequency?

With only pen and paper, is it possible to calculate the ideal Q-factor for e.g. a dipole antenna, loop etc, given a frequency?
3
votes
1answer
85 views

How much distortion would aluminium wire stays for the centre-pole on my inverted-vee cause?

I used nylon rope from the nearest hardware store to stay the centre-mast on my inverted-vee for the 20. The centre-pole is a long long looong bamboo. The trouble is rain here really isn't friendly to ...
3
votes
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, ...
3
votes
2answers
947 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, ...
3
votes
3answers
164 views

Antenna proximity limit to increasing signal strength via additional receiving antennas?

I have a 900Mhz transmitting antenna that is being received by one receiving antenna at the moment. I want to add a second (and possibly third, fourth, etc) antenna to increase the signal strength. ...
3
votes
1answer
91 views

What type of antenna is this?

I have very little knowledge about antennas (I just read about simple dipoles and monopoles recently) and I need to buy a directional antenna for my wireless device. I have found a cheap antenna (I ...
3
votes
0answers
44 views

How to simulate two antennas in 4nec2

I need to simulate 2 helix antennae placed side by side, and see the resultant radiation pattern. But after adding the second antenna with a separate and when I try to simulate 4nec2, only simulated ...
2
votes
3answers
309 views

Do PCB antennas suit for NOAA and ADS-B?

I saw many designs for creating DIY antennas for NOAA (~137MHz) and ADS-B (~1090MHz) but never seen it in a PCB implementation. So I have a rookie question: why nobody uses PCB antennas for such ...
2
votes
3answers
324 views

Why long wire antenna length shouldn't be a multiple of λ/2?

Numerous sources say that LW length shouldn't be a multiple of λ/2 for any frequency in interest. This will cause the antenna to have a high impedance at this frequency. Since the coax cable impedance ...
2
votes
2answers
130 views

Will using a 1:1 balun at the feedpoint of a center feed dipole result in no common mode current on the outside of the coax?

Will using a 1:1 balun at the feedpoint of a center-fed dipole when using coax result in no common mode current on the outside of the coax ?
2
votes
3answers
120 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 ...
2
votes
2answers
262 views

Fan dipole radiation pattern

I'm looking at dual band (2 m & 70 cm) antenna designs for my next project. A very interesting one to me is the Mighty Woof, which is essentially a fan dipole made of copper pipe. Would the ...
2
votes
2answers
131 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?
2
votes
2answers
148 views

Is an antenna resonant at the frequency of lowest impedance?

I understand that an antenna is resonant at the frequency where the capacitive and inductive reactance cancel out to 0. Only the resistive impedance remains at resonance. Does this mean that the ...
2
votes
3answers
108 views

Why is self-resonance important in a loop antenna?

I visited a "small loop antenna" calculator web site today and fed in my horizontal loop gepmetry, curious to see what it would say. 2" dia wire, 72' circumference, 3.935MHz. Interesting results, ...
2
votes
5answers
528 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
votes
2answers
649 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 ...
2
votes
2answers
1k views

Hentenna beam…is it possible?

I did a (Amateur Radio) search for 'hentenna' and got not one hit. So, to boldly go where no man has gone before, I want to explore the strange new world of creating a beam antenna with Hentenna DE, ...
2
votes
3answers
142 views

Add capacitor to unload antenna?

So add inductor coil(loading coil) is to cancel out capacitive reactance to make the antenna electrically longer. But what if a capacitor is placed on the antenna, to make the antenna electrically ...