Questions tagged [antenna-theory]

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

Filter by
Sorted by
Tagged with
2 votes
4 answers
103 views

Is an off-center fed dipole (and/or doublet) inherently unbalanced?

Does a balun/choke have to "work harder" in an off-center fed dipole than when the feedpoint is at the center? Or do the standing waves that develop keep the antenna balanced electrically ...
user avatar
2 votes
3 answers
81 views

Why does an HF "monopole" need dozens and dozens of radials while a VHF/UHF "ground plane" antenna only needs four?

It's a bit counter-intuitive that for an HF vertical antenna (such as a quarter wave monopole) the best advice is to put as many radials and as close to the proper length as possible. The typical VHF/...
user avatar
0 votes
3 answers
85 views

ELF antenna receiver build instructions?

I built a vlf receiver in the nineties but good grief, that's a long time ago and have looked very little at receivers since. I'm interested in frequencies from 12 - 18 Hz. Looking at the following ...
user avatar
  • 101
9 votes
2 answers
2k views

Why are longer antennas not suitable to pick higher frequencies?

I know that the length of an antenna depends on the wavelength of the frequency it's trying to receive. A higher frequency needs a shorter antenna and vice versa. I can see that with a high frequency ...
user avatar
  • 203
1 vote
2 answers
94 views

Small shortwave (20MHz) directional antenna design

I'm trying to do some basic radio astronomy experiments, and I'm currently working on picking up radio bursts from Jupiter. These are emitted at around 20MHz; for all intents and purposes, Jupiter is ...
user avatar
  • 111
3 votes
4 answers
80 views

Is it worse to use an antenna tuner on an already-loaded short monopole?

If I had a good transmatch and wanted to use a spare CB antenna on the amateur HF bands, would I be better off bypassing its tuning coil completely? One ham pastime is using an antenna tuner to match ...
user avatar
0 votes
2 answers
96 views

Can fanned/parallel endfed antennas be used to get higher gain in some directions?

I have two pieces of antenna wire which are roughly 10 m long, with banana plugs at the ends, which I bring to hang in the trees when operating portable. I also bring a 49:1 unun and hopes that my ...
user avatar
  • 305
5 votes
2 answers
654 views

Is the original satellite dish "ruined" when a slot antenna is cut into it?

A fun vertical antenna can be made by cutting a horizontal slot in a satellite dish, as documented in e.g. http://www.w6nbc.com/articles/2016-3QSTdishslot.pdf and discussed in How does a slot antenna ...
user avatar
1 vote
2 answers
73 views

Measuring actual feedpoint impedance for a given frequency

Background I'm attempting to tune an antenna with my NanoVNAv2. I calibrated it using the included open/short/(50-ohm)load standards by screwing them directly onto the NanoVNA one by one and running ...
user avatar
  • 371
2 votes
1 answer
151 views

How do phased array antennas work when they produce spot beams?

Background In a lot of literature regarding satellite communications with phased arrays, you'd see this kind of image: Conceptually, I get the basic concept of how this works - a bunch of small ...
user avatar
0 votes
0 answers
18 views

Keysight ADS User-Defined Models to AWR/Virtuoso

everyone! In ADS Keysight it is possible to create an item model - the so-called User-Defined Model. This is C++ code that describes the Y-matrix of the component. Is there the same possibility in AWR ...
user avatar
2 votes
4 answers
110 views

What's the methodology of MDF magnetic field antenna?

I get a MDF 9400 magnetic field antenna from school. I am not able to disassemble this flat antenna to take a picture. I am not sure if this antenna detect only magnetic field. I am not sure if ...
user avatar
  • 604
0 votes
3 answers
61 views

Follow Up on a previous question- Transmit antenna on HF band

I had asked a question in a previous segment and the link is provided below Antenna Size limits at 2-30 MHz (10 m to 150 m wavelength) I think i have some more clarity on the question I wanted to ask. ...
user avatar
5 votes
5 answers
292 views

Does an antenna pick up signals of all frequencies or only its resonant frequency?

I heard that an antenna picks up signals of all frequencies, and then these signals are filtered by a circuit using an inductor and capacitor, and that this is how a radio is tuned. However, I also ...
user avatar
0 votes
0 answers
44 views

What is the differece of a large loop antenna and a small loop antenna in terms of their response to an electromagnetic wave?

there is something that I dont get. I read that a small loop Antenna (also called magnetic loop) responses more to the magnetic field than the large loops does. I was wondering why this is the case ...
user avatar
  • 61
6 votes
0 answers
53 views

How does Large Loop Antenna work physically?

I am learning about loop antennas at the moment. I read that the respone of a small loop Antenna is propotional to the rate of change of magnetic flux through the loop which causes a uniform current ...
user avatar
  • 61
3 votes
0 answers
57 views

Turnstile antennas with a "single-point feed": what's the antenna theory behind this, and how do I build/model it?

The conventional turnstile antenna uses a 1/4wl phasing line between the crossed elements, to get the required phase shift. 4nec2 includes an example file, though, of a circularly-polarized Yagi using ...
user avatar
  • 31
6 votes
2 answers
106 views

Power rating of a selfmade air coil

A colleague was winding an air coil himself. It's a 110µH coil with 200 windings for an 80m antenna, intended to be used on a 600 W transceiver. He used a copper lacquer wire with 0.6mm diameter. ...
user avatar
3 votes
1 answer
74 views

Parameters needed to calculate inductor value to achieve proper phase delay?

I'm thinking about trying a coil in my collinear 5/8λ antenna, instead of the 3/8λ phasing delay line between the lower and upper elements pictured below. I figure that a coil with a certain ...
user avatar
2 votes
1 answer
110 views

Coupling Capacitor of an Antenna

I have a simple question about general meaning & importance of the coupling capacitor in following part of a simple receiver circuit: Is it true that the proper reason why this coupling capacitor ...
user avatar
2 votes
3 answers
275 views

radials for 6 band Hustler vertical

I don't have room for quarter length radials for my Hustler 6 band vertical (10through 80 meters). Can I use 20 foot radials? If so, how many? The hustler is a Hustler 6-BTV 6 band HF vertical ...
user avatar
4 votes
5 answers
132 views

Antenna tuner at the transceiver output confusion

I am a bit confused. Let's take a HF transceiver for example. My understanding is that the output impedance of the transmitter is 50 ohms. The impedance of the coaxial cable feedline is 50 ohms, and ...
user avatar
3 votes
1 answer
81 views

Phasing stub length for colinear 5/8λ?

I've been designing a "Super J-Pole" for 10M in MMANA-GAL, but I'm designing it having two 5/8λ sections. However, I came across this picture: Various J-Poles types diagram indicating the ...
user avatar
3 votes
2 answers
85 views

Impedance miss-match short vs long section?

Let's say there is a 50 Ohm transmission line coming from a transmitter, suddenly the transmission line is spliced into a 300 Ohm line. From what I've learned a partial reflection occurs at this point....
user avatar
2 votes
1 answer
62 views

What is the signal of a receptor antenna irradiated with a plane wave?

Lets say there is a reception antenna connected to a detection system with a coax, and a transmitter sends a plane wave. What happens is that the antenna gets a certain power, following the [...
user avatar
-1 votes
1 answer
164 views

Fractal antenna shapes that work for you? [closed]

I just answered this question, and I wanted to know if any particular shape has been found to be successful for anyone. There seems to be a lot of research on IEEE that indicates that there should be ...
user avatar
1 vote
2 answers
166 views

What is the minimum height required for a 60 meter NVIS antenna?

Various answers include 1/8th of the wavelength all the way down to 1/10th, but would 1/15th or even 1/20th of the wavelength be sufficient for a 60 meter (5 MHz) horizontal NVIS antenna?
user avatar
5 votes
2 answers
167 views

Will a HF beam antenna on rooftop building interfere with other antennas there

I am moving into an apartment on the top floor of a building and I intend to install a HF beam antenna for 20 to 10 meters, on the rooftop of the building. I notice that there are already some ...
user avatar
4 votes
2 answers
90 views

Mounting a hex beam on top of a high urban building

I am moving into a new apartment in the city soon which is on the 24th and last floor of an apartment building. I will have access to the roof of the building also. I'm still trying to understand ...
user avatar
3 votes
2 answers
265 views

Mounting a vertical antenna on a fiberglass mast

I have a multiband SE-X80 HF vertical antenna which works ok from 20 meters to 10 meters with a tuner. It is attached to the railings of my apartment balcony at the moment. This is the antenna : https:...
user avatar
0 votes
1 answer
51 views

Is the phase difference between the voltage and current of the standing wave on a dipole antenna constant along the dipole's length?

Everyone knows that a 1/2 λ dipole antenna has on it a standing wave of RF energy the voltage and current of which are about 90° out of phase with each other. The standing wave is circulating reactive ...
user avatar
  • 3,403
0 votes
2 answers
103 views

Why is there so little difference in the gains of Yagi Uda antennas with omnidirectional antennas? Shouldn't the power at the back be at the front?

Consider an omnidirectional antenna with X dBi gain. Intuitively I understand that the power that would have been dispersed in now-dead directions is directed around the antenna. What I don't get is ...
user avatar
3 votes
5 answers
1k views

How do VHF antennas compensate for change in frequency in Frequency Modulation?

I would like to understand how antennas specifically, compensate for variability in the frequency while receiving FM waves in VHF. The way FM works is that the receiver system - receiver and antenna ...
user avatar
  • 169
2 votes
1 answer
101 views

Why don't the traveling waves on a dipole go back down the transmission line?

Why don't the traveling waves on a dipole go back down the transmission line ? Why does the standing wave on a dipole stop at the feed point ?
user avatar
  • 3,403
3 votes
0 answers
59 views

Is this author correct about using a λ/2 of wire for a coil to get the proper delay on a λ/2 collinear antenna?

Is this author correct about using a λ/2 of wire for a coil to get the proper delay on a λ/2 collinear antenna? Improving the Super-J August 5, 2012 by John S. Huggins I agree with him that there has ...
user avatar
5 votes
5 answers
785 views

Grounding a vertical antenna from a balcony

I have a multiband vertical antenna mounted onto the railings of my balcony apartment high up on the 6th floor of an apartment building. The antenna is not grounded. This antenna comes without radials....
user avatar
7 votes
5 answers
2k views

Why are an antenna’s nulls sharper than its lobes?

Why, for realistic directional antennas, are its nulls sharper (deeper, narrower, etc.), than the radiation pattern’s lobes (local angular maxima)? Is there some physics or mathematical geometry to ...
user avatar
  • 12.4k
5 votes
2 answers
342 views

Can coax be run through the center of a radiating element without currents being induced on the coax shield?

I run a λ/2 vertical dipole for 20M that's fed to a 1.5:1 balun at its center with coax that is perpendicular to the dipole (parallel to the ground), for about 30 feet before it comes down to the ...
user avatar
0 votes
3 answers
227 views

Does anyone know of a compact ELF wave transmit antenna I can buy or make?

I need to transmit frequencies as low as 1Hz and I know the wavelength is the speed of light but wondered if there has been any breakthroughs in this field? I need a handheld antenna or at least one ...
user avatar
2 votes
4 answers
426 views

I'm looking for an effective beam antenna for both 20 meters and 10 meters

My favorite HF bands are 20 meters and 10 meters. I am currently using a multiband vertical antenna, but really it's not so great for DX'ing. I am looking for a good upgrade. I'm still learning alot ...
user avatar
1 vote
2 answers
165 views

Is there such thing as a center-fed longwire?

I want to make a longwire/Beverage receive antenna that will work on a wide range of bands (80-10m or wider). I've got a place where I can put a wire of at least 50m/150'. The only problem is — the ...
user avatar
  • 291
0 votes
1 answer
69 views

How to Measure Bandwidth using just your receiver [closed]

How do you measure the two to one bandwidth of an antenna using a Bird Watt meter? Tom Planer KJ9P
user avatar
5 votes
1 answer
272 views

Why are loopstick ferrite antennas commonly wound with Litz wire?

What is the advantage of using Litz wire to wind ferrite (loopstick) antennas? How much of an advantage in what characteristic does this type of wire provide? (over generic single strand enameled or ...
user avatar
  • 12.4k
2 votes
2 answers
94 views

How to compute the efficency of an omnidirectional antenna from its gain?

Some antennas have very limited specifications with no stated efficiency. For example, this antenna has the following specifications: Frequency Band 902-928 MHz VSWR <2.0:1 Impedance 50 Ω Gain ...
user avatar
  • 165
-1 votes
4 answers
174 views

What comes first, Voltage or Current?

Impedance can be defined as cause / effect or Z = E / I. This means that a difference in voltage potential causes a flow of current, the rate of current flow depending on the impedance. In a dipole ...
user avatar
  • 3,403
1 vote
2 answers
271 views

For a resonant half wave dipole, is the phase of the applied RF voltage at the feedpoint in phase with the current reflected from the ends?

For a resonant half wave dipole, the voltage and current of the standing waves on the antenna are 90 degrees out of phase with each other. At resonance, is the phase of the current reflected back from ...
user avatar
  • 3,403
1 vote
3 answers
174 views

Aren't all antennas technically dipoles?

Since all antennas require a ground, reference or otherwise, there are two poles for their operation. For a mag mount, the car body is the reference ground. A vertical cannot operate without a ground ...
user avatar
2 votes
0 answers
45 views

How might various conductive mast mounting configurations affect an electrically isolated rhombic antenna?

Assuming a rhombic antenna is: terminated for directionality electrically isolated at its mount point mounted to a metal mast partway up vs top of mast horizontally oriented (elements parallel to ...
user avatar
3 votes
1 answer
55 views

Impedance of V Antenna as Function of Angle

I'm trying to experimentally investigate the radiation resistance of a v-shaped antenna. When it's fully unfolded and the reactance is at resonance, the resistance is about 73Ω. When it's folded, it ...
user avatar
3 votes
4 answers
291 views

Is a resonant antenna inherently more efficient because it couples to free space more efficiently?

I saw an interesting assertion recently, that resonant antennas are more efficient because they provide a better impedance match to free space at the resonant frequency. I believe that to be untrue, ...
user avatar
  • 8,922

1
2 3 4 5
9