Questions tagged [antenna-theory]

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

Filter by
Sorted by
Tagged with
1
vote
2answers
100 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 ...
5
votes
4answers
97 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....
2
votes
4answers
148 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 ...
3
votes
0answers
45 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 ...
7
votes
5answers
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 ...
-1
votes
0answers
64 views

How does change in dipole angle orientation affects mutual coupling in an antenna array

For dipole antennas in an array system, for any configuration of the dipoles, how does change angle of orientation in one or more of the dipoles affect the mutual coupling between them. Is there a ...
0
votes
3answers
112 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 ...
5
votes
2answers
294 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 ...
1
vote
2answers
88 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 ...
3
votes
1answer
694 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 ...
5
votes
1answer
11k 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 ...
8
votes
3answers
718 views

How would I calculate antenna gain?

The concept of antenna gain is pretty important for calculation of link budget and is something I've had contact with. I know that it tells me how focused the waves emitted by the antenna are and I ...
4
votes
1answer
166 views

How do dual band J poles work?

My understanding is a J pole is a $\frac{1}{2} \lambda$ dipole attached to a $\frac{1}{4} \lambda$ impedance matching element. How does this dual band work? What acts as the impedance matching element ...
0
votes
1answer
57 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
5
votes
1answer
139 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 ...
2
votes
2answers
74 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 ...
6
votes
3answers
909 views

Can an antenna be too powerful for certain receivers?

I'm brand new to shortwave radio and have been researching what kind of a receiver to get. I'll use it on the antenna I'll build (longwire, 50-100 feet) for shortwave listening; no transmitting. Right ...
-1
votes
4answers
127 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 ...
1
vote
3answers
162 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 ...
5
votes
5answers
296 views

(When) does a transceiver re-reflect 100% of reflected power?

There has been a long discussion of one question here. Phil, W8II and I agreed that it's better to post a separate question. There are several sources (some editions of "The ARRL Handbook", &...
8
votes
3answers
1k views

Estimating the efficiency of a shortened (loaded) antenna

Recently I've build a trap dipole for 20/40/80m bands. I followed an article by John DeGood, NU3E and got following measurements: From balun to 20m trap: 485 cm From 20m trap to 40m trap: 362 cm From ...
2
votes
0answers
35 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 ...
3
votes
1answer
52 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 ...
4
votes
1answer
213 views

Dipole loading coil winding directions?

A single inductive loading coil in a vertical or a pair of loading coils in a dipole are commonly used to match a given total antenna length parameter to a given frequency wavelength (where the ratio ...
3
votes
4answers
202 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, ...
1
vote
3answers
111 views

Why do we need special geometry for telecommunication antennas?

In many youtube videos about building low power radio transmeters , I have seen a piece of regular wire or extension cord used as a antenna. But , it seems like telecommunication antennas have ...
4
votes
0answers
43 views

S Parameters in HFSS

I'm new to HFSS Software and I'm trying to plot Scattering parameters for a dielectric resonator excited by a probe (shown in image). I know that the top cylinder has a higher dielectric than the ...
0
votes
3answers
82 views

Is there an instance where you can directly feed a half wave dipole with coaxial cable without having to worry about balanced to unbalance?

Like the question says, can you feed a dipole with coax with no ill effects? Nothing else in the system, just the antenna and the cable.
0
votes
3answers
100 views

What happens to the signal level if the antenna has high SWR?

I'm currently reading "Reflections: Transmission Lines and Antennas" by M. Walter Maxwell, W2DU. This book explains well why the energy is not lost because of high SWR during transmitting, ...
4
votes
2answers
102 views

Stacking Two UHF Yagi Antennas

Aloha! I have two HYS TC-YG05 Yagi antennas that were gifted to me and I would like to stack them side by side ( Collinear), in the vertical orientation for some local weather balloon telemetry data ...
5
votes
2answers
87 views

what is main reason for formation of side lobes in directional antennas?

I would like to know why are side lobes formed along with main beam in an antenna. I asked one of my colleague and he explained me that its due to radiation of frequencies near to the required center ...
1
vote
0answers
59 views

Avoiding radio damage with closely spaced VHF/UHF antennas

I've mostly been using a discone in the attic so far, but now I want to get proper antennas up for 2m/70cm and gmrs. I'll probably get common commercial vertical antennas. I'm not sure how much I ...
5
votes
5answers
9k views

Does a 1/2 wavelength end-fed antenna need a good RF ground?

I was searching for DIY end-fed antenna. Some of the articles I found say that for a 1/2 wavelength end-fed I need a "small to no counterpoise" (with a lambda*0.05 m counterpoise), but some other ...
5
votes
1answer
123 views

How to compute the required length and turns for an air-cored antenna

I'm experimenting with RF reception in the 433MHz band and have made the most simple "whip" monopole antenna with 17.6 centimeters of wire. Out of curiosity, I tried various designs for the ...
5
votes
1answer
227 views

Failing to detect Hydrogen line with 105cm dish

I've seen many examples of roughly 1 metre sized dishes being used w H+ sawbird and an SDR to detect and analyze Hydrogen line signal, and have been trying myself but can't seem to get anything beyond ...
1
vote
2answers
158 views

Using a parabolic dish for working the 70cm band - Am I missing something?

I have read a lot of times in this forum that C-Band TV dishes are not suitable for operating 70cm. However: Suppose that we have a 2,4m dish. By assuming a global efficiency of a 60%, our total gain ...
9
votes
6answers
12k 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 ...
0
votes
2answers
123 views

1/8 wave 3-element 2m beam antenna

Here's what I am working on, and someone please tell me if I'm doing this right or wrong, but be kind and gentle. Center frequency 146.520MHz Driven element is 1/8 wave 10.25" long set at 6.125&...
10
votes
7answers
10k 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. ...
4
votes
1answer
101 views

Frequency selective surfaces working principle

I've seen that sometimes frequency selective surfaces are used to load a certain impedance to a certain antenna (for instance for input matching purposes). These surfaces act like a filter on the ...
4
votes
2answers
241 views

What do you call antenna that combines multiple Hustler resonators (using a VP-1) above a shared mast?

I know that a Hustler MO-3 54" mast with something like a RM-20S resonator on top is officially an example of a center-loaded quarter-wave vertical... ... but Hustler also allows you to mount ...
3
votes
2answers
180 views

Dual Polarization Yagi Antenna for 10 m

Imagine that someone has built a 4 element horizontal yagi antenna for 28 MHz with elements insulated from the boom, and with the driven element not split in the middle and using a gamma match to set ...
1
vote
2answers
209 views

Trying to identify and understand this antenna design - ground independent dual band vertical

This is the insides of a common dual band antenna 2m/70cm, made by diamond or nagoya. its generally labelled as: 1/2 wave radialless (144MHz), 2 x 5/8 wave radialless (430MHz) Its meant to be ground ...
0
votes
1answer
68 views

I have a 433MHz LoRa Dipole antenna mounted on a rocket. I am looking for a suitable Antenna to receive data from this. Any Suggestions?

The idea was to send GPS data from the rocket to the ground station at 433 MHz using a Lo Ra transmitter - mainly to help locate it once it lands and also to provide in-flight telemetry. I have a ...
1
vote
1answer
46 views

Excitation coefficient of a linear phased array

it's well known that in a linear and equispaced antenna array, the array factor is equal to: The array is then called uniform if $|I_n| = I$ is the same for all elements. The phase terms $\angle I_n$ ...
4
votes
3answers
238 views

Is an antenna always matched to free space impedance?

In this thesis the following model for an antenna is proposed: It is seen as a 2 port network, in which only port 1 is accessible (port 2 is an imaginary connection between the antenna and the free ...
0
votes
1answer
78 views

Troubleshooting the MFJ 1982 EFHW

I am a beginner with not much experience in HF. My shack consists of a Xiegu G90 connected with 20ft of RG-8x to an MFJ 1982 end fed half wave antenna. There is a small coil of coax next to the ...
2
votes
1answer
664 views

CB Radio Ground Plane (or lack thereof)

Notice the vertical antenna on the truck. I believe this first antenna is referred to as a "dipole", mounted vertically. CB to coax, coax to antenna. The shell of the truck is fiberglass. Even the ...
-1
votes
1answer
63 views

Using inverted Yagi antennas to gather and cohere RF from the sky

Imagine a group of eight or more vertical masts. On each mast is a Yagi antenna pointed upward toward the sky. The elements are inverted with the idea being that the incoherent RF coming down is given ...
2
votes
1answer
61 views

Total radiation pattern in antenna arrays

let's consider a simple linear uniform spaced array: We know that, from elementary array theory, the total pattern (for instance in terms of E-field) may be evaluated, in case no phase shift is ...

1
2 3 4 5
8