Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
369
questions
4
votes
1answer
104 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
64 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
...
-1
votes
4answers
119 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
0answers
36 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 ...
1
vote
3answers
152 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 ...
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 ...
3
votes
4answers
189 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
107 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
5answers
283 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", &...
0
votes
3answers
93 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, ...
5
votes
2answers
83 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 ...
4
votes
2answers
88 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 ...
1
vote
0answers
57 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 ...
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 ...
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
223 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 ...
0
votes
2answers
116 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&...
1
vote
2answers
138 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 ...
4
votes
1answer
100 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
230 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
171 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
167 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
62 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
45 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
219 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
72 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
58 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
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
0answers
41 views
Printed Dipole Transmission Line Equivalent Model
let's consider a printed dipole on a substrate with a GND plane:
I've seen many times an equivalent model which uses transmission lines like this (reference):
This model is useful to understand the ...
2
votes
1answer
55 views
Phase shifts in antenna arrays
Let's consider a simple antenna array. For instance, this three-elements equispaced dipole array:
Each dipole is connected to a signal voltage source. It's well known that it's possible to choose the ...
3
votes
1answer
41 views
Fourier transform of air breakdown impulse waveform
i am a beginner on signal processing.
I learned from some papers, site online, including this forum that lightning discharge or any electrical arc emits wideband radio frequency. because the odd ...
2
votes
3answers
115 views
Receiving multiple signal
Maybe this is a really silly question even from me, a completely amateur...
But I like to know about how's the antenna output when its receive multiple signal
Is it possible different signals on ...
4
votes
3answers
227 views
Electromagnetic signal from spark gap
I am a power electrical engineer college student, and I have a project to make an antenna for magnetic direction finding.
My main topic is to detect lightning strikes, but its to hard due to ...
-5
votes
4answers
206 views
Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?
Lots of explanations i've read on the internet written by ham radio operators and in some text books state that a half wave dipole is resonant when the inductive and capacitive reactances cancel out.
...
0
votes
0answers
101 views
Long wire antenna end fed random length folded back on incline
Trying to lengthen my 10mtr. end fed to 39 metres in length. To do this I need the first leg (10mtr.) to run at a lower height approx (5mtr)turning back on a dog leg, and the final 29 meters then ...
3
votes
3answers
277 views
Use (TV?) Log-Periodic antenna for VHF
I found this old log periodic antenna that I assume was from a TV. Could I, or how would I, use this on the amateur radio bands? My main focus would be VHF, with UHF being secondary and HF would also ...
2
votes
2answers
116 views
Magnetic loop antenna: Which side of conductor is the current due to skin effect?
Contemplating a big magnetic loop antenna.
Would a wide copper strip be better than a tube with the same conducting surface?
Where will all the current be due to the skin effect?
Would a flat ring be ...
1
vote
1answer
59 views
Dual Rubber Ducky antennas
Can I use 2 identical rubber ducky antennas with a splitter on my CB HT radio to improve range?
0
votes
3answers
81 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.
2
votes
3answers
148 views
How do 'plumber's delight' type Yagi antennas have a bandwidth?
For Yagi antennas where the driven element is electrically connected to the boom like the parasitic elements, how can this function without diminished performance outside of the design frequency? In ...
1
vote
1answer
47 views
How to calculate of shielded loop antenna correction factor without extra antenna measurements
A lot of article about 60 cm shielded loop antennas and how to measure antenna factor using antennas with already known antenna factor.
But for example if I have one shielded loop antenna (...
1
vote
1answer
88 views
What length and number of radials should be used for a dual band vertical whip backpack antenna?
The Situation:
Very new Ham
I have a 2m/70cm 48" Abree whip antenna, originally designed to be connected directly to an HT
I would like to mount this antenna to the side of my hiking backpack, ...
3
votes
3answers
75 views
Recommendation for hobbyist flight computer radio antenna
I'm a CS college student working on the flight computer of my Rocketry Club's rocket. My flight computer has a 915MHz radio transceiver, and it needs to transmit data to my computer with another radio ...
2
votes
1answer
100 views
Substitute a car roof with radials?
I have a K40 Plus CB antenna, which is supposed to be attached to a car roof for the ground plane. However, I would like to set this up as a base antenna. Could I instead attach the ground to separate ...
1
vote
2answers
111 views
How many turns of wire inside 60 cm shielded loop antenna (9kHz - 30 MHz). How can I find this number without destroying the antenna?
Lots of information about shielded loop antennas is available on the internet. However, antenna manufacturers do not indicate the number of turns. How can I find the number of turns of a manufactured ...
0
votes
1answer
58 views
Stacked Yagi Gain calculation
I had a quick look at a practice exam for the license in my country and had a question on stacked Yagi antenna. I have been looking around but the only thing I can find is the mention of an additional ...
0
votes
1answer
44 views
Can I slant-polarize a bay antenna?
I am trying to work a 700mhz LTE signal with a DB2 uhf bowtie television antenna. I find the cellular signal to be horizontally polarized. Can the bowties simply be twisted 45 degrees in both ...
2
votes
2answers
203 views
How does a 40/15m dipole with capacitance hats work?
I followed an article Antenna Here is a Dipole [PDF] by James Hearly, NJ2L to build a dual band 40/15m dipole:
The antenna works more or less as expected. My 40m dipole was resonant at 7.030 MHz and ...
0
votes
1answer
75 views
60cm 9 kHz 30 MHz Shielded loop antenna behavior as a transmitting antenna
I know how shielded loop antenna work as a receiver antenna. (How behave electric and magnetic field).
But I can not understand how shielded loop antenna works as a transmitter.
Will it produce only ...
