Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
382
questions
3
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2answers
77 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:...
0
votes
1answer
42 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 ...
0
votes
2answers
72 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 ...
3
votes
5answers
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 ...
2
votes
1answer
90 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 ?
3
votes
0answers
49 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 ...
5
votes
5answers
221 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....
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 ...
5
votes
2answers
307 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 ...
0
votes
3answers
118 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 ...
2
votes
4answers
177 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 ...
1
vote
2answers
92 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 ...
0
votes
1answer
59 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
149 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
75 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
128 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
2answers
177 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
163 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
36 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
213 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
114 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 ...
5
votes
5answers
303 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
104 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
93 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
120 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
63 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
46 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
125 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
228 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
129 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
175 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
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
247 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
188 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
249 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
70 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
47 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
249 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
83 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
63 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
64 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
44 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
57 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
43 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
120 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
240 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
262 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
125 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
303 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 ...
