Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
228
questions
3
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0answers
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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 ...
2
votes
1answer
38 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.
https://www.telcoantennas.com.au/...
3
votes
1answer
68 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 ...
5
votes
2answers
653 views
Why is my calculation for added length of coax for a double cross antenna different to everyone else's?
I'm an amateur amateur radio enthusiast finally building my own antenna, and have decided on a double cross antenna, with the goal of pulling data from NOAA satellites.
Four coax cables, two of ...
1
vote
2answers
180 views
Will transmitting on this antenna cause problems?
Inspired by this discussion, I wanted to check if this is something I can get away with.
I've got an old FM Broadcast antenna that came with a home stereo receiver -- it's 75 ohm flat cable, in a T ...
4
votes
3answers
80 views
Why does no one use a Buddipole as an Inverted V?
I have been looking at the Buddipole, and I've seen the most popular configuration is as a standard dipole with the arms parallel to the ground. I've also seen it configured as an upright V, as well ...
8
votes
5answers
1k views
Will electrically joined dipoles of different lengths, at right angles, behave as a multiband antenna?
I haven't seen this done, (which, after more than a century of amateur and professional radio development, is probably a bad sign), but I had an idea the other day for simplifying the setup and feed ...
1
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1answer
77 views
Colinear Vhf antenna
Textbook colinear vertical antenna designs show coax cable with alternating braid to centre configuration. Commercial whips seem to utilise a single wire as the radiating element with .66 velocity ...
2
votes
3answers
93 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 ...
1
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1answer
89 views
Mounting antenna on a metal structure? Tower/Antenna insulator?
If an antenna needs to be mounted on a metal structure what would be needed to avoid interference? Are there just some specific length to avoid or it is better to be separated by some insulator?
As I ...
1
vote
1answer
56 views
SWR characteristic changes when lifting coax off the ground?
I was at Anaheim HRO and few guys there were talking about an MFJ all band vertical antenna that does not need radials. I forget what model number it is but it is one of those "wife pleasing antennae" ...
7
votes
3answers
178 views
Passively reducing ground loss?
Would a disconnected wire or conductive mat below a low height antenna reduce ground losses?
A tuned length of wire under a wire antenna might be suitable for NVIS gain. But would a bunch of space ...
3
votes
2answers
248 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?
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0answers
28 views
Looking for a formula used by VE6YP trap calculator
I wonder whether the source code of VE6YP (Tony Field) coaxtrap design program (link 1, link 2) was ever published or described. As a Mac user I'm having little difficulties using this software and I ...
4
votes
3answers
217 views
What is the proper way to electrically wire in a loading coil to a vertical antenna?
I am trying to put together a vertical pole style antenna with a loading coil housed at the base using a plan very similar to the one described in this ARRL article. I am trying to understand how to ...
2
votes
1answer
52 views
Measurements in far field for radar cross section
I have to measure the S parameter for a rectangular sample with an antenna that works from 2 to 18 GHz. I need to measure a large band from 5 to 15 GHz and I have a problem with the known F.F. (Far ...
3
votes
3answers
133 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 ...
2
votes
1answer
62 views
Why SWR significantly changes with adding 10-30 meters of coax in presence of RFI choke?
I've build a verical for 40M band using a fishing rod as a mast, 6 radials and an RFI choke (FT240-31 ring, 8 turns of RG58, W1JR winding according to the article by Steve Hunt).
When I measure SWR ...
2
votes
2answers
126 views
Beamwidth of omni-directional antenna with gain
I am looking to buy a wifi antenna for a boat to connect to shore based wireless hotspots that may be "far" away. Due to the waves, I am assuming that the antenna mast sways +-15° from vertical. The ...
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vote
2answers
140 views
What are Smart Antennas?
What are smart antennas? How are they used in amateur radio, and how might they better than conventional antennas?
5
votes
2answers
83 views
Does a loop antenna have less susceptibility to atmospheric noise than an open ended antenna?
I always get the feeling that an antenna which has a loop for the driven element such as a folded dipole or quad will pick up less static or 'high impedance' noise than an antenna that has free ends ...
2
votes
3answers
102 views
Are standing waves on a transmission line RF or DC?
I am very confused about Standing Waves on transmission lines.
Wikipedia says "a standing wave, also known as a stationary wave, is a wave which oscillates in time but whose peak amplitude profile ...
3
votes
4answers
107 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 ...
5
votes
3answers
252 views
Determining Impedance With An Antenna Analyzer
I need some help interpreting some information from my antenna analyzer (RigExpert AA-35). I want to use the information to impedance match my AM receiving antenna system to AM radios. No ...
0
votes
4answers
110 views
Cell tower identifier antenna isolator cannon
There are several cell towers on the hills around me.
Usually I just walk around their base in a circle with
one of the many CellID apps
to get their ID. Then I can impress my friends, "That's tower ...
1
vote
3answers
94 views
Can I measure position with antenna/receiver?
I hope this question is not out of bounds. I'm a EE with little RF and you guys seem to know a LOT about RF...
I have a small vehicle traveling in a straight line at low speed. I need to know when it ...
2
votes
1answer
147 views
Bow Tie antennas impedance
I see on the internet that a radio amateur made bowtie antennas for transmitting and receiving on the 2 meter and 10 meter bands. They produced very good SWR bandwidth when fed with 50-$\Omega$ coax. ...
2
votes
1answer
104 views
What is the radiation pattern of an EH antenna?
I haven't been able to find NEC cards or pictures of radiations patterns.
I'm used to seeing them as polar diagrams, however, the only description I've gotten is "[t]he modification of the loop ...
0
votes
1answer
99 views
Can I make ferrite paint? Will it shield my antenna from my roof?
I have a 3 element vertical Yagi mounted on a rotator, and in one direction the roof of the house gets pretty close and messes up the SWR a bit.
If i mash up a few type 43 material ferrite cores and ...
3
votes
4answers
116 views
Ham operators often tell me that comparing gain to an isotropic radiator isn't much use because it's only a theoretical antenna, is this true?
When you look down on an isotropic radiator from above, ie : the azimuth view radiation pattern, it's a circle. The same as looking down on any omni directional antenna. So when comparing the gain of ...
1
vote
1answer
264 views
What is the equation for the arm lengths of a half wavelength dipole antenna?
I was operating under the impression that the arm length of a half dipole antenna is λ/4 while making one that operated at the 145Mhz frequency using a piece of 9.525 mm (3/8 inch) copper tubing, at a ...
6
votes
3answers
225 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 ...
0
votes
2answers
88 views
How can a vertical Yagi for 10 m be mounted on on a vertical metal mast and be made to work properly?
From a reply to a previous post I've been told that a horizontal tube half a wavelength long mounted right at the junction between the boom on a vertically mounted yagi and a vertical metal pole will ...
0
votes
2answers
76 views
What is the theoretical and actual cross polarization attenuation from horizontal to vertical polarization?
Can anyone tell me what the theoretical and actual cross polarization attenuation from horizontal to vertical polarization is ?
The reason i ask is that i have the idea that for receive a vertical ...
0
votes
1answer
135 views
What EXACTLY does front to back ratio mean?
For a yagi antenna for example, what does front to back ratio mean exactly ?
Does it mean the reverse gain at 90 deg behind the antenna compared to the forward gain at 90 deg in front of the antenna ?...
2
votes
2answers
145 views
What does dBi mean?
Can someone tell me what dB gain over an isotropic radiator means?
Let's say I have a 3 element vertically polarized 10 m Yagi (which I do) which is meant to have 7.5 dBi gain.
Which of the ...
3
votes
3answers
181 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 ...
1
vote
1answer
38 views
Would an infintely thin horitzontal yagi with zero height respond to vertical signals?
I can hear vertical local signals (not skip) on my horizontal yagi, and when i point it at them their signal goes up, so my horizontal yagi has some gain for vertical signals.
If the vertical ...
0
votes
1answer
53 views
Can radio waves be made to travel as or along a particle beam? [closed]
Can a laser be used as an antenna?
Can a beam of any type extend transmission distance of an electromagnetic field?
https://medium.com/starts-with-a-bang/this-is-why-the-2018-nobel-prize-in-...
5
votes
2answers
113 views
How can I calculate current distribution on an end-fed dipole antenna in theory?
I understand that in a half-wave center-fed antenna current distribution has a sinusoidal wave approximately, so the current in the center has max value and it has to become zero at the ends of dipole ...
4
votes
1answer
96 views
Are there reasons why a receive-only wire antenna should not be λ/2 in length?
The answers to this question explain why it's difficult to transfer power from a transmitter to an antenna that is λ/2 in length (or a multiple for long wires, or as half a dipole's length).
Are ...
4
votes
2answers
143 views
Yagi vs Parabolic Dish for 2.4GHz Campus Wifi from 1,800ft away?
My apt balcony is 1,812 feet exactly from my campus's Wifi access point behind a triple pane, brick, 4th floor building window. There is a clear line of sight. I was interested in seeing if I could ...
2
votes
3answers
183 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
1answer
76 views
What happens to the transmitted power cancelled out by a yagi antenna's reflector?
For a yagi antenna, for transmit, does the waveform traveling away from the driven element towards the reflector get cancelled out by the reflector and then simply disappear ? Or is that cancelled ...
-1
votes
1answer
43 views
Skin effect for a modified antenna with a high frequency pulsed DC
A direct current will be interrupted by a high frequency switch. It seems , that in a wire, connected to the source (the antenna rod), instead of pushed back- and forwards electrons, the electrons get ...
2
votes
1answer
78 views
If I point a yagi antenna at the sky, what will its azimuth radiation pattern look like?
I have a 4 element 10 m yagi antenna. If I point it at the sky, will its azimuth radiation pattern then become the same as its elevation radiation pattern when horizontally polarized?
1
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1answer
111 views
Which polarization for a Yagi antenna will have the best side rejection for received signals with vertical polarization?
I'm trying to null out vertical signals from a particular suburb which is about 40 kms away from my location by pointing a 4 element 10 m yagi such that the direction i want to null out is off to the ...
4
votes
1answer
65 views
How to model passive elements when simulating an antenna?
So I started writing an antenna simulator program to design antennas for my needs.
To calculate the electric field vector at every point, I split the active element of the antenna into a large number ...
1
vote
2answers
61 views
What would the power at output at a distance of 1cm when transmitted at a power of 1dBm from the transmitting antenna?
If the transmitter and receiver are placed one centimeter apart, what would be the power at the receiving end if the tranmission power is 1dBm?
Consider an omnidirectional antenna. And if it is a ...
5
votes
3answers
204 views
antenna in the rain
What kind of changes can be expected in the behavior (resonance, SWR, etc.) of a mobile vertical HF antenna between dry conditions and wet rainy weather? (assume a coax feed-line and low SWR in dry ...
