Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
274
questions
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For a resonant 1/2 wave dipole, does the reflections being in phase with the applied signal cause the zero reactance seen in the feedpoint impedance?
For a resonant 1/2 wave dipole when used for transmitting, does the fact that the reflected waves on the antenna are in phase with the applied signal result in zero reactance at the feed point, or ...
0
votes
1answer
59 views
Is shortening a half wave dipole to make it resonant by removing the inductive reactance a good idea?
A dipole which is exactly one half wave length allows reflections within the antenna to be in phase with the applied signal. To me it seems that this situation gives an antenna which will produce the ...
0
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2answers
102 views
For an antenna when used for transmittiing, what is the optimum radiation resistance?
For a 100 % efficient antenna, the real part of the impedance is equal to the radiation resistance.
If the antenna were a dead short with zero impedance then the radiation resistance would be zero.
...
5
votes
2answers
97 views
Modelling a folded dipole
I am looking at using NEC to model a $0.5\lambda$ rectangular folded dipole, for closely spaced larger sides (choosing a separation of $0.01\lambda$).
In Antenna Theory, Analysis and Design by ...
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2answers
108 views
What exactly makes an antenna resonant?
When an antenna is resonant, the impedance seen at the feed point is purely resistive and has no reactance.
What are the physical properties of an antenna that actually make it resonant and how do ...
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1answer
83 views
How can a half wave dipole which has an impedance of 73 + j43 ohms ever be resonant?
Is it true that for a half wave dipole, cancelling out reactance using for example a gamma match does not make the antenna resonant at all, but rather just cancels out the reactance of what is ...
2
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1answer
42 views
Can I use a directional coupler to block reflected AC current from a mismatched antenna?
Is there any kind of directional coupler device such as you find in a SWR meter that only allows traveling AC waves of one direction to pass which i could use to block the reflected wave from my badly ...
1
vote
1answer
25 views
Can received and transmitted signals on the same antenna combine to produce standing waves?
Standing waves are seen on a transmission line when for example there is a change in impedance and a transmitted wave is reflected back from one end and then the incident wave and reflected wave ...
0
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1answer
82 views
If i transmit on the same frequency using two separate transmitters joined together will they both add up in a reciever to produce a stronger signal? [duplicate]
If i were to use a passive transmit coupler to connect two transmitters of equal power output to the same antenna, and connect one microphone to both transmitters, and then transmit on both at the ...
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1answer
2k views
Why do amateur radio operators call an RF choke a balun?
When using a balanced antenna such as a half wave dipole, with an unbalanced feed line such as coax, an RF choke can be used to block RF current emitted by the transmitter from splitting up at the ...
1
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1answer
63 views
Does an antenna work the same for pure sine waves as compared to other waveforms?
Antenna theory it seems is always described assuming that the transmitted or received signal being talked about is a pure sine wave usually at the resonant frequency. Standing waves for example are ...
1
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1answer
69 views
Can any one explain E,H plane definitions?
I read in some text books that
E-plane is formed by taking constant azimuth angle and scanning elevation angle from -90:90.
H-plane is formed by taking a plane perpendicular to E-plane.
What is ...
2
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1answer
79 views
Is the voltage at the centre of a dipole zero only at it's resonant frequency?
For transmit, the voltage at the center of a dipole not cut in the center and fed with coax and a gamma match is zero in the center at the resonant frequency. This is why apparently a 'plumbers ...
0
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1answer
36 views
What is the effect of coil Q on a shortened dipole?
I made a small yagi, with the driven element being a coil loaded dipole. What is the effect of coil Q in this situation?
The coils I built are 18 turns of 1.2mm enameled wire wound tightly with a ...
2
votes
2answers
132 views
Is an antenna resonant at the frequency of lowest impedance?
I understand that an antenna is resonant at the frequency where the capacitive and inductive reactance cancel out to 0. Only the resistive impedance remains at resonance.
Does this mean that the ...
2
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0answers
54 views
Ferrite Rod Antenna Array?
The ferrite Rod is a reasonably effective Receiving Antenna for LW MW and Lower HF spectrum .It is well known that a ferrite rod is much more effective than an air cored coil of the same dimensions ....
3
votes
2answers
126 views
What kind of loop antenna is this, and what is the relationship between its diameter and wavelength?
At the bottom of webpages in the advertisement swamps I keep seeing this image of an antenna, accompanied by an offer that I won't be clicking on.
But the antenna itself looks quite intriguing. It's ...
4
votes
2answers
131 views
Actual Impedance of a folded dipole at resonance
I am using a Folded Dipole which I bought when I first got my General License. It was advertised as an all band antenna. My results with it were less than the claims made by the makers to say the ...
5
votes
1answer
287 views
How does a Viper Antenna work?
Are any of you guys familiar with a "Viper" antenna? It came up in a recent discussion with club members for higher frequency bands (6m, 4m, 2m). I hadn't heard of it before and internet searches ...
2
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3answers
125 views
High Altitude Balloon Antenna Design
I'm designing a weather balloon with a club at college. We want to build the antenna from scratch to learn more about antennas but are at a loss as to which antenna design would actually work for high ...
2
votes
1answer
59 views
Gain of Yagi turnstile?
I am currently working on a system to communicate with amateur CubeSats. I have decided to use the turnstile crossed-dipole style yagi because it is relatively easy to construct and uses circular ...
0
votes
1answer
49 views
Can you measure how much radials you are lacking for HF vertical?
I have tried mount ham sticks on SUV and a convertible use trunk lid mount, especially on 40m on the convertible I notice the SWR changes from opening the door and close the door.
Now I am quite ...
0
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1answer
69 views
Inverted L Feedpoint Height
I have this antenna EFHW 40-10 from Maple Leaf Studios. My current configuration: Inverted L with feed point 3m above ground, with "L" at 9m. I have 45 20-foot in-ground radials just below the feed ...
2
votes
2answers
79 views
Using two VHF antennas vs one because of a large obstruction
We have a VHF Omni directional antenna, 2.5 W and 119 MHZ (approximate) mounted on top of a commercial hanger. Access to the antenna is out of the question because of the lack of fall protection. ...
0
votes
1answer
72 views
Can i use an anaolgue IC switch to change a 10 m yagi's directivity by somehow combining received signals with different variable phase?
Can i use an analogue IC switch being triggered at the same frequency I am receiving on to change a 10 m yagi's directivity by somehow combining received signals with different variable phase either ...
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4answers
102 views
Which 10 m antenna will give the most rejection in one direction for received signals which are vertically polarized?
I want to null out a particular direction so that i can't receive some vertically polarized interference on 10 m coming from that direction.
Which 10 m antenna will give the most rejection in one ...
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1answer
75 views
How would I calculate aperture efficiency for an antenna?
How to calculate aperture efficiency for an antenna with the following parameters:
Big reflector diameter= 24 mm
Gain= 9.265 dbi
Frequency= 11.60 GHz
4
votes
3answers
1k views
Vertical Yagi spun at 1000 RPM: gain properties?
If I were to mount my 10 m vertical Yagi on a pole with a motor attached at the bottom with the appropriate fastening and coax mounted via electrical brushes, if the Yagi is spun at say 1000 RPM would ...
2
votes
3answers
98 views
Why is self-resonance important in a loop antenna?
I visited a "small loop antenna" calculator web site today and fed in my horizontal loop gepmetry, curious to see what it would say. 2" dia wire, 72' circumference, 3.935MHz. Interesting results, ...
2
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2answers
60 views
Will ferrite rings around a metal pole hide it in an RF sense from my vertical 10 m Yagi?
If i mount my vertical 10 m 4 element yagi directly on a metal pole so that the pole is between the elements and so messes up the radiation pattern and input impedance, if i put lots of type 43 ...
2
votes
1answer
200 views
When I am told that a dipole must have a determined length, does that include the space between both elements?
I am trying to build an antenna for receiving NOAA satellites and I need to build two 137,5MHz dipoles. When I enter the frequency and width of the wires in a calculator, I obtain that $λ/2=1.09\,\...
4
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2answers
79 views
Basic antenna matching theory?
I'm fairly new to antenna matching, other than having built a base loaded vertical.
I'm also new to EZNEC and I tried to simulate an horizontal loop. I arbitrarily chose a 10x10M loop, so I added 4 ...
2
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2answers
73 views
How to estimate a dipole feedpoint impedance?
An ideal dipole, at resonance, will have an impedance around 73 ohms. A folded dipole, around 280 ohms.
How can I calculate the impedances when not at resonance? Let's assume I have a span of 15M in ...
0
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4answers
97 views
Can I make signal transmitter without decoder?
I'm sorry if my title seems weird but I just started to learn about signal transmitting and I don't know where to start
I'm searching about simple ways to make diy radio but I can't really ...
5
votes
1answer
91 views
Counterpoise wire voltages?
One practice which seems common when operating temporary or portable QRP, SOTA, etc., is to throw a counterpoise wire out on the park lawn or shrubbery, mountaintop or hillside or parking lot ground, ...
4
votes
1answer
54 views
Voltages in a beam antenna's passive elements?
This question has good answers for the voltages reached in portions of a dipole antenna during transmit.
In a beam (Yagi or Yagi-Uda) antenna, do points along passive or parasitic elements (...
2
votes
1answer
67 views
What sort of antenna would use a bicone or lozenge-like arrangement of vertical wires?
In another QA here, there's a picture of an antenna I identified as a "discone": What are these antennas used for?
One commenter noticed that antenna was actually a "Discone, but no disc, just the ...
2
votes
2answers
120 views
Will using a 1:1 balun at the feedpoint of a center feed dipole result in no common mode current on the outside of the coax?
Will using a 1:1 balun at the feedpoint of a center-fed dipole when using coax result in no common mode current on the outside of the coax ?
0
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1answer
75 views
Passive antenna system as a Wi-Fi repeater [duplicate]
I want to extend WiFi signal using a passive repeater between two isolated boxes (have to make both box wireless).
Transmitter antenna from box A is placed in the gap between box A and B.
In the same ...
5
votes
3answers
188 views
ARRL handbook as a reference for all your radio learning needs?
Looking to take up learning understanding everything from basic electronics to how today's wideband radios work, so that I can build my own radio systems (not just ham radios), and talk radio concepts ...
2
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2answers
73 views
resonance vs resonator in antenna
Resonance in electronic means: reactance of zero. (maybe wrongly/correctly someone's calling the minimum VSWR, the resonance of antenna! and this cause confusion)
I've heard in Antenna Design for ...
4
votes
4answers
202 views
Why does an RF Amplifier fail when the SWR is high?
Exactly why does an RF output transistor fail if the SWR is bad ?
Is it A because the impedance mismatch between the transmission line and the antenna results in maximum power not being transferred ...
3
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0answers
42 views
How to simulate two antennas in 4nec2
I need to simulate 2 helix antennae placed side by side, and see the resultant radiation pattern. But after adding the second antenna with a separate and when I try to simulate 4nec2, only simulated ...
3
votes
4answers
160 views
How does the thickness of the radiator affect an antenna
Another question (Metal for antenna construction?) covered some aspected of this question, but the answers didn't exactly answer it, so I'll make it specific.
Given 2 dipole antennas, resonant at the ...
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vote
3answers
259 views
How to calculate impedance in antenna design's practice?
I would like to make a match half wave length (λ) dipole antenna (or probably a short dipole antenna). So I would like to make it by measure using LCR meter.
What I am still confuse is about what is ...
2
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4answers
196 views
What is the maximum and minimum of antenna gap of dipole antenna?
Consider the picture below is design of half wave length (λ) dipole antenna. I read some explanations saying that it is the best design to get the optimum transmit power. Half wave length (λ) is from ...
4
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0answers
71 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
1answer
119 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. That covers ...
3
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1answer
91 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
782 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 ...
