Questions tagged [antenna]
Questions about the design, selection, building, testing, mounting, or properties of antennas. See also specific tags: [antenna-theory], [antenna-construction], [dipole], etc.
929
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Using a balun with a resonant dipole
I am preparing to construct a resonant, center-fed, horizontal dipole. I have seen people use baluns at the feedpoint of the antenna, and some people swear by them, but I have never gotten a ...
- 1,891
35
votes
4
answers
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Effect of different metals for antenna elements
Other than rust, corrosion, and other reactions with air that would make the use of a metal unfavorable, how do different metals affect the performance?
Let's give Yagi an example:
Let's say I use 4 ...
- 7,530
31
votes
6
answers
38k
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Can I reduce RFI/noise at the antenna?
Recently, the power was out in my neighborhood for an extended period of time. I fired up my HF rig using battery power and was amazed at the lack of noise across the HF bands.
When the power grid ...
- 413
28
votes
11
answers
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What's a cost-effective way to boost the range of my cheap 2m/70cm handheld?
I'm a very casual/beginner level ham and as such have mostly avoided committing too much in the way of financial resources - I have a UV-5R for a personal radio, anything else I do I've used others' ...
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25
votes
4
answers
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What is the relationship between SWR and receive performance?
If an antenna analyzer shows 1:1, does that mean it's an ideal receiver as well? And what about the converse, will a well performing receive antenna show a 1:1 SWR?
I've wondered this for a while, ...
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25
votes
2
answers
5k
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How do Handheld antennas work without ground?
Dipoles have the 2 wires going to each leg of the antenna completing the circuit.
Big AM towers use the second wire as a ground plane
But how do handheld rigs transmit and receive with just one wire ...
- 7,530
23
votes
2
answers
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What makes a 5/8 wavelength vertical desirable?
An ordinary 1/4 wavelength vertical is smaller and resonant without any loading coil or matching network. What's the advantage to a 5/8 wavelength vertical? Why 5/8 in particular, and not something ...
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22
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3
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3k
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Can I build a radio telescope out of a parabolic TV satellite dish?
I have the possibility to buy a very inexpensive 2.4m parabolic satellite dish and I would like to build a radio telescope from it. Originally this dish was designed to be a satellite TV antenna.
...
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22
votes
3
answers
9k
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Why do I need to tune an antenna?
I've heard that when an antenna is set up, it needs to be tuned to reduce reflective power back into the radio. Is this always necessary, and if so how would I go about tuning it?
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21
votes
4
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How does the signal know where the cable ends and the antenna starts?
I know very little about antennas. I know, that for a certain frequency the antenna needs a certain lengths for good sending/receiving conditions.
Often the antenna is at the end of a cable. Why doesn'...
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10
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What antenna on a BaoFeng UV-5R Pro will give me better reception? [closed]
I am happy with my BaoFeng UV-5R Pro but the local UHV VHF repeater and simplex reception is terrible, even for contacts less than 50 kilometers. I assume that it's because the rubber-ducky antenna on ...
- 895
20
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5
answers
70k
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Good wire for wire antenna?
What properties should I look for in a good wire for building a wire antenna? Could anyone recommend something specific for me?
- 2,306
19
votes
5
answers
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Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?
This is something I've read in passing, but never encountered an explanation of why. For example, Wikipedia says:
Another common place one can see dipoles is as antennas for the FM band; these are ...
- 51.1k
19
votes
3
answers
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How does a mag mount antenna achieve a ground plane?
I've been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane. Consider that many mag mount antennas have some kind of protective coating on ...
- 852
19
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1
answer
4k
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How does moving a feedpoint off-center in a dipole affect the resonant frequency and resistive load?
Specifically, I understand that OCF dipoles change the SWR, but does it do this via reactance or resistance, or both?
- 1,194
18
votes
3
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What is the peak voltage at the tips of a dipole antenna?
What is the peak voltage present at the very end tips of half-wave dipole antenna in free space, and how might this peak voltage relate to transmitter type, transmitter power, RF frequency vs. antenna ...
- 13.1k
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3
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3k
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What is a "random wire antenna"?
Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system?
From everything I have heard, the resonance of the antenna (...
- 1,280
17
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8
answers
36k
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Should I chose a vertical or a horizontal HF antenna?
If I only have the budget for one HF antenna, should I chose a vertical or a horizontal antenna?
- 2,306
16
votes
13
answers
18k
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How can I safely transmit without an antenna tuner or SWR meter?
Just what the title says.
An Antenna Tuner, henceforth AT, is almost a de facto piece of equipment in a shack; working the bands without one is tantamount to leaping off the diving board into a ...
- 2,814
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8
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Are there any real advantages to an aftermarket NA-701 over the Baofeng stock antenna? [closed]
I have a Baofeng UV-5R HT radio that I have been using for about a month now and I really like it because it was very inexpensive and portable. It currently has the stock antenna on it and I have ...
- 161
15
votes
4
answers
4k
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Are there federal laws (US) protecting antenna installation?
Are there any federal laws or FCC guidelines that allow ham radio operators to install antennas?
I live in an apartment building in a large city that bans outdoor antennas. I recall reading that the ...
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15
votes
2
answers
3k
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If I install a G5RV in my attic how could I be certain there are not harmful levels of RF in the shack, or my kids bedroom?
I assume that anyone who has a G5RV or G5RV junior in their attic has done so with ceramic spacers, and has zigzag or dog-leg installations, or otherwise has contorted the antenna to fit up there.
My ...
- 895
14
votes
5
answers
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How does a folded dipole work?
A folded dipole is like an ordinary dipole, but with the ends extended and folded back, until they meet. Although it looks like a loop, I'm told it behaves similarly to a dipole.
How does this thing ...
- 51.1k
14
votes
4
answers
8k
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What does the addition of a shield to a small loop accomplish?
A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
- 51.1k
13
votes
6
answers
32k
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Calculating Antenna Length on the FCC Exam vs. in Reality
I have seen the following formulas for calculating half and quarter wavelength antennas:
Formula for $\frac{1}{2}$-wavelength antenna (in free space):
\begin{equation}
\mathrm{Length~(feet)} = \frac{...
- 1,734
13
votes
3
answers
11k
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What is the effect of using different number of radials with ground plane antenna
I'm new to electronics and telecommunication at all, I having trouble with understanding the difference between 2, 3 and 4 radials, as I've searched online I've learned that I can use only 1 radial(...
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votes
1
answer
1k
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Hanging a dipole from a tree not code compliant?
I just got off the phone with my town's electrical inspector (in Massachusetts), and he informed me that you are not allowed to hang anything electrical from "vegetation". He said if I did ...
- 367
13
votes
3
answers
8k
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Conductive boom vs non conductive boom: what's the difference on a Yagi?
I designed a Yagi antenna using 4nec2, assuming that I would use a non conductive boom.
If I use an aluminum boom but I insulate the elements from the boom, can I keep the same design? How does it ...
- 233
13
votes
4
answers
3k
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Handheld Dipoles
A problem with handheld devices is poor grounding. I read from someone else's question that dipoles don't need a ground. Why don't they make little handhelds with two antennas instead of one, or a ...
- 7,530
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3
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Is a vertical noisier than a dipole, and if so, why?
I've had people tell me, anecdotally, that a vertical is noisier than a dipole. Is this true, and if so, why?
If it is true:
Is this additional noise, such that SNR is degraded, or is the vertical ...
- 51.1k
13
votes
4
answers
4k
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Why does ice on a wire dipole affect the SWR?
We just had snow and ice overnight and my wire dipole was coated in ice. Why does the ice covering negatively affect the SWR of the antenna?
- 1,280
12
votes
4
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Are antennas circuits?
For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit?
If they are not circuits, then how ...
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12
votes
2
answers
421
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What kind of antenna is that one?
Yesterday I saw the following antenna:
I am very puzzled, at first glance it seems a simple dish but:
The mesh is really wide (low frequency?).
It is pointing to Zenith. I think that most dish ...
- 223
12
votes
2
answers
8k
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How much RF energy do trees and branches absorb?
For the 20m - 10m and 6m bands, will having my dipoles below the tops of trees (I live in redwood forests) drastically affect the RF power out or radiation patterns of my dipoles if I can still get ...
- 298
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votes
3
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Share antenna between receiver and transceiver?
I recently put up a fan dipole for 80/40/20/10. I'm looking for a way to share this antenna with a receive-only SDR and my shack transceiver. Obviously I can just switch this antenna between the two ...
- 817
12
votes
5
answers
1k
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How does an antenna transform impedances along its length?
If I insert some impedance (like a loading coil, or a trap) at the base of a monopole antenna, the effect on the feedpoint impedance is easy to predict: the impedance is in series with the antenna, so ...
- 51.1k
11
votes
6
answers
45k
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What is a Gamma match in the context of the driven element of a Yagi antenna?
How (and why) does a Gamma match work, when used on the driven element of a Yagi antenna? As shown here:
(source: http://www.iw5edi.com/ham-radio/?2-element-yagi-for-10-meters-band,49)
The article ...
- 1,280
11
votes
2
answers
709
views
How to determine if my antenna is an effective radiator?
So I build an antenna, tune it with the SWR and make it look great for a 50 ohm load.
That does not determine if it is good at getting a signal out or not, it could just be a 50 ohm dummy load.
...
- 7,530
11
votes
6
answers
3k
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While backpacking, is it worth mounting the antenna to the backpack frame (above my head)?
I am planning a trip with a large group in 6 weeks. We will be spread out in small groups on a trail in a mostly desert plateau landscape perhaps 5 miles apart, but mostly in a straight line.
I'm new ...
11
votes
1
answer
2k
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How does a "chip antenna" work?
How does a tiny surface-mount "chip antenna" for the 2.x thru 5.x GHz frequency bands work? What allows such a tiny item to radiate or receive RF with some amount of efficiency? What allows a chip ...
- 13.1k
11
votes
1
answer
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What is body blocking, and does it work with a stock HT on a foxhunt?
I've heard that you might not need a special directional antenna to participate in a foxhunt, that some people are able to use their body to help determine the direction of a signal.
How does this ...
- 12.1k
10
votes
6
answers
13k
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Can you use a satellite dish for a ham radio antenna?
Can I use a satellite dish as a ham radio antenna? I was thinking that because there are two unused, working satellite dishes that have all appropriate wires attached conveniently to the roof of my ...
10
votes
2
answers
822
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If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient?
If there are two antennas of 50 Ω and 377 Ω (same as the intrinsic impedance of air) impedance with 0 $\Omega$ ohmic resistance, and they are exactly matched with their transmission line, then which ...
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10
votes
2
answers
4k
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Can every antenna be used both for transmit and receive?
Assuming I have an antenna for receiving GPS signals, can I use it also for transmit — to create a repeater in a tunnel (or some place with no reception)?
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votes
2
answers
2k
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What is the appropriate length of an antenna for a handheld on 2 meters?
I want to upgrade the stock antenna on my Baofeng uv-5r for which I mostly use the 2 meter band. The quarter wavelength for this band is about 19.2 inches, but when I look for antennas, they are ...
- 103
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votes
3
answers
2k
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What kind of antenna has a spiral connected to a reflector like this picture?
The description on the antenna says it is used for satellite communication, but it was taken in 1984. Is this an antenna style that is still in use? What is it called? What kind of gain should be ...
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10
votes
4
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5k
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Real world performance of magnetic loop antennas?
I was investigating about magnetic loop antennas. In a paper about them I found some bold claims:
and
This almost sounds too good to be true, considering a lot of us hams are surronded by city noise ...
- 1,189
10
votes
2
answers
4k
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What determines power handling capacity of an antenna?
I just bought a cheap 1/4-wavelength, 2m. mag-mount antenna. The package says it can handle 50 watts. I can think of three things that could limit the capacity:
$I^2R$ losses in the connection to the ...
- 940
10
votes
2
answers
2k
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Buddipole model comparison
Can anyone give me some insight into the different Buddipole models available? They look pretty similar to me except for the sizes. What would make you choose one over the other?
- 817
10
votes
3
answers
593
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Using MIMO in Amateur Radio?
MIMO, Multiple Input, Multiple Output, is used widely in commercial data transmission. 802.11n and LTE devices use it to increase throughput, link reliability, and channel usage without increasing ...
- 12.1k