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.
138
questions
41
votes
7
answers
45k
views
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
25
votes
4
answers
17k
views
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, ...
- 622
11
votes
6
answers
45k
views
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
14
votes
4
answers
8k
views
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
9
votes
1
answer
720
views
Why must twin-lead conductor spacing be small to avoid radiation?
A transmission line does not radiate when the spacing between the two wires is very small when compared to the wavelength, but the transmission line begins to radiate when the spacing between the ...
- 193
7
votes
5
answers
12k
views
Wifi passive repeater (antenna to antenna connection)
I have two buildings. Building A has wifi (2.4GHz) infrastructure, Building B doesn't. One side of building B can pick up the wifi signal from building A. I want to passively extend the signal through ...
- 171
35
votes
4
answers
55k
views
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
19
votes
1
answer
4k
views
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
6
votes
2
answers
6k
views
How does a folded balun work?
A folded balun is made from two quarter-wavelength, parallel conductors. A picture is worth a thousand words:
Here are some pictures of an actual construction from Gisela & Joe Noci on diydrones....
- 51.1k
22
votes
3
answers
9k
views
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?
- 1,734
18
votes
3
answers
14k
views
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
13
votes
4
answers
3k
views
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
17
votes
8
answers
36k
views
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
13
votes
3
answers
11k
views
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(...
- 233
5
votes
2
answers
15k
views
What is the aperture efficiency of an antenna?
For reflector antennas, I see a number called aperture efficiency. What does it mean?
3
votes
3
answers
8k
views
Calculating bandwidth of antenna?
Is there a way to calculate bandwidth of an classical dipole antenna having this information:
center frequency
wire velocity
wire diameter
I would disregard antenna height, to simplify.
I am not ...
- 872
31
votes
6
answers
38k
views
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
25
votes
2
answers
5k
views
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
14
votes
5
answers
6k
views
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
13
votes
6
answers
32k
views
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
9
votes
6
answers
39k
views
Is there a simple, DIY, antenna suitable for HF receive only?
So the antenna I'm thinking about doing might be* way too large for my property.
Is there another simple, cheap, DIY antenna I could try on my receiver? I know I'm going to want to hook it up and ...
- 12.1k
9
votes
1
answer
4k
views
How does a slot antenna work?
How does a so-called slot antenna work? How can one construct one? What might be the radiation pattern and efficiency compared to a wire antenna?
And, if a small slot antenna "works" at mobile ...
- 13.1k
9
votes
6
answers
8k
views
Why is antenna aperture a function of wavelength?
Wikipedia says:
It can be shown that the aperture of a lossless isotropic antenna, which by definition has unity gain, is:
$$ A_{\mathit{eff}} = \frac {\lambda^2}{4 \pi}$$
We also see this emerge as ...
- 51.1k
3
votes
1
answer
419
views
Is it possible to make a shield that blocks time-varying electric fields, but not time-varying magnetic fields?
Take, for example, a shielded loop antenna. It is often claimed that the antenna is inside the shield, and the shield blocks electric fields from reaching the antenna, while allowing magnetic fields ...
- 51.1k
23
votes
2
answers
18k
views
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 ...
- 51.1k
20
votes
10
answers
97k
views
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
votes
5
answers
70k
views
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
15k
views
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
16
votes
13
answers
18k
views
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
13
votes
3
answers
5k
views
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
10
votes
2
answers
822
views
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 ...
- 203
9
votes
2
answers
14k
views
Connect two receiving antennas to the same radio
I have built a 1090 MHz ADS-B antenna roughly following some video instructions. It appears to work reasonably.
However, because of how it is placed, it captures signals for more or less a half of ...
8
votes
2
answers
4k
views
How does a Dual Band Handheld Antenna work?
Looking to get a (highly recommended) NAGOYA NA-771 37cm "Dual band (2M/70cm) handheld antenna" for my Baofeng UV-5R.
If my math is correct - this is about a half-wavelength antenna for 70cm, but ...
- 213
8
votes
3
answers
865
views
What gain do I need to talk to SO-50 with my HT?
My HT has 5 W of power, a sensitivity of about 0.2 µV, and I would like to talk to the SO-50 with it. How much gain do I need in my antenna to make this work?
- 6,093
7
votes
8
answers
12k
views
How does the length of a metal sleeve around a (shieled) coax cable affect antenna performance?
A post on http://adsbexchange.com/forums/topic/beginners-2-cantenna-easy-diy-antenna-to-improve-rangeplane-count uses a $\frac{\lambda}{4}$ sleeve made of a pop can beneath a $\frac{\lambda}{4}$ wire ...
- 73
6
votes
2
answers
1k
views
Does a tube based HF transmitter need an antenna tuner?
With the adjustments on a transmitter such as a Yaesu FT-101E, is there any purpose for an antenna tuner, or can you accomplish the same thing by adjusting the loading and other controls?
- 622
5
votes
2
answers
7k
views
What is the impedance of a 1.25 λ dipole antenna?
I would like to make a dipole antenna. This particular antenna is used for reception only; no transmission is involved. I would like to receive as much power as possible by this antenna as it is used ...
- 449
5
votes
2
answers
270
views
Will a HF beam antenna on rooftop building interfere with other antennas there
I am moving into an apartment on the top floor of a building and I intend to install a HF beam antenna for 20 to 10 meters, on the rooftop of the building.
I notice that there are already some ...
- 568
5
votes
2
answers
1k
views
Can antennas have reverse harmonics
I know antennas can have 1/4 wavelength, 1/8th etc. but if you are operating from UHF bands, can the antenna be lets say twice as long?
- 7,530
4
votes
1
answer
338
views
How does a higher antenna reduce rain static on a lower antenna?
I have operated at several stations - including my own - where a 40m beam is stacked above a tribander. During a rain storm, there is so much QRN on the 40m beam that the band is unusable, but the ...
- 7,798
4
votes
1
answer
106
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 (...
- 13.1k
4
votes
1
answer
429
views
What is the average fade margin required for proper operation at 2.4 GHz?
I have two radios. Sensitivity is -84 dBm and transmitting EIRP is +30 dBm. How much distance should I expect?
I want it to be somewhere near about 2-3 km. Is it possible?
- 225
3
votes
3
answers
3k
views
Broadband antenna for SDR radio
I recently bought a very wideband SDR receiver (DX-Patrol MK4, declared covered frequencies are 100kHz-2GHz). I'm experimenting with antenna designs because unfortunately I live in an apartment ...
- 319
3
votes
1
answer
706
views
Idea for better reception in crowded city
I am living in crowed area of a city. It is impossible for me to set up an antenna outside the apartment. I receive signal inside the room.
I have a funcube dongle pro+ and some RTLSDR, the picture ...
- 353
3
votes
3
answers
4k
views
Choke at antenna and feedpoint?
I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I ...
- 817
3
votes
2
answers
469
views
How can I know over what distance or at what speed I can communicate? [closed]
Given some description of some parameters like:
transmitter power
frequency
antenna
location
time of day
how can I know over what distance communication is possible? Can I know the limits to these ...
- 51.1k
2
votes
5
answers
4k
views
Balun and tuner configuration for multiband dipole
I'm putting up a multiband dipole in some tall trees. (Perhaps it's more correct to call it a "dipole-doublet"). The situation I'm imagining looks like this:
The legs of the antenna are each 100 ...
- 255
2
votes
2
answers
2k
views
High data rate on HF & MF bands
Is it possible to transfer data at a high rate, like 1-2 Mbps, on 0.5 - 30 MHz?
From Shannon's Theorem, with a bandwidth of just 300 kHz it is possible to reach 1.5 Mbps.
I want to use these bands ...
- 213
2
votes
2
answers
691
views
Could I expect 12 mile range with the GXT1000VP4 radios?
I’m considering buying a Midland GXT1000VP4 radio set from amazon here: https://www.amazon.com/dp/B001WMFYH4/ref=cm_sw_r_cp_api_6BfmBbBQZ5VBY
In Suburban Pennsylvania how much range could I expect ...
- 156
2
votes
3
answers
817
views
Packet Radio at 100 miles [closed]
I am wanting to assemble a Packet Radio solution that will allow for packet radio transmission with a range of about 100 miles or better. I am not sure what band to use, what radio to use, what ...
- 21