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.

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9
votes
2answers
1k views

Why is the risk of damage to a transmitter due to a mismatched antenna at lower frequencies greater?

A quick follow-up to this answer ... If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies ... I'm sorry to be so dense, but uh why is the risk ...
2
votes
1answer
432 views

Will these wires affect antenna performance negitavely?

We moved into a new house, and I noticed these wires sticking up for some sort of tent thing for shade. •I tested the wires to the 3rd prong in the outlet, and it showed a DC dead short to ground. •...
1
vote
1answer
333 views

What is the best resonator in Yagi antennas?

As we saw many design for this Yagi feed point. Q1 . Which one would be the best resonator / driven? Gamma match, T-match, delta match, folded dipole, quad, loop? Q2. And what is the reason if ...
6
votes
4answers
409 views

Weather-proofing antenna connections

Here's a problem: you buy a fancy new vertical for a fair bit of coin, but there's no coax connector on the thing. There are just screw terminals. You need to attach coax to it, but in such a way ...
2
votes
1answer
1k views

How does adjusting the sleeve on antenna traps tune an antenna?

Take for example, the Hustler 4BTV. It has traps formed by an inductor, covered by a sleeve that's connected at the lower end, and the upper end is covered by a non-conductive cap: The tuning ...
2
votes
1answer
300 views

What is this matching technique called?

I've had this suggested to match 50 ohm coax to a lower feedpoint impedance, like a vertical, especially mobile shortened verticals. What's it called? simulate this circuit – Schematic created ...
2
votes
1answer
627 views

Closest antenna to an isotropic? [closed]

What is the closest antenna ever made to an isotropic antenna? That is, has the same gain in every direction in free space?
6
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2answers
358 views

How to increase antenna aperture?

I know that in the short wavelength region, where parabolic antennas are used, the aperture can be increased simply by making the dish larger, as is the case with the radio telescopes. But how to do ...
9
votes
6answers
25k 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 ...
2
votes
2answers
119 views

Capacitance methods (antenna extensions, whole body as antenna) for receiving better

I have seen that there are times where reception isn't very good on a radio, but as soon as the hand is approached as much as possible to the antenna (with or without direct contact to the actual ...
3
votes
2answers
10k views

Spacing between elements on a Yagi antenna

Does anyone know what the spacing between elements on a beam antenna should be? I built a 146 MHz 3 element beam following instructions, and the spacing was 16" between the driven element and the ...
1
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2answers
2k views

How to make a loop antenna for HF?

While researching this answer, I came across information that indicates that a many good Low Frequency/ Very Low Frequency antennas are loops, with high directionality and good overall characteristics....
6
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1answer
260 views

How to stack circular polarised antennas

I'm interested in stacking a pair of circularly polarized "crosshair" antennas. Do I construct such as both antennas are in phase with one another then match the two signals in phase via the coax line,...
9
votes
3answers
1k views

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 ...
13
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4answers
2k views

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?
10
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1answer
2k views

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 ...
16
votes
8answers
14k views

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 ...
12
votes
3answers
3k views

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 ...
3
votes
1answer
1k views

Antenna Tripod for a vertical antenna

I'm considering buying a vertical HF antenna (Such as the Cushcraft R8), and a tripod antenna stand, such as the MFJ-1918, and setting it up on my back porch when I'm operating (Which won't be all of ...
1
vote
1answer
111 views

Comparing antenna effeciency

Let's say I have three dipoles, one is resonant at some frequency and is matched at the antenna, the second is shortened with loading coals and is also matched at the antenna, the third is shortened ...
1
vote
0answers
194 views

Designs for a multi band vertical/collinear antenna for the 1.9 gigahertz range [closed]

I'm starting to research building a multi-band antenna in the 1.9 gigahertz range. I see them offered on wireless routers, and they use them in cellular sites. Can anyone provide a reference or quick ...
5
votes
3answers
277 views

Why is gain used?

It always confused me why 100 watts out of your transmitter could radiate 200 watts coming from a high-gain antenna. Why is the term gain used instead of directionality?
8
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1answer
802 views

Is a VHF antenna on a vehicle's body a bad idea?

For context, I'm brand new, with nothing but an HT & 19" dual band (2m/70cm) whip on it. While I'll likely go with a magnetically mounted vertical antenna, I've been thinking of other more covert ...
8
votes
3answers
5k views

Why is the electric field orthogonal to the magnetic field from an antenna?

I've read in several places that the electric field is 90 degrees orthogonal to the magnetic field, and both are orthogonal to the direction of the wave from a transmitting antenna. What causes this? ...
9
votes
1answer
2k views

Antenna RX vs. TX

If I only want to receive radio signals and not transmit, are there any differences in the way I design the antenna I need to use, or is it the same either way? I was going to pick up a Realtek ...
5
votes
1answer
1k views

Why is optimal polarization different for fm as to SSB/CW

On the article "7db for 7 bucks", which is an article about building a simple three element 2M yagi, they stated that vertically polarizing the antenna is better for FM work, and horizontally ...
8
votes
2answers
221 views

What will I need to receive the ICE/ISEE-3 transmitter?

The ICE/ISEE-3 spacecraft, launched in 1979, is due to pass by the earth in August, 2014. It was commanded to power down completely years ago, but it appears to have failed to do so, and while it ...
9
votes
2answers
2k views

Are satellites Left or Right hand circularly polarized?

I'm thinking of building some helical antennas for satellite work. I want to know which way to wind them. If satellites are spinning randomly, how can we know if they are left hand or right hand ...
2
votes
1answer
3k views

What is the theoretical performance of a 2m 1/4 wave ground plane antenna when used at 70cm?

If I have a 2-meter 1/4 wave ground plane antenna with 1/4 wave radials bent down at approximately 45 degrees, what kind of performance in terms of SWR and gain pattern can I expect when using it on ...
6
votes
6answers
4k 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 ...
14
votes
2answers
2k views

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 ...
8
votes
3answers
579 views

How would I calculate antenna gain?

The concept of antenna gain is pretty important for calculation of link budget and is something I've had contact with. I know that it tells me how focused the waves emitted by the antenna are and I ...
4
votes
1answer
292 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?
2
votes
1answer
217 views

Maximum Input Wattage of MFJ-1717PL Antenna

I was wondering if anybody knew the maximum input wattage of the MFJ-1717PL Antenna. I was going to use this with the Yaesu FT-1900R mobile radio mounted in a Pelican case.
19
votes
10answers
82k 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 ...
3
votes
2answers
355 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 ...
3
votes
6answers
3k views

Smallest HF antenna for DX?

There seem to be reports of people trying to see how far an HF DX contact can be made using the tiniest transmit power (mW or even sub-mW QRP). But many of these contacts seem to be accomplished ...
1
vote
1answer
2k views

Patch Bowtie Antenna Design

I would appreciate it if someone could help me in designing a patch bowtie antenna. I would like to know the frequency and the bandwidth in terms of the length, angle and the length and width of the ...
12
votes
3answers
8k 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 ...
4
votes
2answers
2k views

Can an HF antenna be put inside a tree?

There are some trees around with branchy tops that seem wider than half of 10M, maybe even half of 20M, and above the nearby rooftops. Can a wire dipole or a vertical be mounted inside a tree? If so,...
32
votes
2answers
43k 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 ...
5
votes
2answers
6k views

How to construct a loop antenna for receiving HF?

I have a unused hula-hoop in my garage, and I ran some stranded speaker wire around it once, and attached one side of the wire to the coax shielding, and the other to the coax core wire. Is this the ...
1
vote
1answer
2k views

Homebrew 2 meter Yagi construction

Here is what I have • A Baofeng Uv-82 transceiver • A 1/2 inch 10 foot PVC pipe • 3 1/4 inch x 36 inch Aluminum rods • 2 1/4 inch x 48 inch Steel rods (I know they'll rust, it's just temporary to ...
4
votes
3answers
515 views

Height and feedline loss tradeoff for VHF

Currently my 2m antenna is about 3m above the ground inside, my HF antenna is connected to 30m (2db loss) coax and is about 12m up. Since the loss for 2m is a lot more when traveling down such a long ...
6
votes
1answer
671 views

What should I look for in an antenna for a DVBT Dongle used for SDR?

I use a cheap DVBT dongle that I control via RTL-SDR. Right now a very basic setup. The general consensus seems to be that a long usb cable should be used (to keep noise from the computer away from ...
5
votes
2answers
4k views

What are some good options for covert dual band vehicle antennas?

Would like to have a 50W mobile in my SUV, but I'm not allowed to have a big whip on the outside. What 2m/70cm dual band antennas are available that don't say, "Ham Radio Operator"? Are there three ...
2
votes
2answers
163 views

Measuring antenna characteristics without physical access?

There is a loop antenna that was thrown around an attic interior several decades ago, of long forgotten dimensions. I found the feed line. Is there a way to measure what (U.S. amateur) bands on ...
9
votes
2answers
716 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 ...
2
votes
2answers
1k views

Does increasing the number of turns on a loop antenna decrease frequency operation?

Lets say I want to make a VLF loop antenna for a Sub AM radio band. I don't want a full wavelength because that would be a humongous antenna. Would I wind more turns of wire to decrease the frequency ...
2
votes
0answers
529 views

The knob on rabbit ears [closed]

So I was reading some fiction about where the character bought a television and "and the fanciest pair of rabbit ears available. The rabbit ears even had a large tuner knob built in to it that I'm ...