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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4answers
174 views

Partially Collapse Telescoping Antenna to Change Effective Length

I recently purchased a cheap RTL-SDR kit to experiment with SDRs and different frequency bands. This kit came with 23cm and 100cm telescoping antennas. I now wish to use the 100cm antenna to pick up ...
4
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2answers
188 views

Antenna suggestions for 160m band in smallish yard?

I have a decent-sized but not huge yard (roughly 50x100' / 15x30m) and I'd like to get on the 160-metre band. It's hard enough to get out on this band so I'm looking to do something reasonably ...
4
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3answers
154 views

Substitute for Dacron rope in antennas

I am building an antenna that specifies the use of Dacron rope to help support the spreaders, but that is not readily available in Trinidad and Tobago. What will be a good replacement with regards to ...
4
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1answer
147 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 ...
4
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1answer
728 views

Antenna, input and ground bonding

I'm new to this and am in need of guidance. I am mounting a multi-band antenna on a 50 foot tall 1 1/4" galvanized mast. I plan to drive a ground rod at the base of the antenna and bond the mast to ...
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3answers
335 views

2m Biquad - Why not?

I'm thinking about putting together an Echolink link node on my local repeater frequency so I can participate in the weekly net when out of town. This seems straightforward as it's simply: Being in ...
4
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1answer
1k views

What frequency to set trap on?

I plan to build trapped multiband dipole so I read lots of documentation I found. There is one thing that confuses me: various authors recommend setting resonant trap frequency differently: some say ...
4
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3answers
86 views

Do resonant antennas actually resonate?

Do resonant antennas actually resonate (in the lumped circuit sense, exchanging stored energy between inductive and capacitive elements at a natural oscillation frequency)? If so, can this resonance ...
4
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2answers
399 views

How should I mount a mobile antenna on a vehicle with a non-conductive body?

I would like to mount a self tuning antenna, ATAS-120, matched with the FT-857D transceiver. I would like to make this pair function on an ARGO 8x8 amphibious vehicle with a polyethylene body. There ...
4
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2answers
3k views

Can I ignore the radial elements of a 2m/70cm antenna if it's on a metal roof?

I'm looking for a dual band base station antenna, and find that many of them have short radials around the base. Due to the specifics of my installation, I need to remove them. However, it is being ...
4
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1answer
1k views

Does a larger Biquad antenna give better results?

Consider a biquad antenna used for receiving, not for sending. They are typically built with each side having a length of $\lambda / 4$. If a biquad antenna was built with a side length of $\lambda / ...
4
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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?
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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,...
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2answers
830 views

What impedance matching do I need between my 300Ω feedline and Softrock receiver?

I will be assembling a Softrock Ensemble II HF receiver, and I know I'm going to want it on air as soon as I build it, so I'm challenging myself to build an antenna for it first. The plan is to do a ...
4
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2answers
114 views

Why a capacitor is needed in Fuchs antenna?

I tried to understand the physics of Fuchs antenna and there is one thing that I don't quite understand. This is probably a very silly question, but I spent a lot of time looking for an answer (books, ...
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2answers
137 views

100MHz to 1000MHz Antennas for Transmit and Receive

I am building a ground and wall penetrating frequency modulated continuous wave radar. The only components that I have not been able to track down are the antennas. I need two antennas (one for ...
4
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1answer
402 views

DAB antenna in roof space

We are setting out our roof-space as an attic, and after decorating, there will be a triangular void under the house ridge, which will be about 36" wide, and 18" high. I can easily fit a standard ...
4
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2answers
813 views

Cross Yagi Antenna Design

What will be the effect if I add the insulation between elements and metallic boom of the cross yagi antenna (where elements from outside of the boom, instead of through boom) and in this case boom ...
4
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1answer
2k views

How to measure gain of an antenna?

I have dual stacked crossed yagi antenna. How can I practically measure the gain of the antenna combination? I know that this can be done in an anechoic chamber. But this is not feasible for me (...
4
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2answers
201 views

Antenna Design for specific directions

I am designing an antenna for a device and was hoping to gain some insight in the correct design direction for the antenna. The Idea: A receiver & antenna that fits in a 6" diameter by 3" deep ...
4
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1answer
83 views

Dipole symmetry?

In ideal free space, both arms of a tuned wire dipole will be of identical length. However, the real world is not perfectly symmetric free space. The support heights, ground levels, ground ...
4
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1answer
697 views

What is the difference between “Cross Polarized” vs “Circularly Polarized” Antennas?

What is the difference between cross-polarized yagi antennas and circularly polarized antennas?
4
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1answer
513 views

How to bypass LNA for TX in UHF Antenna?

I want to work with amateur, low power, and/or pico satellites. I would like to use an Eggbeater or Turnstile antenna with my UHF 433 MHz radio, since those antennas are very cheap and easy to build ...
4
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1answer
210 views

How far the near-field reactive region extends from the transmitting antenna?

I am doing research on near-field harvesting. In my situation the transmitting antenna is a dipole antenna operating at 2.45 GHz and its length is 14 cm long. I am trying to find how far near-field ...
4
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1answer
601 views

Correct number of elements in 4nec2 antenna simulation

I am designing a 1.25-wavelength dipole antenna with the 4nec2 software. What I noticed is that the input impedance of antenna is changing greatly when I change the number of segments. How many ...
4
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2answers
2k views

Does antenna width/shape affect resonant frequency like length does?

I was wondering if I made an antenna from a Rohn 25G tower, would it have the same resonant frequency as a pole of the same height (assuming guys are insulated)? Also with the Rohn antenna, the waves ...
4
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0answers
57 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 ...
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4answers
782 views

Is a copper J-Pole antenna better than a Slim Jim for transmitting?

I live in a fairly sheltered valley but there are several hill-top VHF repeaters that I can receive very well. However the one repeater in particular I want to transmit to, I can't reach well. I ...
3
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3answers
412 views

The right antenna size

I'm preparing for the USA Technician exam and I was reading in the manual that the ideal size for a dipole is following this strange formula: 1/2-lambda. But based on what I read after, it seems it ...
3
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5answers
303 views

How should I select an HF antenna for portable work?

I'd like to get started doing portable HF work and I'd like some information on antenna possibilities. My broad (and somewhat flexible) criteria are: By "portable" I mean it can be carried in a ...
3
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2answers
717 views

Does a receiving antenna need radials?

I am very new to radio and am using two 433MHz 1/4 wavelength monopole antennas to send and receive data. On the transmitting antenna I'm going to add radials (as it is the standard in my application)...
3
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4answers
142 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 ...
3
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3answers
480 views

How thick should counterpoise wires be?

I would like to use a shortened whip antenna with a coil in it's base, e.g. OPEK HVT-400B. My transceiver maximum power is 100 W (and antenna's - 120 W). To make the antenna work I need counterpoise ...
3
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4answers
179 views

NMO bicycle mount antenna has unexpected SWR

I built a bicycle antenna mount featuring an NMO connector to allow quick changes. With a 2m 1/4 wave monopole it gives reasonable SWR results (1.4 or so in the band of interest), with a particular ...
3
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2answers
132 views

What are these antennas used for?

I noticed this antenna park in Heidmoosstrasse, Switzerland. What is it used for?
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2answers
804 views

Antenna polarization when dealing with satellite communications

It's easy to understand, conceptually anyway, the difference between a horizontally polarized antenna and a vertically polarized one, when referenced to ground. However, when they are pointed nearly ...
3
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2answers
2k views

How to recieve a signal from multiple sources simultaneously (helical antenna)

I'm working on a system (theoretical at the moment) whereby I wish to receive data from multiple sources all transmitting at the same time. I've read that a helical antenna is capable of this. I'm ...
3
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2answers
1k views

How do I determine which HT antenna is better based on their very similar catalogue descriptions?

I'm considering getting an after-market antenna for my new 2 m/70 cm HT and am trying to decide which of the two antennas I should get. My primary reason for considering an alternative antenna is ...
3
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2answers
1k views

Optimising a small magnetic loop with 1:1 SWR but little radiation

I'm trying to build a small magnetic loop for 5W on at least 40m - 20m following ideas of G4ILO's wonder loop. For this, I'm using coax with a ~2mm copper core and ~1mm spacing to the braid (see 1st ...
3
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3answers
560 views

Why does an “electrically small” antenna have narrow bandwidth?

Reading this interesting piece on magnetic loop antennas, the author explains that a magnetic loop has great efficiency even at small size, but the the price you pay is very narrow bandwidth. Why is ...
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3answers
153 views

How to Measure Signal Strength

I am building several types of radio antennas, and I would like to test which is the most effective. I am wondering: What is the best way to measure the strength of the received signal? It is at ~151 ...
3
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2answers
619 views

proximity of rain gutter to dipole antenna

I am a new ham and wish to mount a center-fed G5RV dipole antenna under the eaves of my house, where I have a 78' clear run available two stories above ground. The problem is a metal rain gutter which ...
3
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3answers
1k 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 ...
3
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3answers
653 views

What is the point of high gain antenna with respect to the maximum EIRP

OFCOM states that the maximum EIRP within the UK for 2.4 GHz is 100mW. Simply put, what is the point in being able to buy 2.4 GHz high gain antennas which can say do 24dBi, which already puts the ...
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3answers
237 views

How do you keep your vehicle clean with a mobile antenna?

I want to add a V/U antenna to my truck, but my wife started asking about weather proofing and car washes and I had no answer. How do you keep your vehicle clean after installing a new antenna, and ...
3
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1answer
444 views

Receiving through a linear amplifier

I want to build a simple amplifier using those Mitsubishi modules (like the RA30H1317M or other RA parts). I know this might seem like a very obvious question, but I am unable to find the answer after ...
3
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2answers
3k views

Tuning/trimming a ground plane antenna

I've built a ground plane antenna with a 19.5" vertical and 4 20" radials. Currently, at 147.135 MHz my SWR is 3:1, clearly not ideal (and even bad for the transmitter!). I'm reluctant to start ...
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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 ...
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4answers
742 views

Is string trimmer line suitable for supporting antennas?

In searching for suitable materials for a wire antenna, I found a few mentions of using string trimmer line to hold up each end of the antenna. This would be a nice option as it is readily available ...
3
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3answers
126 views

Applications for 100 GHz band?

I was reading this paper and I found it very interesting and the following question came up, What are the main applications (what is used for) 100 GHz band? I couldn't find any reference on what is ...