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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2answers
43 views

Antenna phase explanation

Trying to grasp antenna phase, reading through ham.se and youtube but haven't come across a clear (enough) explanation. I understand the basics of antenna phase (i think), where E leads I that's ...
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2answers
52 views

Building a low-power simple RF frequency (433MHz or 900MHz (but not both)) detector effective at 5m with a 10mW signal

I am looking for a simple schematic for building an effective RF detector which can trigger a GPIO. The goal is to (passively?) detect a 10 mW RF signal (10% duty cycle) and have that raise voltage on ...
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4answers
919 views

Are there any antenna that can create disk like lobes?

Are there any antenna that have disk like lobes : Or are there any antenna that have very thin directivity, say lobes be no more wide than few mm.
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3answers
46 views

Loop a long wire antenna or EFHW

For a typical EFHW antenna, let's say we are in a very space-restricted environment, says a hotel room. I am thinking of the idea loop around the wire around the room, maybe even many loops. This is ...
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1answer
33 views

The HPBW of a helical antenna

can someone tell me what are the formulas of HPBW for a helical antenna? I've searched a lot and I saw that there are two different formulas of HPBW for the helical antenna, this one, and this one, ...
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2answers
70 views

Multi-wire EFHW?

I have an EARCHI EFHW (40:1 unun)antenna that I used quite successfully until it fell from a tree. I wasn't able to get it back up, so ran it along my wooden fence temporarily. Unfortunately, the ...
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2answers
74 views

What does antenna frequency range mean in practice?

I'm trying to wrap my head around software defined radios and antennas and noticed that lots of antennas are described in terms of a frequency range. For example, this one is described as operating ...
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3answers
76 views

Yagi Antenna - Elements Length

I am currently modeling a yagi antenna using Matlab and after I optimized the antenna, it gave me a director length shorter than the exciter itself (even if the optimization gave me a good gain). From ...
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2answers
107 views

Sanity check: Should I be able to hear this 20m beacon?

I’m in Sacramento and have an EFHW antenna about 30’ up. I expected to be able to hear the W6WX 14.100 beacon without issue but I cannot. The distance is about 140 miles and the beacon transmits its ...
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3answers
83 views

Radio Waves propagation (Intuitive Understanding of Wave propagation)

I have few similar questions regarding Radio waves communication particularly FM and AM type of Radio wave communication. Please bear with the naivety of the questions. Questions: Radio waves in FM ...
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3answers
74 views

Receive antenna design for large wooded lot

I've begun setting up a ham station at a rural home with a 3 acre deeply wooded rectangular lot, and a width of at least 100'. Picture shows the house portion of the lot. Currently my primary send ...
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2answers
99 views

I just can't get out on my car mounted HF

Would love some advice from you seasoned vets. I have an FT857D in my car which I tend to only use (and really want to use) when I'm stopped and setup camping. I bought a portable Windom antenna which ...
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1answer
73 views

What is the best frequency to start working EME on a budget?

Well, the title says it all: I want to start making EME contacts with the lowest possible budget, and I doubt between 2m, 70cm and 23cm. Since I cannot afford those expensive power amplifiers for ...
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1answer
68 views

Will using a loaded coil antennas have detrimental effects on QRP operations?

I was looking for a 40 m antenna for QRP CW operation at 3 W. I looked at the Wolf river coil which is a nice portable antenna. From speaking with other hams they mentioned loaded coils are poor for ...
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1answer
78 views

Yagi performing far worse than a dipole

A few months ago, I built a 6 element yagi: 3 driven elements, and 3 reflectors. For 10-15-20m. I was able to tune it to SWR 1:1 for the FT8 frequencies in each band. This antenna is only 6m above ...
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2answers
188 views

What are these antennas?

On a recent trip to China I photographed a number of "antennas" that I do not recognize. Are they even antennas?
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1answer
85 views

Questions about effective isotropic sensitivity(EIS)

Recently, I read something about EIS (effective isotropic sensitivity) and TIS (total isotropic sensitivity). I'm trying to understand the concept, but I find it's quite hard for me. In the book ...
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1answer
40 views

Effective area of a phased array

For a $N$-element planar phased array, all the elements are same isotropic antennas. Then, what is the effective area of this array? Is it $$A_e=\frac{\lambda^2}{4\pi}GN$$ where $G$ is the directivity ...
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2answers
57 views

Is a 1/4 wave vertical actually better than inverted L on 160m?

Surprisingly, I am unable to find much info comparing these two antennas. Essentially, they are the same except the one is shorter and top loaded with one wire. Does anyone have any performance data ...
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2answers
79 views

How much loss is there in traps, really?

I searched and couldn't find a direct answer so thought I'd ask. We all know the mantra "traps aren't good as they have losses", but how much loss are we talking about, really? Am I correct ...
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2answers
100 views

How does this quarter-wave stub balun work?

I was searching for 1:1 balun designs that would be efficient at VHF yet could easily be made from commonly available materials when I came across these two: While the design on the right seems ...
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2answers
71 views

How to match transmitter to Beverage antenna

Beverage antenna consist of pair of transmission lines - one being the "antenna proper", the other ground. The antenna is being fed via open feed line ( approximately 450 Ohms ) - one side ...
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3answers
108 views

What is an expected SWR plot for a trap dipole?

I've build a trap dipole for 20/40m bands. Traps are made of a coil wound on an insulator of RG213 coax and 3 kV NP0 capacitors. The impedance measured with EU1KY antenna analyzer is following: This ...
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3answers
110 views

Can a receiving antenna really be “as small as you can imagine”?

I read this antenna theory statement somewhere: And, for next-step or future thoughts: a receiving antenna can be as small as you can imagine, without loss of signal to noise. Is this BS or not?
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1answer
104 views

Double Cross Dipole antenna for 437 MHz don't tune

I'm building a Double Cross Dipole antenna for 437 MHz to be used with a SDR receiver for CW cubesat. The idea is to follow this "classic" paper from Gerald Martes, KD6JDJ. I tuned every single dipole ...
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0answers
27 views

How to cut phasing/transformer coax in a right way?

I'm building RHCP crossed dipole for 137 MHz satellites reception (I'm using 137.5 as a central frequency). My calcs are: frequency is 137.5 MHz λ is 2.18 m one dipole leg length equals to the λ/4 so ...
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2answers
61 views

Hexbeam receiving in other directions

Have a K4KIO Hexbeam up at around 20-feet on the corner of a flat metal roof pointing at 290-degrees bearing (Europe, from Sydney Australia). Currently the Hexbeam is fixed to that direction as i don'...
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3answers
74 views

What is minimum resolution for 2 frequencies to interfere each other

I started working with HF frequency. Right now, I am working with 7 MHz frequency. I have been provided a range of 7-7.5 MHz. I have to divide that range into 132 distinct frequencies to assign each ...
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2answers
43 views

RF PCB Design Difference Between Controlled Impedance Track and Impedance Matching Circuit

Im new on RF circuit designing. Im designing an circuit with GSM and GPS capabilities. I know when using high frequency signals the RF traces must be impedance matched. Now what I understand is, I can ...
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1answer
65 views

impedance matching with window twinlead

Question from new ham here, regarding ways of matching impedances between a feedline and an antenna. Is it possible to fashion a broadband HF impedance matcher from a length of windowed twinlead, in ...
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2answers
54 views

What is the formula for coupling between non-parallel wires?

I want to solve the equations for wire antennas where the wires are not all parallel. The classic method for parallel wires is to compute the magnetic potential at points on one wire due to current ...
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4answers
345 views

Any reason not to choose a discone antenna over a Wide/ MultiBand mobile antenna for TX/RX operations

We are setting up a all-band radio in an emergency com center that's intended most for amateur band use, but since its' for emergency use will also be used in the public safety bands; (150-170)MHz, (...
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1answer
38 views

On a horizontally setup 20m delta loop I am looking to determine the calculations for the proper length of a feed wire

Base of loop will be about 6 feet above ground. RG-8 or 213 will be used for the feed wire. Ugly balun as well.
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2answers
91 views

Antenna Basics - Open/Short Circuit & Half-Duplex/Full-Duplex

I am beginner in the Antenna theory and I have a few basic questions. Please help me to clarify my understandings related to the basics which I have read. And this question has 3 basic questions. ...
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5answers
304 views

Significance of 1/4 wavelength with respect to antennas

I am a new to the radio design field. My question is, 'What is so significant about 1/4 wavelength with respect to antennas.' From the information I have gathered from various sources, it is my ...
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1answer
176 views

Using a trap out of its resonance frequency?

I have a vertical antenna, about 7M total length, with a loading coil at 6M height. This is just because aluminium tubing is sold in 6 meter lengths. The loading coil is used to make it resonate at 7....
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4answers
145 views

Determining one exact antenna length for a whole band (e.g. FM/AM broadcast, Bluetooth and others)

How does a single FM antenna length work in the entire FM frequency band range, when there are theories which state that the antenna size should always be close to wavelength/4 for proper reception &...
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1answer
120 views

Grounding for lightning safety - upper floor (UHF/microwave antennas)

I have some UHF, microwave antennas and an antenna rotator on a roof mounted mast. The "radio room" is in the second floor just below the antennas. Also the service entrance for building electricity ...
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6answers
2k views

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 ...
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2answers
67 views

Setting up an Outdoor Antenna

If I would buy a ham radio with an outdoor antenna, what would I need to do to make it work (e.g can I just stick it outside) especially because I live in Miami and Miami doesn't exactly have the best ...
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7answers
145 views

Space Requirements

As I progress in my path to getting a ham license I notice that a lot of radio enthusiasts avidly talk about their radio shacks (or do they call it cabins?). Do I need that much space to start? Do I ...
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2answers
108 views

Why can't we use a simple wire for receiving 2.4 GHz signals?

I wanted to build a small drone of my own as a hobby project. My old drones were broken so I wanted to salvage as much as I could to build a small indoor one. I wanted to use an Arduino, however, I am ...
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2answers
211 views

Designing a helical antenna for a dish

I'm interested in a dish antenna with an axial mode helical feed for receiving video. My target frequency is about 1280 MHz or the 1.2/1.3GHz range. I've been able to figure out helical basics, like ...
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5answers
115 views

Can I use a 1/4 wave decoupling stub to enable mounting of a vertical yagi on a metal pole?

My understanding is that the ground plane radials used on, for example, a free standing 5/8 wave 10 m vertical antenna mounted on a metal pole, are actually 1/4 wave length decoupling stubs, the ...
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1answer
67 views

Why do some 1/2 wave collinear designs have a 1/4 wave element?

I think I understand the basic principles of a collinear antenna. How the Coaxial Collinear Antenna Works? seems to describe it well. However, I've just repaired a 1090MHz (ADS-B receive only) ...
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3answers
72 views

What kind of antenna for an automatic high bands monitoring station?

I would like to monitor NCDXF beacons, and WSPR. What kind of antenna would be good for reception in the bands of 6, 10, 12, 15, 17 and 20M? Some antennas I considered: A trapped dipole, with traps ...
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5answers
120 views

Is “coil loading” a type of impedance match?

If I have a too short dipole, or vertical, I can add a coil to lenghten in electrically. But it's my understanding that I could also do this with any other kind of match: given the complex impedance ...
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2answers
43 views

Connecting Directional Antenna To Two Antenna Ports on NIC

I want my n/ac Wi-Fi card to operate in a spatially directional manner. To achieve that I want to use a directional antenna(s). There is a slight complication though, because my Alfa AWUS036ACH ...
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2answers
162 views

Magnetic loop antenna : loops vs selectivity

I've built 2-turn magnetic loop RX antenna using 5 meters of 6.5mm copper tube. I was able to tune it with a variable air-spaced capacitor in the range of 1.8-10Mhz, but I noticed that as tuning ...
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1answer
65 views

I have a hf vertical antenna I'd like to put on my high-rise balcony

If I mount an HF vertical antenna at say a 45 degree angle to avoid a balcony ceiling, what do you suppose might happen?

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