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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Is this amount of loss normal with LMR400?

I have a run of about 150 feet of LMR400 (specifically, it's this DX Engineering "400MAX" product). It connects to an Ed Fong antenna (2m, 1.25m, 70cm tri-band J-Pole) about 75 feet up a ...
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How can i make an ULF spiral antenna for agriculture [closed]

I have a 15 yrs persistent dreams to accomplish and i don’t know how. The frequency is between 7hz to 250hz TX in the physical appearance of spiral electric stove burner and a RX Whip rubber antenna ...
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1 vote
2 answers
173 views

Why do ham radio operators refer to current flow on the outside of coax as common mode current?

My understanding is that the desired mode of operation for a two wire transmission line is differential, where at any point along the line the addition of the voltage or current is zero, such that the ...
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3 answers
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ELF antenna receiver build instructions?

I built a vlf receiver in the nineties but good grief, that's a long time ago and have looked very little at receivers since. I'm interested in frequencies from 12 - 18 Hz. Looking at the following ...
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2 answers
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How do I rewire a simple a.m. loop antenna that became unwound?

This antenna has been around for decades and the design is as basic as can be. Somehow the antenna I'd been using, became unwound. The total length of the wire is 4.9ft. I need to know the proper ...
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1 answer
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YouLoop antenna for amateur satellite reception

I recently learned about the commercial YouLoop antenna and it seems to be quite simple to set up. They said it was possible to receive satellite signals on amateur VHF (e.g. NOAA and other CubeSats ...
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-2 votes
3 answers
82 views

Radio without antenna?

Is it possible that there will ever be a radio system that does not require antennas? (Not small embedded antennas for microwave radios, but radios that actually do not have antennas)
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-1 votes
1 answer
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Transmission power of Apple Wi-Fi antennas (EMF and health)

(I hope this is the right place for this kind of question) Background I was looking a little bit into how Wi-Fi affects our health topic. While many people seem to be concerned about their Wi-Fi ...
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9 votes
2 answers
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Why are longer antennas not suitable to pick higher frequencies?

I know that the length of an antenna depends on the wavelength of the frequency it's trying to receive. A higher frequency needs a shorter antenna and vice versa. I can see that with a high frequency ...
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4 votes
2 answers
298 views

VNA basics, antenna coax cable

Recently purchased my first VNA (Nano VNA) and I'm trying to learn the basics. I have a 150MHz 1/4 wave whip antenna that I need to install on a large metal object so I was hoping to use a VNA to help ...
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Small shortwave (20MHz) directional antenna design

I'm trying to do some basic radio astronomy experiments, and I'm currently working on picking up radio bursts from Jupiter. These are emitted at around 20MHz; for all intents and purposes, Jupiter is ...
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2 votes
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Phase-tuning Yagi-Uda antennas

Related to my earlier question around the TET-Emtron HB35C antenna. It is advertised as a: The HB35C is a full size tri-bander, efficiently utilising the DUAL DRIVE HB9CV system with the ...
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2 votes
1 answer
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Cleaning an oxidized NMO Mount

Before going through a car wash, I took my mobile antenna off its NMO mount and it looks like water seeped in through the threads. It's not corroded (i.e., there's no metal flaking off) but it's not ...
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1 answer
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AX.25 protocol packet size

I am new to the world of amateur radio and I am carrying out a university project concerning the communication between satellites and ground stations. My question is: What is the packet size of the AX....
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1 vote
2 answers
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How should coax be physically wired to a "stud" mag mount?

I picked up a variety of antennas at a swap meet a while back, and am having trouble characterizing an unlabelled HF (or low VHF?) vertical element that screws into a stud in a magmount I also brought ...
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5 votes
1 answer
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What's the effect of directly connecting ladder line to coax?

I was watching a video where ladder line (450-ohm) was directly connected to coax (50-ohm) without a matching transformer. Mating your Coax to Ladder Line Wouldn't this mismatch make it impossible to ...
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7 votes
2 answers
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Are "end-fed" antennas really more multi-band than dipoles?

Several "end fed" antenna kits (including the ARRL's for example) include wording suggesting that they are useful as multi-band antennas. But does feeding a wire antenna highly off-center ...
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Calculate antenna the length of an antenna for 477Mhz uhf radio [duplicate]

I'm very new to Ham radio and would like to know in simple terms how to calculate antenna the length of an antenna required for a 477 MHz uhf radio and or half wave or 1/4 wave whatever is better. I ...
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3 votes
4 answers
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Issues with high SWR on HF Kits EFHW 49:1 UnUn kit

I recently tried assembling a EFHW kit, and some problems came up in testing. I believe this is the kit; I bought it through ARRL: HF Kits website. This is my first time making an UnUn and EFHW kit. ...
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0 votes
1 answer
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G5RV ZS6BKW SWR problem

I bought this dipole wire antenna brand new. It came with the 1-1 Balum and 41’ of ladder line. I can only hang the wire 30’ off the ground. 11 feet of the ladder line hangs close to the ground with ...
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3 votes
1 answer
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What is this BNC-type radio connector about 13mm diameter?

What is this radio connector? LIKE BNC, but it is about 13mm in diameter, odd. Follow up: It turns out putting a sma BNC adapter in the center of it does work. In place of a "C" or "N&...
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How would I calculate the diameter of an dish from antenna gain, or effective aperture?

So far I've calculated the effective aperture using an equation. However I was wondering how to calculate dish diameter using the gain calculated earlier and if there's an equation for this?
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1 answer
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What is the best way to allow for SWR adjustment for a cubical quad?

The driven element of a multi-element cubical quad is usually made of wire, and there is no adjust for SWR. How can adjustable SWR be provided for such an antenna ? Can a gamma match be used ?
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1 vote
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How to Construct a Dual Polarization Cubical Quad Antenna for 10 m?

I want to make a four element diamond quad for 28 MHz which can be switched between horizontal and vertical polarization. The spreaders would be made of fiberglass. The coax for the driven element has ...
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36ft pole from the ground then adding 7.80 meters antenna on top is this legal

If I use a 36ft pole and a 7.80 meters antenna on top of the pole, is this going to break the law in Scotland? My antenna that I'm planning to install is a siro 827.
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3 votes
0 answers
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Building Antenna Trap: Highest impedance/lowest capacitance/greatest # of turns?

I made my first multi band antenna this weekend for 20 and 15 meters for an EFHW wire with a 49:1 unun, to be used with 5 W rig. I used a toroid I had on hand, T80-2. I hang this antenna in my living ...
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1 vote
1 answer
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Lightning Antennas 4 Element Quad Feed System Validity

I recently purchased a 4 element quad for 10 m from Lightning Antennas in USA. The antenna is designed to be mounted so the elements are diamond shaped. Notice in the picture how nice and straight the ...
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1 vote
2 answers
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Can I connect my station ground to my house's ground rod?

I'm setting up my first HF rig and I'm reading a lot of conflicting information regarding station grounding. Can I connect my HF rig/station's ground to my house's ground rod or do I need a stand-...
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2 votes
1 answer
151 views

How do phased array antennas work when they produce spot beams?

Background In a lot of literature regarding satellite communications with phased arrays, you'd see this kind of image: Conceptually, I get the basic concept of how this works - a bunch of small ...
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1 vote
2 answers
102 views

Where can I find information regarding RESONANT long wire antennas?

So multiples (by 3x-5x) of full wave lengths long? It's my understanding that you can build an antenna that is 802.28 feet long and it's naturally resonant WITH GAIN on all the usual Field Day ...
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2 votes
1 answer
156 views

The Terrestar Genus was able to talk to a GEO satellite in a smartphone-sized package, where's the antenna on this thing?

Background I'm doing some research on a company called ASTS who claims to be able to connect to regular smartphones from a satellite. Initially I wrote off their claims, but after looking into it a ...
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2 votes
4 answers
110 views

What's the methodology of MDF magnetic field antenna?

I get a MDF 9400 magnetic field antenna from school. I am not able to disassemble this flat antenna to take a picture. I am not sure if this antenna detect only magnetic field. I am not sure if ...
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2 votes
4 answers
105 views

UHF/VHF Satellite ground station with a discone antenna

I'm in the process of building an SDR-based satellite ground station using a discone. The discone is chosen due to its wider frequency range. Additionally, a dual-band LNA with around 20 dBi in both ...
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2 votes
1 answer
205 views

Resonant RF transformer using a piece of wire (no capacitors)

I previously posted this in electronics StackExchange here, but I believe Ham is more proper place for it as it closely relates to antennas. I'm curious if it is possible to build a spark-gap Tesla ...
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1 vote
2 answers
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Why do mag mounts not achieve proper grounding seeing as the coax outer connects to ground?

Diamond instructions for my CR8900 antenna state that proper grounding is required for the antenna to work. The battery negative is already grounded and has continuity to the coax outer so isn't the ...
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0 votes
1 answer
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Chaining multiple coaxial adapters

I want to connect an RTL-SDR dongle that has an MCX Female antenna port to an N-Type Male antenna feedline. I know there are thousands of pigtails and adapters for every possible need, seemingly ...
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0 votes
3 answers
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Follow Up on a previous question- Transmit antenna on HF band

I had asked a question in a previous segment and the link is provided below Antenna Size limits at 2-30 MHz (10 m to 150 m wavelength) I think i have some more clarity on the question I wanted to ask. ...
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5 votes
5 answers
292 views

Does an antenna pick up signals of all frequencies or only its resonant frequency?

I heard that an antenna picks up signals of all frequencies, and then these signals are filtered by a circuit using an inductor and capacitor, and that this is how a radio is tuned. However, I also ...
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0 votes
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What is the differece of a large loop antenna and a small loop antenna in terms of their response to an electromagnetic wave?

there is something that I dont get. I read that a small loop Antenna (also called magnetic loop) responses more to the magnetic field than the large loops does. I was wondering why this is the case ...
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6 votes
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How does Large Loop Antenna work physically?

I am learning about loop antennas at the moment. I read that the respone of a small loop Antenna is propotional to the rate of change of magnetic flux through the loop which causes a uniform current ...
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1 vote
2 answers
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Can an 80 meter band dipole work in a basement?

I don't have an HOA, but I don't: a. have the space outside for an 80 meter dipole, nor: b. does my wife want visible antennas on the outside of the house. So I've been in the mode of finding an ...
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0 votes
4 answers
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Does an RF amplifier allow us to receive a signal from further away?

From my understanding a RF amplifier boosts the transmission power of your antenna, this will in turn give you a higher gain. However I've read that this only will give you a further "...
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6 votes
2 answers
106 views

Power rating of a selfmade air coil

A colleague was winding an air coil himself. It's a 110µH coil with 200 windings for an 80m antenna, intended to be used on a 600 W transceiver. He used a copper lacquer wire with 0.6mm diameter. ...
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3 votes
2 answers
81 views

VHF Balancing, necessary? Methods?

This is a question about power dissipated due to radiation and ohmic heating caused by common mode current in the coaxial shielding, specifically at VHF frequencies. When a balanced antenna (such as a ...
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0 votes
2 answers
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SMA 3.5mm to Baofeng or similar radio

My friend just got a 2006 Chevy Calorado and it came installed with an 3.5mm SMA cable running from the roof to under the dash. It was a park ranger vehicle so it would make sense that they needed a ...
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2 votes
1 answer
91 views

Can you think of any reason my NanoVNA says my antenna has 1.2 SWR while my radio says it has off the scale SWR?

My radio is an mcHF kit that I just finished soldering up. It receives fine, but when I went to transmit it's giving off the scale SWR. I rechecked my antenna with my NanoVNA, and it shows 1.2 SWR at ...
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13 votes
1 answer
1k views

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 ...
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0 votes
3 answers
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How to transmit computer audio to a wireless microphone receiver? [closed]

I'm currently trying to broadcast my computer's audio output to a wireless microphone system receiver so that I can accompany my school's coming presentation with music. The frequency range is 480-598 ...
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2 votes
1 answer
33 views

Whip/stub antenna sorting with SA using VSWR

I have an assortment of whip antennas for various RX & HT devices such as a 2M/70cm FT740, a Uniden race scanner 29-54Mhz/108-174Mhz/406-470Mhz/806-956Mhz, a similar Realistic Pro-32 scanner and ...
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4 votes
2 answers
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Can I use my CB mobile antenna with a 10 meter radio also?

I have a mobile mounted CB antenna that has an SWR of 1.5 on channel 20. Is it possible to use it with a 10 meter radio? I do not have enough room on my car for an additional antenna, so if it is ...
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