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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7
votes
2answers
2k views

Practical 80m vertical wire antennas without radials?

We'd like to install an antenna for 80m at our club/contest station. Our club, OH2K, is housed at a school, and we can't fill the roof with a radial mesh. The roof is not metallic itself, either. We ...
7
votes
1answer
396 views

Is it safe to mount an active scanning antenna close to an hf antenna?

I live in the centre of a seaside town in the UK. Because of lack of space I have a random wire antenna in the loft of a small house, and pick up a lot of noise on the top band Sunday morning CW ...
7
votes
1answer
585 views

Is bending the tips of the antenna wires going to affect the effective length?

I'm looking at designs for low cost DIY yagi antennas for a fox hunt, and pondering coat hanger wire and PVC piping. I'd like them to be built by the youth who will be doing the fox hunt, but that ...
7
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5answers
219 views

Coax fed dipole: shield goes to one side, yet is grounded via chassis line to Earth

Suppose I have a coax-fed half-wave dipole antenna. The coax shield goes to one side of the antenna, the center conductor to the other side. The transceiver's chassis is connected (via the coax ...
7
votes
1answer
394 views

How to make a ferrite bar antenna for RTL-SDR?

I bought a RTL-SDR (blue one with little MCX antenna). I modified its Q branch, and can receive short wave radio with Degen 31MS antenna now. For MW, Degen 31MS antenna has a ferrite bar antenna ...
7
votes
1answer
355 views

Simple cheap foxhunting?

I'm currently looking to do a foxhunt for a youth group, and need to keep it inexpensive and easy enough that it won't be impossible for those new to foxhunting and ham radio, but difficult enough ...
7
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2answers
650 views

Simulating two antennas (transmitter and receiver) using 4nec2 tool

I am trying to find near field mutual coupling affects between two antennas - one being transmitter and other being receiver. The receing antenna is fed with very little voltage (I think, if I don't ...
7
votes
2answers
321 views

Center frequency spike on software radio for mismatched/disconnected antenna

A while ago I was using a software radio receiver to perform some antenna analysis. I left the spectrum display on while disconnecting the cable and noticed that when the cable was disconnected I ...
7
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1answer
4k views

How big can an antenna be before I need planning permission in the UK?

Presumably setting up a 1m high antenna in a back garden isn't going to be an issue, but setting up an 80m high antenna would likely cause complaints! How high an antenna can I legally construct in ...
6
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5answers
4k views

Does mounting a ground plane antenna upside down change the takeoff angle?

A typical gain pattern for a quarter wave ground plane antenna is: Image from a similar question and see watermark. For a situation where the signals of interest are below the antenna in elevation (...
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8answers
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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 ...
6
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4answers
813 views

Is there any downside to consolidating on BNC connectors for HF?

I'm new to ham and quickly finding that the new and old equipment I'm accumulating at an alarming rate has an equally alarming array of connectors: UHF PL-259 BNC SMA Type N Is there any downside to ...
6
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4answers
536 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 ...
6
votes
2answers
243 views

75 watts and a mag mount antenna

I am planning to get a Yaesu FT2900R 2 meter rig for my 2001 Honda Accord. With my 5w FT60, I wasn't able to reach repeaters that were any more than 10 miles distant (I live among mountains.) How ...
6
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2answers
644 views

Antenna length in relation to lambda length

I'm pretty new with antenna stuff. I'm not sure how to understand antenna length in relation to lambda with dipole antennas. If a simple dipole antenna is lambda/4, has it a total length of lambda/2 (...
6
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2answers
4k 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....
6
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4answers
6k views

Does oxidation of the antenna elements have any impact on the signal quality of the station?

So I'm still QRT; apart from a brown-out on the rig, the support on the inverted-vee toppled over in high winds. Thanks to the topple-over I discovered the conductors (SWG 16 bare copper) had ...
6
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1answer
8k views

How to find the front-to-back ratio given an antenna radiation pattern diagram?

I know that the front-to-back ratio is 18dB in the below antenna radiation pattern diagram, but I don't know how to read the diagram to obtain this result. How does one read and understand such ...
6
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4answers
326 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, (...
6
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7answers
143 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 ...
6
votes
2answers
474 views

How to determine if my antenna is an effective radiator?

So I build an antenna, tune it with the SWR and make it look great for a 50 ohm load. That does not determine if it is good at getting a signal out or not, it could just be a 50 ohm dummy load. ...
6
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6answers
5k 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 ...
6
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1answer
294 views

1280 MHz propagation out of a mountain valley

I live in a small valley, surrounded on three sides by 200-300 foot ridges. I'm trying to figure out where to place an antenna mast to receive 1280 MHz video from a long range aerial vehicle (20-...
6
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4answers
895 views

Why a thousand miles long antenna is not needed to receive LW and MW?

From what I've learnt so far, the longer the wave frequency on which you want to transmit or receive, the longer the antenna needed to do so. However my portable receiver other than SW can also ...
6
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5answers
9k 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 ...
6
votes
1answer
243 views

Why do some antennas list modulation type alongside power rating?

Looking at HF antennas I've noticed that occasionally I'll see power ratings similar to "200W (SSB)". Why would the modulation matter for an antenna's power output rating, and in the absence of other ...
6
votes
1answer
121 views

How to ground with little surface area?

Let's say I have a very small device, like an RC airplane, which transmits information as well as receiving commands for control. The body is made out of non-conductive foam, therefore not much ground ...
6
votes
3answers
7k views

How can I construct a practical loop antenna for 2m band?

How can I construct a practical loop antenna for 2m band to use in a fox hunt? Is it even possible to construct a hand-held antenna for the 2m and 70 cm bands? I tried to calculate the dimensions ...
6
votes
2answers
582 views

Multiband vertical antenna not working as expected

I built a vertical out of a 5M aluminium pipe. It tunes fine (and wide!) on 20M. I decided to add a loading coil to operate it on 40M, and it also worked fine, albeit not so wide. While I was at it, I ...
6
votes
1answer
1k views

RX antenna and RTL SDR with upconverter ..How to hear something?

I mounted a small RX antenna (mini whip, bought from eBay) (on 10-th floor) and I want to try to listen to something. I bought a RTL-SDR with Upconverter which supports HF. RX antenna's operating ...
6
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3answers
761 views

2.4 GHz Antenna for RC copter

What is the best omni-directional antenna design for any RC flying objects? Many times I've lost signal and my copter falls due to lost signal. (Using default antenna). Since the receiver and ...
6
votes
2answers
118 views

distance between shack and antenna

I am putting a 40m antenna in my attic and I was wondering would it be safe to have a shack in the room right below the attic (10ft of coax or less) or should I have my shack in the basement/ground ...
6
votes
3answers
233 views

Will an iron chimney work well as an antenna?

There is an iron chimney near my house that is not used anymore. It is ~15 meters in length and ~0.5 meter in diameter. How good will it be as an antenna for rtl-sdr?
6
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3answers
2k views

Will coaxial cable degrade over time?

I have a 40' section of RG-8 that is about 35 years old. One end was terminated with a standard PL-259 and the other was soldered directly to an antenna. When I removed the connector from the one ...
6
votes
2answers
442 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 ...
6
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2answers
2k views

DIY lightning arrestor - gap size?

I have an antenna that's well above the treeline, and I've heard I can add some small amount of protection by placing two bolt heads a short distance from each other, one connected to the antenna, the ...
6
votes
1answer
10k views

How to determine antenna height for given HF frequency and coverage radius?

I'm planning on setting up a low-HF antenna for near to mid-range contacts. In my particular case, ideally I would like to be able to cover a radius of approximately 1000-1200 km with good ...
6
votes
2answers
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?
6
votes
1answer
412 views

What kind of antenna is this?

This was found among some old ham stuff and is believed to have been used on 2 meters. The vertical elements are 17 1/2" long and the connector on the bottom is a standard SO-239. Antenna (left) and ...
6
votes
1answer
288 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,...
6
votes
2answers
105 views

Effective Area of Dipole Array

I'm trying to design a low frequency dipole interferometer antenna array. I am realizing how little I know about radio antennae. I'm confused by the concept of effective area $A_e$ and how it applies ...
6
votes
1answer
142 views

Why does adding 50-ohm BNC Ethernet terminator(s) in parallel to my 4-element yagi improve my radio's reception? (70cm)

I have this radio, with a rubber duck antenna, and a repeater twenty miles away to my north-northwest. If I set my radio on the top of a cabinet in my bathroom, I receive the repeater fine. I can't ...
6
votes
1answer
685 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 ...
6
votes
1answer
993 views

Are there easier ways to make traps than coax and plastic pipe?

I recently built an antenna for my attic inspired by http://degood.org/coaxtrap/. I found making the coax traps very time consuming and frustrating to tune. I got to thinking about 3D printers, and ...
5
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3answers
537 views

Cheap antenna for new HF HAM

I just got a 100W HF radio and I am new at this. What is the cheapest antenna I can hook up without burning up my radio or shocking myself?
5
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2answers
345 views

Share wide band antenna with multiple transceivers

I'm trying to incorporate several transceivers on my board design; I need WiFi (2.4 GHz) SatCom (~1.6 GHz) RF (~900 MHz) and GNSS (~1.5 GHz). I need to combine them into one antenna. I found a wide ...
5
votes
4answers
490 views

TV strong station has no signal when coax is connected

Right, not directly ham radio related, but this puzzles my ham brain. I have several TVs connected to a distribution amp connected to an outside antenna. All but one work fine, and the one won't ...
5
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2answers
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?
5
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4answers
1k views

Efficiency of short dipole receiving antenna

For a transmitting dipole antenna, its length is important. If it is close to half the wavelength, it will be efficient and most of the input power will be radiated. How important is the length of ...
5
votes
3answers
293 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?

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