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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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 ...
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 ...
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 ...
9
votes
2answers
1k views

How might one realize a first order, two dimensional RF field antenna for HF?

I just coined the term "field antenna". It is by analogy to the lightfield camera or the soundfield microphone. Essentially, it is an antenna that captures not only the strength of an RF field, but ...
1
vote
2answers
125 views

Will swapping receiver polarity on a spiral antenna change right hand to left hand polarization?

I'm evaluating a helix antenna, and wanted to try out a reverse circular polarization than it's designed for. I do know that it's balanced and has no other components that would preclude polarity ...
3
votes
1answer
589 views

Why are loop antennas placed horizontally in HF

I am thinking of a large (circumference $\approx \lambda$) loop antenna at low (HF) frequencies. At higher frequencies the loops are used as quad antennas that have relatively high gain towards the ...
7
votes
1answer
328 views

Variable phase antenna

I'm thinking about phased antenna arrays, and am wondering if it's possible to have three fixed position antennas, and vary the length of their individual feedlines to the common point through ...
6
votes
1answer
209 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 ...
2
votes
3answers
2k views

Choke at antenna and feedpoint?

I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I ...
9
votes
3answers
5k views

What is the electrical shock risk of an antenna?

I've seen people refer to avoiding touching an antenna or bare transmission line that might be transmitting. What voltage potentials and currents are commonly found on typical ham radio antennas? Do ...
7
votes
1answer
301 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
votes
1answer
544 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 ...
10
votes
2answers
2k views

Buddipole model comparison

Can anyone give me some insight into the different Buddipole models available? They look pretty similar to me except for the sizes. What would make you choose one over the other?
5
votes
1answer
9k 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 ...
3
votes
1answer
489 views

Are there any antennas I shouldn't use in my car?

I've heard that "rubber duck" antennas shouldn't be used inside an automobile. What is the reason for this, and are there any other types of antennas that shouldn't be used inside a vehicle? From ...
8
votes
2answers
2k views

What determines power handling capacity of an antenna?

I just bought a cheap 1/4-wavelength, 2m. mag-mount antenna. The package says it can handle 50 watts. I can think of three things that could limit the capacity: $I^2R$ losses in the connection to the ...
6
votes
1answer
7k 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 ...
2
votes
2answers
124 views

What simple method will measure decoupling betwen two antennas?

I have 2 antennas which are quite close to each other. I would like to have at least a rough idea of the decoupling between those 2 antennas. I do not own a network analyzer. I was thinking of using ...
7
votes
2answers
1k 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 ...
2
votes
2answers
341 views

Horizontal dipole for a 80 foot span?

I have the K1JEK Cobra UltraLite and it works exceptionally well. However that was when I had a larger yard. Moved to a house with a smaller lot and now can't use the JEK Cobra (max span between trees ...
6
votes
2answers
226 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 ...
8
votes
4answers
10k views

How to improve VHF/UHF Baofeng UV-82 HT reception in vehicle

I have a Baofeng UV-82 dual-band (2m/70cm) HT with an SMA male connector for the stock "rubber-ducky" antenna. I would like to use it in my vehicle. I would like a high-quality magnetic mount dual-...
5
votes
1answer
317 views

How do I determine antenna spacing?

How do I determine antenna spacing so that I don't end up overdriving the front end of a receiver when transmitting?
5
votes
1answer
900 views

How to calculate power loss between radio and antenna

I have a 5W HT that only kicks out about 1W by the time it hits my antenna (which I understand is the norm). How do I go about calculating power loss in various equipment?
2
votes
1answer
741 views

What antenna to use for medium frequencies in an apartment building?

I'm living at the 6th's and top floor of an apartment building. I have a balcony with a metal balustrade. Above the balcony there is a metal roof rail. I need an antenna which won't be noticed by the ...
7
votes
1answer
3k 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 ...
3
votes
2answers
8k views

Antennas I can effectively use in an apartment? [closed]

What are some antenna designs that balance manageable size/shape with effectiveness for use in an apartment?