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
8answers
8k views

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 ...
3
votes
2answers
3k views

Choosing a wideband antenna design

On a previous question I asked about proper antenna design for wideband SDR receiver and ways to improve signal/noise ratio. Ideally the reciever has a range of 100kHz-2GHz. Keeping in mind is ...
17
votes
3answers
2k views

What is a “random wire antenna”?

Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system? From everything I have heard, the resonance of the antenna (...
12
votes
6answers
23k views

Calculating Antenna Length on the FCC Exam vs. in Reality

I have seen the following formulas for calculating half and quarter wavelength antennas: Formula for $\frac{1}{2}$-wavelength antenna (in free space): \begin{equation} \mathrm{Length~(feet)} = \frac{...
10
votes
4answers
905 views

How does an antenna transform impedances along its length?

If I insert some impedance (like a loading coil, or a trap) at the base of a monopole antenna, the effect on the feedpoint impedance is easy to predict: the impedance is in series with the antenna, so ...
9
votes
2answers
3k views

Can every antenna be used both for transmit and receive?

Assuming I have an antenna for receiving GPS signals, can I use it also for transmit — to create a repeater in a tunnel (or some place with no reception)?
8
votes
3answers
986 views

What is the proper way to ground your station's antenna?

I don't understand how you would go about giving an RF ground to your antenna. Would it not become an additional radial and affect the signal? What is the proper way to ground your station's antenna?...
8
votes
1answer
4k views

How does a slot antenna work?

How does a so-called slot antenna work? How can one construct one? What might be the radiation pattern and efficiency compared to a wire antenna? And, if a small slot antenna "works" at mobile ...
8
votes
3answers
963 views

Vertical antenna on HF?

What are some of the advantages and disadvantages of using a vertical antenna on high frequency? Are there any better antenna types that I should use?
5
votes
3answers
15k views

How to improve reception with a headphone-cord antenna?

I have a headphone and a cellphone that has built-in FM radio, and the headphone acts as the radio antenna. but my problem is the radio stations I listen to are very far from my place, good thing ...
5
votes
1answer
1k views

How to calculate or estimate surface area of required ground plane for a mobile antenna?

I don't have conditions for installation of a fixed 2 m/70 cm antenna at home, so I'm thinking of using a mobile magnetically mounted antenna on a conductive plate instead. So my question is: What ...
4
votes
1answer
174 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
votes
1answer
241 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 ...
3
votes
6answers
3k views

Smallest HF antenna for DX?

There seem to be reports of people trying to see how far an HF DX contact can be made using the tiniest transmit power (mW or even sub-mW QRP). But many of these contacts seem to be accomplished ...
2
votes
3answers
425 views

Why long wire antenna length shouldn't be a multiple of λ/2?

Numerous sources say that LW length shouldn't be a multiple of λ/2 for any frequency in interest. This will cause the antenna to have a high impedance at this frequency. Since the coax cable impedance ...
9
votes
2answers
2k views

Are satellites Left or Right hand circularly polarized?

I'm thinking of building some helical antennas for satellite work. I want to know which way to wind them. If satellites are spinning randomly, how can we know if they are left hand or right hand ...
9
votes
2answers
1k views

Why is the risk of damage to a transmitter due to a mismatched antenna at lower frequencies greater?

A quick follow-up to this answer ... If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies ... I'm sorry to be so dense, but uh why is the risk ...
8
votes
3answers
6k views

Why is the electric field orthogonal to the magnetic field from an antenna?

I've read in several places that the electric field is 90 degrees orthogonal to the magnetic field, and both are orthogonal to the direction of the wave from a transmitting antenna. What causes this? ...
8
votes
1answer
285 views

SWR Measured at the Transmitter versus SWR at the Antenna

It is fairly well understood that due to transmission line losses, the SWR as measured at the transmitter will be less than the SWR at the antenna. Some of the new antenna analyzers and some vector ...
7
votes
2answers
237 views

Communications : Ground wave propagation

I was studying ground wave propagation, my book writes the lines about it without explaining it. I really do not know any explanation for these queries coming in my mind. I've Googled it, and you will ...
7
votes
1answer
351 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
4answers
1k views

Antenna options for a 10x20m property with a large metal roof?

I live in a house that sits in the middle of the city, in a lot 10x20m in size. The first 6x10m are covered by a metal roof with a rather low angle (IIRC only 50cm difference between the highest and ...
6
votes
3answers
759 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 ...
5
votes
1answer
87 views

Will stainless steel bolts work with my copper antenna?

My antenna is copper, elements and the beam. I would like to bolt them together where they cross. Would stainless bolts work? Just sweating them together lets them twist and move some in high winds.
5
votes
1answer
310 views

Dipole antenna radiation field equation

Can anybody provide me with an idealised formula that describes the radiation pattern of an omnidirectional dipole antenna? In particular I am interested in the formula that creates a plot similar to ...
5
votes
2answers
4k views

What are some good options for covert dual band vehicle antennas?

Would like to have a 50W mobile in my SUV, but I'm not allowed to have a big whip on the outside. What 2m/70cm dual band antennas are available that don't say, "Ham Radio Operator"? Are there three ...
5
votes
1answer
138 views

Can this 960 MHz CelWave fiberglass antenna be retuned for the 70cm band?

I recently inherited a CelWave fiberglass antenna pictured below. It is marked that it's for 959.9875 MHz. The model number appears to be either 339 or 359. It is 96 1/2 inches from base to tip. I ...
5
votes
1answer
667 views

What happens to the “Yo-Yo Tenna” when you coil up its ends for use on higher frequencies?

I have gathered what is basically a Yo-Yo Tenna using some Camco laundry reels and a spool of cheap speaker wire split in half (pretty much exact duplicate of this build as it turns out). I've got a ...
4
votes
2answers
1k 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
votes
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
votes
3answers
214 views

What are these antennas used for?

I noticed this antenna park in Heidmoosstrasse, Switzerland. What is it used for?
4
votes
2answers
373 views

Resistive impedance with frequency

Full disclosure, I'm a little dyslexic. Concepts that are easy to most people usually seem ambiguous to me. I also have a had time expressing myself through writ so please forgive me if this seems ...
3
votes
3answers
410 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
votes
3answers
715 views

Unexpected Resonance - Dual-Band Dipole

I tried to make a dual-band (2m/70cm) dipole this morning by following the instructions on this page: http://www.amateurradio.bz/2m-70cm_vertical_dipole_antenna.html, with the rather major significant ...
3
votes
2answers
2k views

HF SWL antenna wire? Will plain 16-Gauge copper wire work well enough?

Planning to set up a HF antenna for RX-only. However, I can't decide what kind of wire to use. I want to buy something new. My first thought is to buy a spool of 16 Gauge copper wire, but am hoping ...
3
votes
2answers
413 views

How does the antenna noise temperature vary with antenna elevation?

I'm using a 14 element cross Yagi antenna in my system. For my link budget calculations, what antenna noise temperature should I consider? How does this vary with elevation?
3
votes
1answer
1k views

recommended capacity bottom-hat clearance above metal roof

In a few days I'm expecting to mount a Cushcraft R7000 multi-band (HF) vertical antenna on top of a metal mast that will be attached to the outside wall of a large metal shed. The aim is to have the ...
3
votes
3answers
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 ...
2
votes
1answer
93 views

tuning trouble - 1/4 wave 8 elevated ground radials 10 meter

It is resonate for 22 Mhz haven't had any luck tuning it for 30 Mhz it is an excellent antenna I feel at the Z is 0 for 22 Mhz I have given up and think I will just buy a Imax 2000 w/ radials?? "10 ...
2
votes
5answers
669 views

Metal for antenna construction?

What do I need to consider when choosing metal for an antenna? How do I determine what thickness to use?
2
votes
2answers
1k views

Field Strength calculations with known antennas

I can receive a calibrated decibel milliwatt signal level from the output of any antenna at a given frequency. With a given antenna gain (dbi) in the direction I want to receive the signal (...
2
votes
2answers
987 views

3 way coax split / impedance match

I would like to split a coaxial feed line 3 ways, maintaining 50 Ω impedance. I know how to do this 2 ways; you use 1/4 wavelength 75 Ω coax as matching stubs. I know how to do this 4 ways; you do 2 ...
2
votes
4answers
357 views

What is the maximum and minimum of antenna gap of dipole antenna?

Consider the picture below is design of half wave length (λ) dipole antenna. I read some explanations saying that it is the best design to get the optimum transmit power. Half wave length (λ) is from ...
2
votes
1answer
450 views

Will these wires affect antenna performance negitavely?

We moved into a new house, and I noticed these wires sticking up for some sort of tent thing for shade. •I tested the wires to the 3rd prong in the outlet, and it showed a DC dead short to ground. •...
2
votes
2answers
384 views

Replace directional antenna by fixed antenna

Given the following specs of a directional antenna: ...
2
votes
1answer
1k views

How much loss for 1 to 1.5 inch Coil (rubber ducky) Antenna at 70cm band?

1What is the likely antenna loss for this (coil hidden inside rubber ducky) 1 to 1.5 inches coil antenna, when placed vertically over 4 to 6 inches each side square ground plane as compare with a ...
1
vote
2answers
2k views

How to make a loop antenna for HF?

While researching this answer, I came across information that indicates that a many good Low Frequency/ Very Low Frequency antennas are loops, with high directionality and good overall characteristics....
1
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0answers
100 views

Antenna Impedance calculation for low frequency [duplicate]

If I have an end fed long wire in free space, say 100 ft, how do I calculate its $R$ & $X$ at different frequencies?
1
vote
0answers
63 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 ...
1
vote
1answer
84 views

Is this antenna “system” really work? [closed]

I posted yesterday asking how can I have signal inside my house which my house is obstructed by a hill from direct signal from the cellular's operator' Base Transceiver System (BTS). The schema of the ...