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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3
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1answer
1k views

Counterpoise from artificial ground vs base of antenna

I have an MFJ-934 tuner/artificial ground for my MFJ-1699 multi-band vertical (stuck on a balcony, so limited HF antenna options), and I'm wondering if there's any downside to the counterpoise ...
10
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4answers
892 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 ...
2
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3answers
4k views

How does the antenna length affect signal transmission/receipt in different bands?

My Canadian Amateur Radio Basic Qualification Study Guide tells me that my antenna length is specific to the wavelength I wish to broadcast on and gives a formula that equates to antenna length = half ...
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....
10
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1answer
4k views

How to design a rubber ducky antenna

I am attempting to design an antenna for a 162.4 MHz omni receive only application and am confident it is going to be difficult if not impossible. I have very tight specs on space(6" diameter by 3" ...
8
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1answer
3k 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 ...
1
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3answers
470 views

Copper Wire connecting log periodic elements to boom

Should I or should I not replace an aluminum wire (defective) with a copper wire on a Hy-Gain LP-1010 log periodic ham radio antenna which is made entirely of aluminum with stainless fasteners? There ...
7
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1answer
3k views

How far does an antenna need to be from metal to avoid problems?

Living in an apartment, I'm struggling to get good antennas set up, especially for HF. Worse yet, I'm not allowed external antennas (but am willing to try something low profile on the balcony), my ...
8
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1answer
477 views

Why must twin-lead conductor spacing be small to avoid radiation?

A transmission line does not radiate when the spacing between the two wires is very small when compared to the wavelength, but the transmission line begins to radiate when the spacing between the ...
5
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2answers
140 views

How is RF a radio receives just not a mishmash of eletromagnetic energy?

So at any given time, electromagnetic waves of many different frequencies are flooding the space around me. I have a little 2 meter radio. Are not all these electromagnetic waves exciting the ...
11
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4answers
1k views

Are antennas circuits?

For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit? If they are not circuits, then how ...
8
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4answers
3k views

What's the difference between “minimum SWR” and “resonance”?

Is the point of minimum SWR equivalent to resonance? Exactly what does resonance mean, anyway?
3
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1answer
227 views

Is it possible to make a shield that blocks time-varying electric fields, but not time-varying magnetic fields?

Take, for example, a shielded loop antenna. It is often claimed that the antenna is inside the shield, and the shield blocks electric fields from reaching the antenna, while allowing magnetic fields ...
3
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2answers
305 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 ...
2
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2answers
1k views

Best mobile antenna for the mountains

For two meters, a 5/8th wave antenna has the best omni gain. But I think the lobe is very low takeoff and not good for mountain work. What is best for the mountains on a mobile? Yes, I know not ...
3
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2answers
2k views

How to recieve a signal from multiple sources simultaneously (helical antenna)

I'm working on a system (theoretical at the moment) whereby I wish to receive data from multiple sources all transmitting at the same time. I've read that a helical antenna is capable of this. I'm ...
4
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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 ...
1
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2answers
661 views

Multi-part question. correct length of rg-8x coax to connect 2 meter HT to 50 ohm yagi

What it the optimal number of wave lengths of RG-8X coax to connect my Icom IC V80 HT to a 50 ohm Jetstream JTBM270 Yagi (3 elements 2m/5 elements 70cm)? Odd or even number thereof? Will running the ...
4
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4answers
985 views

Counterpoise for telescopic antenna AL-800 as a portable/base antenna on 70cm?

Recently I bought a telescopic antenna, model AL-800: http://www.pryme.com/index.php?l=product_detail&p=2155 It is 863mm (34 inches) long when fully extended. When retracted, it is 785mm long. ...
2
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2answers
143 views

Reciprocity and SWR [duplicate]

If someone has a high SWR, obviously their signal will not make it out as far due to reflections. However, they will still be able to hear relatively well. I have noticed for receive, a high SWR may ...
1
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2answers
298 views

Antenna + LNA Design Questions

I am trying to design and build an antenna + LNA board. Antenna: http://www.yageo.com/documents/recent/An_FR4_1690_2405_0.pdf LNA: http://www.avagotech.com/docs/AV02-1237EN The antenna is specced ...
5
votes
4answers
1k views

Can my small ham radio antenna interfere with WiFi in my RV park?

We live full time in our RV. We are at an RV park for the winter. They just knocked on my door and asked what kind of antenna I have on top of my RV. I told them it's a small ham radio antenna that I ...
5
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3answers
689 views

Is possible to make small HF microstrip or helical antenna by using high permittivity dielectric material?

Is possible to make small HF microstrip or helical antenna by using high permittivity dielectric material like SrTiO3 ?
5
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1answer
2k views

maximum acheivable range on CB radio by ground wave? [duplicate]

I have 10 watt CB radio system & 0.64 lambda monopole antenna , I think it has a 5 dBi gain . what is the maximum acheivable range by ground wave in an urban area ? If I want to increase my ...
3
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1answer
82 views

How much distortion would aluminium wire stays for the centre-pole on my inverted-vee cause?

I used nylon rope from the nearest hardware store to stay the centre-mast on my inverted-vee for the 20. The centre-pole is a long long looong bamboo. The trouble is rain here really isn't friendly to ...
2
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2answers
868 views

High data rate on HF & MF bands

Is it possible to transfer data at a high rate, like 1-2 Mbps, on 0.5 - 30 MHz? From Shannon's Theorem, with a bandwidth of just 300 kHz it is possible to reach 1.5 Mbps. I want to use these bands ...
2
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1answer
111 views

How can I render my 2.4GHz antenna directional?

With barely no knowledge in this field, I would like to render my antenna used with Bluetooth BLE devices more directional. I tried to shield the antenna with different kind of metals with no luck. ...
7
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2answers
307 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 ...
2
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3answers
966 views

How to shorten the length 50 ohm characteritic impedance antenna cable

I have two 50 ohm characteristic impedance cables of which I need to shorten their length to compact my design. (put everything in to a box) The cables I need to shorten are the GPS & GSM antenna ...
3
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1answer
570 views

Idea for better reception in crowded city

I am living in crowed area of a city. It is impossible for me to set up an antenna outside the apartment. I receive signal inside the room. I have a funcube dongle pro+ and some RTLSDR, the picture ...
4
votes
2answers
201 views

Antenna Design for specific directions

I am designing an antenna for a device and was hoping to gain some insight in the correct design direction for the antenna. The Idea: A receiver & antenna that fits in a 6" diameter by 3" deep ...
5
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1answer
233 views

What is a general procedure for aligning directional antennas?

I want to establish a microwave link (1.2GHz) between two stations using antennas with a directional radiation pattern. The stations have a clear line of sight to each other. Each antenna is attached ...
6
votes
3answers
737 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
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5answers
8k 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 ...
1
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1answer
135 views

Magnum 257 & Firestik 3' Tuning

Trying to tune a Firestik antenna connected to Magnum 257 on my '98 Jeep Wrangler. Having trouble with SWR reading as it is reading too high (~4) after I set needle on FWD and then switch back to REF. ...
1
vote
1answer
441 views

In which direction should single wire antenna in underground parking be pointed?

In our collective building lot we have an underground parking, in which a company recently changed a functional garage door system, since then the reception is a lot worse than before. (Like it doesn'...
0
votes
1answer
97 views

If the desired frequency is known, can an antenna tuner tune its 'x' different dimensions sequentially for maximum gain?

Assume I have rotators that are able to move an antenna in different dimensions. For example, on the x, y, and z axis. I want to automatically move the antenna to its optimal physical orientation, ...
2
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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 ...
3
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2answers
2k views

Adequate lightning protection for sloped dipole or G5RV?

Has anyone had experience, or knows from first principles, whether installing a G5RV or dipole BELOW a "lightning-rod" in such a manner would serve as a means of discouraging direct lightning strikes ...
5
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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 ...
2
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1answer
1k views

What are the effects on an ATAS-120A screwdriver antenna with a limited ground plane?

I'm going to be installing an ATAS-120A screwdriver antenna at the corner of a metal roof building, without radials going out over 270 degrees of the plane it's on. Will this significantly change the ...
4
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2answers
3k views

Can I ignore the radial elements of a 2m/70cm antenna if it's on a metal roof?

I'm looking for a dual band base station antenna, and find that many of them have short radials around the base. Due to the specifics of my installation, I need to remove them. However, it is being ...
2
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2answers
596 views

Why isn't the mast an antenna?

A lot of "big antenna" pictures show these very tall masts being used to hold up a variety of other HF antennas. The mast itself is almost always conductive, though, and I'm wondering why they aren't ...
0
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8answers
604 views

Explain how an antenna works to an 18 year old

It's either math or magic. It seems like the only thing that will explain operation are complex formulas. If a child were to ask "how does an antenna work" what should one say, it magically changes ...
6
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2answers
387 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. ...
4
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1answer
1k views

Does a larger Biquad antenna give better results?

Consider a biquad antenna used for receiving, not for sending. They are typically built with each side having a length of $\lambda / 4$. If a biquad antenna was built with a side length of $\lambda / ...
8
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2answers
3k views

How does a Dual Band Handheld Antenna work?

Looking to get a (highly recommended) NAGOYA NA-771 37cm "Dual band (2M/70cm) handheld antenna" for my Baofeng UV-5R. If my math is correct - this is about a half-wavelength antenna for 70cm, but ...
3
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2answers
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 ...
8
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3answers
2k views

What sort of radiation efficiency can one expect from a folded dipole?

It is pretty well established that folded dipoles have much greater acceptable-SWR bandwidth than ordinary dipoles. Radiation efficiency is simply the quotient of radiated power to the antenna ...
3
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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 ...