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Questions tagged [dipole]

Use this tag for questions relating to dipole antennas.

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0 votes
1 answer
44 views

Natural dipole / monopole filtering

Word has it these antennas are broadband, however my calculations show one may not need FM / AM BCB wave traps if not operating around those frequencies. I have run the script here for: ...
0 votes
1 answer
90 views

Converting a 470-694Mhz TV antenna for 433Mhz reception

I'm working on a project which requires me to pick up LoRa signals that will be transmitted from a relatively low gain antenna. I've figured out that a large dipole would be idea for the receiver ...
0 votes
2 answers
78 views

How is the length of an inverted V affected by being too close to the ground?

In the near future, I'm planning to build an indoor inverted V dipole. However, I won't be able to raise the ends significantly above the floor. I understand that this will adversely affect ...
0 votes
1 answer
124 views

Input impedance of a shortened dipole antenna

I want to make myself a antenna for 40m and 20m wavelength band, but i don't have enough space for a full scale dipole, and even for more compact configurations like delta-loop or inverted v, so i ...
2 votes
1 answer
97 views

Insulated mounting pole section for vertical dipole?

I am considering improving my 2m vertical dipole by replacing the top section of mounting pole with non-conducting tube. Will this have a positive effect on gain? I am theorising that the downward ...
0 votes
2 answers
127 views

How to determine the best length for a short dipole antenna

If I were to design a dipole antenna that's significantly shorter than usual for the frequency, how can I determine the best length to use? In other words, given a frequency and a maximum length (...
6 votes
3 answers
1k views

Correct number of elements in 4nec2 antenna simulation

I am designing a 1.25-wavelength dipole antenna with the 4nec2 software. What I noticed is that the input impedance of antenna is changing greatly when I change the number of segments. How many ...
2 votes
4 answers
176 views

Wave bounce inside a resonant antenna

Let's assume we have a transmitter, a feed line, and a standing wave antenna (dipole, etc.). The transmitter is matched with the feed line, and the feed line is matched with the antenna, which is why ...
3 votes
3 answers
336 views

Advice on constructing half wave dipole with reduced velocity factor for site that is not quite big enough?

I want to construct an antenna competent on the 160m band, but I haven't got quite enough space, here's my thinking, please let me know if/what you agree/disagree with. I have a plot of land with ...
2 votes
4 answers
4k views

Turn 75 Ω TV "Rabbit Ears" with a balun into a 50 Ω dipole antenna

I got myself a TV "Rabbit Ears" module originally for a TV. It came with a small length of coax, permanently attached to the antenna foot, and a Belling-Lee connector on the other end. My idea was to ...
0 votes
2 answers
143 views

Is the phase difference between the voltage and current of the standing wave on a dipole antenna constant along the dipole's length?

Everyone knows that a 1/2 λ dipole antenna has on it a standing wave of RF energy the voltage and current of which are about 90° out of phase with each other. The standing wave is circulating reactive ...
1 vote
2 answers
183 views

How is it possible for a halfwave dipole antenna to be resonant?

I've been learning about antennas recently and I have some questions about the halfwave dipole antenna. My first question is about its resonance; as I understand it everything that oscillates has a ...
1 vote
2 answers
197 views

What antenna is in this cylindrical vertical omni

Recently, I have received an antenna from one of the Chinese manufacturers and they haven't disclosed the detailed specification. Below is the picture of my antenna (please ignore the specification in ...
9 votes
6 answers
25k views

How is a 1:1 current balun different from a choke?

I have a 10m dipole and am going to feed it with 50 ohm unbalanced feed line (coax). My understanding is the feed point of this style antenna is about 50-75 ohms, and since it is a balanced antenna I'...
0 votes
2 answers
265 views

1/2 wave dipole instead of 1/4 wave + ground plane

I have a transceiver operating at 150MHz using a 1/4 wave vertical whip and horizontal ground plane at 90 degrees. My end user doesn't like the antenna sticking up in the air (trip hazard) so I'm ...
1 vote
3 answers
1k views

Why does SWR of a dipole decrease the closer it is to the ground?

I experimented with a 20m dipole made of a 1:1 balun connected to 2x ~5-meter lengths of copper wire, running parallel to the ground (by "ground" I mean "pavement", not quite the ...
1 vote
3 answers
125 views

Tips for getting a 2m dipole higher while out in the field

I want to start operating the 2m band while camping, but with my current setup, my antenna would be very close to the ground and ineffective. So I'm wondering, does anyone have tips for constructing ...
1 vote
1 answer
207 views

How to splice a 12 gauge, stranded wire to a ladder-line stranded wire?

I am building a zs6bkw dipole using a ladder-lock. For mechanical strength, I am looping the 12 gauge wire, as in the image below, and swaging it. The next step is to join the thick antenna wire to ...
3 votes
2 answers
220 views

What kind of crimp part is used for stress relief on dipole?

I like the way that the person provides stress relief for the dipole antenna wire in the following image. However, I cannot figure out what kind of crimp "device" they are using for making ...
2 votes
0 answers
150 views

How to convert device with Monopole antenna to Directional/Dipole antenna?

I'm trying to increase the transmission range of a stationary wireless microphone toward its receiver by connecting a yagi antenna. Aside from the antenna sticking out of the top, I don't know where ...
4 votes
1 answer
194 views

Chimney Flashing Affect on Dipole Antenna Resonance

I put up a 40m dipole off a metal mast attached to a chimney mount on a 25' roofline. The chimney has metal flashing on the top with a metal spark arrest dome on top. I have 125' of RG8X feeding an ...
19 votes
5 answers
16k views

Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?

This is something I've read in passing, but never encountered an explanation of why. For example, Wikipedia says: Another common place one can see dipoles is as antennas for the FM band; these are ...
5 votes
2 answers
312 views

What happens if I “open” a folded dipole so that the two wires are not connected anymore?

A folded half wave dipole consists of two wires in parallel with only one of the wires driven, but the ends of the two wires electrically connected. As I understand it (and I may well be wrong there) ...
4 votes
1 answer
920 views

How does the material of a fishing-pole mast affect antenna performance?

I'm a newly-licenced ham and currently starting out with HF. My home doesn't allow for a permanent setup. I can therefore only operate portable from parks and such, with limited TX power (my rig goes ...
1 vote
2 answers
592 views

For a resonant half wave dipole, is the phase of the applied RF voltage at the feedpoint in phase with the current reflected from the ends?

For a resonant half wave dipole, the voltage and current of the standing waves on the antenna are 90 degrees out of phase with each other. At resonance, is the phase of the current reflected back from ...
1 vote
2 answers
213 views

How Does the Propagation of H-pol E-M Fields Compare to That of V-pol E-M Fields (other things equal)?

A rather popular belief on this topic is that h-pol is superior to v-pol. Probably that is traceable to published "far-field" patterns over a lossy ground plane generated by Method of ...
2 votes
2 answers
145 views

Can I convert an inline 1:1 CMC into a balun feed for a dipole?

I built my first 1:1 CMC transformer recently using 100 ohm CAT5e pairs in parallel. I used an FT-114-43 with 9 turns on each side and squeezed it into a small box with female coax connectors. I plan ...
13 votes
1 answer
2k 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 ...
3 votes
3 answers
827 views

Antenna options for a small urban garden

I've narrowed down my antenna options to fit a small urban garden. It's tough, space is tight and a neighbour three doors down reports everything I do to the council so I'm routinely inspected for ...
2 votes
2 answers
504 views

How bad is it to make dipole elements slightly helical?

I'm looking to make a dipole for 10 M. TX power won't be more than 10 W, likely less than 1 initially, but I would prefer that it be reasonably good performance for reception. EDIT: After a ...
5 votes
2 answers
281 views

4:1 Balun question

With an OCF dipole, does it matter which leg, short or long, is connected to which side of the 4:1 balun, hot(coax center) or shield? How can you tell which is which, the balun is not marked. Thank ...
2 votes
1 answer
691 views

What kind of wire would be good for a 160m - 40m fan dipole?

I want to know the best copper wire or tinned copper wire for a fan dipole for 160, 75, 40 meters. It would be coax fed and I would like it to handle 1500 watts or more. I would like 65/30 strands of ...
2 votes
3 answers
1k views

Why half-wave dipole is the most efficient one in comparison to other electrical lengths of that antenna?

I have a problem on the understanding of a half-wavelength antenna. Namely, why is the half-wave antenna has a highest power emission. Considering Far Field factor F($\theta$), which is known from the ...
3 votes
1 answer
257 views

Calculating SWR for a dipole

I have a dipole wire antenna that is tuned to 14.0 MHz so that it has an SWR there of nearly 1:1. Is there a mathematical formula by which I can compute the expected SWR for other frequencies? I would,...
2 votes
6 answers
1k views

For a half wave dipole antenna, what's the value of the reactances that cancel out when the antenna is resonant?

According to a few books and articles on antenna fundamentals I've read recently, including Wikipedia and the ARRL Handbook, when a half wave dipole is resonant, the inductive and capacitive ...
4 votes
5 answers
948 views

How can the impedance of a half wave dipole at its resonant frequency be purely resistive when the voltage and current are seemingly not in phase?

A half wave center-fed dipole has a resonant frequency where the input impedance appears to be purely resistive. How can this be, when the voltage and current distribution along the length of a half ...
7 votes
4 answers
1k views

How can the voltage at the center of a resonant half wave dipole be zero if the input impedance is 75 ohms?

If the input impedance of a resonant half wave dipole at the feed point is 75 + j0 ohms, then if an AC sine wave voltage V is applied to the feed point, how can the voltage at the center be zero ? ...
1 vote
2 answers
227 views

Does the self inductance and velocity factor of the elements of a dipole antenna change its resonant frequency?

Below are well known equations from Wikipedia for the resistance and reactance in the impedance of a dipole antenna. where $a$ is the radius of the conductors, $k$ is the wave number 2πf/c, $η_0$ ...
5 votes
2 answers
2k views

Dipole versus ungrounded end fed for HF RX

I've built a 2 meter ground plane antenna that works pretty well for RX and has a decent SWR on 2 meters with my Alinco. However, I'm experimenting with SDR quite a bit and would really like to build ...
5 votes
2 answers
517 views

Can coax be run through the center of a radiating element without currents being induced on the coax shield?

I run a λ/2 vertical dipole for 20M that's fed to a 1.5:1 balun at its center with coax that is perpendicular to the dipole (parallel to the ground), for about 30 feet before it comes down to the ...
8 votes
3 answers
3k views

Estimating the efficiency of a shortened (loaded) antenna

Recently I've build a trap dipole for 20/40/80m bands. I followed an article by John DeGood, NU3E and got following measurements: From balun to 20m trap: 485 cm From 20m trap to 40m trap: 362 cm From ...
5 votes
1 answer
3k views

What frequency to set trap on?

I plan to build trapped multiband dipole so I read lots of documentation I found. There is one thing that confuses me: various authors recommend setting resonant trap frequency differently: some say ...
5 votes
3 answers
1k views

When a dipole antenna is fed via coax, what powers the ground-side of the dipole?

I've been trying to understand how dipole antennas work, and I believe I understand the basics when they're fed via a balanced feed line. In fact, every dipole physics YouTube video and web page I can ...
1 vote
1 answer
305 views

Is a MagLoop antenna better than my 50ft end fed di-pole for 20-80 meters?

I'm restricted to putting antennas in my attic which is 50 feet long and peaks at about 8 feet. I'm currently using the Nelson UJM-150-50 end-fed dipole 80-10 meter antenna. The attic is about 25 feet ...
5 votes
2 answers
2k views

Receiving the ISS SSTV: dipole antenna configuration and orientation

In short I am trying to receive SSTV Images from the ISS (145.8Mhz) and I all have is a simple "bunny ears" dipole antenna. In what configuration (straight, vee shaped, upside down vee, ...) ...
4 votes
1 answer
7k views

3 Band (80-40-20 Meter) Fan Dipole Tuning Question

I built a fan dipole according to the basic instructions in the SRI publication describing the theory and basic design. My questions is about next steps in tuning for the various bands. I am ...
2 votes
1 answer
202 views

Identical HF Horizonal Dipoles Operating in Close Proximity

I'm planning to use a multiwave horizontal dipole oriented to work comms toward Alaska from Colorado. That ends up being awkwardly oriented to work east coast and Europe. If I placed a second ...
2 votes
2 answers
266 views

Destructive interference between two close antennas

let's consider this two planar biconical dipoles of total length and width each one 10mm, at a distance D = 25.6mm. They are excited with the discrete ports in the picture, which corresponds in this ...
2 votes
1 answer
97 views

Phase shifts in antenna arrays

Let's consider a simple antenna array. For instance, this three-elements equispaced dipole array: Each dipole is connected to a signal voltage source. It's well known that it's possible to choose the ...
2 votes
0 answers
93 views

Printed Dipole Transmission Line Equivalent Model

let's consider a printed dipole on a substrate with a GND plane: I've seen many times an equivalent model which uses transmission lines like this (reference): This model is useful to understand the ...