# Questions tagged [dipole]

Use this tag for questions relating to dipole antennas.

115 questions
Filter by
Sorted by
Tagged with
587 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 ...
177 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 ...
632 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 ...
924 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 ? ...
44 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 ...
42 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 ...
100 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, $η_0$ ...
1k 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 ...
305 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 ...
1k 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 ...
2k 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 ...
140 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 ...
105 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 ...
89 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 ...
15k 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'...
423 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, ...) ...
3k 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 ...
59 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 ...
78 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 ...
57 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 ...
44 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 ...
3k views

### Balun and tuner configuration for multiband dipole

I'm putting up a multiband dipole in some tall trees. (Perhaps it's more correct to call it a "dipole-doublet"). The situation I'm imagining looks like this: The legs of the antenna are each 100 ...
262 views

### Exactly what is the cause for the zero reactance seen in the impedance at the center feed point of a resonant half wave dipole?

Lots of explanations i've read on the internet written by ham radio operators and in some text books state that a half wave dipole is resonant when the inductive and capacitive reactances cancel out. ...
37k views

### What is a Gamma match in the context of the driven element of a Yagi antenna?

How (and why) does a Gamma match work, when used on the driven element of a Yagi antenna? As shown here: (source: http://www.iw5edi.com/ham-radio/?2-element-yagi-for-10-meters-band,49) The article ...
41 views

### How to decide between Dipole and Monopole antenna for Cubesat Uplink (433 MHz)? [duplicate]

We are currently deciding between a dipole and a monopole for uplink (435MHz) , while the monopole is easier to feed, we are unsure of how effectively we'll be able to implement the ground plane, ...
101 views

### Half wave dipole with parasitic element, (Gain calculation)

good morning all, I have difficulties to find the correct formula that allows me to calculate the gain of half wave dipole in parallel with another parasitic half wave dipole. I'm trying to calculate ...
6k views

### Grounding a dipole

How do you properly ground a dipole (RX only for VHF scanning) to protect it against ESD/lightning? In my set up i'm putting a dipole on my roof. I've connected the two dipole elements together with ...
252 views

### How does a 40/15m dipole with capacitance hats work?

I followed an article Antenna Here is a Dipole [PDF] by James Hearly, NJ2L to build a dual band 40/15m dipole: The antenna works more or less as expected. My 40m dipole was resonant at 7.030 MHz and ...
1k views

### How to increase the bandwidth of half-wave dipole antenna?

I have designed a half-wave dipole antenna for frequency range of 150 to 200 MHz. Due to resonant frequency of 175 MHz, Its dimensions are: L=817.44 mm, R=1.71 mm. Impedance is also equal to 73 ohms. ...
137 views

### Yagi performing far worse than a dipole

A few months ago, I built a 6 element yagi: 3 driven elements, and 3 reflectors. For 10-15-20m. I was able to tune it to SWR 1:1 for the FT8 frequencies in each band. This antenna is only 6m above ...
164 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 ...
249 views

### How Does the Performance of an Inverted V Dipole Compare to a Linear Dipole?

The NEC4.2 comparison in the answer below shows one example, for a practical set of installation conditions.
101 views

### Built a 2 meter 5 element Yagi

Straight dipoles. I can't get the Yagi to tune. I have tried the 4:1 Balun method with coax but not able to tune. With the straight unbalanced input to the dipole I get a 1:1 swr on about 129 MHz ...
176 views

### Pondering variations on the vertical bazooka antenna

I've seen these antennas built out of coax that are called a bazooka vertical. It's a kind of 1/4 wave vertical, or perhaps a 1/2 wave dipole. Constructing such an antenna is to roll back the outer ...
376 views

### 440MHz collinear dipole array - suitable coax?

friends! Finally found my next antenna project..a collinear dipole array for the 70cm US ham band. The general idea: (image courtesy https://link.springer.com/referenceworkentry/10.1007%2F978-981-...
204 views

### What is an expected SWR plot for a trap dipole?

I've build a trap dipole for 20/40m bands. Traps are made of a coil wound on an insulator of RG213 coax and 3 kV NP0 capacitors. The impedance measured with EU1KY antenna analyzer is following: This ...
2k views

### Can a 1:1 transformer be used as a protection from static electricity?

It's well-known that under certain conditions verticals and dipoles can gather static charge, which is a common reason of transceiver damage. There are several ways to solve this issue. Some hams ...
151 views

### What is the impedance of an off-center fed resonant dipole?

Given a dipole approximately 0.48 wavelengths long, such that when fed in the center the feedpoint impedance has zero reactance, how does the complex impedance change as the feedpoint is moved away ...
698 views

### How to calculate power transmitted by monopoles?

I only studied monopole in sending mode or receiving mode alone but never in both modes together, I have this question which says: Two vertical λ/4 monopoles are parallel to each other with 20 ...
14k 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 ...
2k 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 ...
719 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 ...
121 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 ...
117 views

### How should I stack these folded dipoles?

Looking to stack these 8 folded dipoles on my 100ft tower. I can not find any information whatsoever on these. I have 4 consecutive serial numbered boxes. Bluewave Marathon BME139FN1H0 138 - ...
96 views

### 40 meter band Dipole antenna designed is not receiving any signal at 2 km distance

I am using a Pixie transceiver, giving 1 W power and 7 MHz frequency. A 40-meter band dipole antenna, providing 5 dBi gain at high angles, has been designed and connected at the output of the circuit ...
66 views

### What is the effect of coil Q on a shortened dipole?

I made a small yagi, with the driven element being a coil loaded dipole. What is the effect of coil Q in this situation? The coils I built are 18 turns of 1.2mm enameled wire wound tightly with a ...
918 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 ...
404 views

### To folded dipole, or not to folded dipole?

I currently operate a 20M half-wave dipole with a balun. It's a little lower than ideal, but it gets me on the air. I've read about folded dipoles. But I've found contradicting information about them....