Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
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1answer
16 views
G5RV Jr. fed with ladder line and coax
I am a new ham and I was just given a G5RV Jr. I have about 20 feet of coax plus about 60 feet of 450 ohm ladder line I can feed it with. Can I extend the G5RV Jr. feed line with the ladder line I ...
1
vote
2answers
43 views
vertical 40m antenna takeoff angle
I built a 40m vertical using the W8AMZ design https://www.amateurradiosupplies.com/v/vspfiles/assets/images/40m_vertical_monopole_-_manual.pdf
Seems to be working for the most part. But I'm not sure ...
1
vote
2answers
68 views
True near field distance for a short monopole antenna?
Antenna properties:
Height x Diameter = 3.3 inches x 1.4 inches
Test Frequency: 900 MHz
(Wavelength = 33 cm or 13 inches)
I see some conflicting formulas to calculate the near field distance for ...
5
votes
4answers
223 views
Why does not a bigger antenna receive more power?
According to http://www.antenna-theory.com/basics/aperture.php, the power received by an antenna depends on the power density of the incoming wave, the wave length (which I consider to be fixed) and ...
2
votes
1answer
142 views
CB Radio Ground Plane (or lack thereof)
Notice the vertical antenna on the truck. I believe this first antenna is referred to as a "dipole", mounted vertically. CB to coax, coax to antenna.
The shell of the truck is fiberglass. Even the ...
2
votes
1answer
107 views
What type of this antenna is it?
Could you please tell me which kind of this antenna is? I supposed it is a modified dipole, but not quite sure. Is there any available equation for calculating the original dimensions of this type of ...
6
votes
1answer
48 views
Two antennas on different sides of a building
I live in the 4th floor of a building with one side facing south and the other north. I am able to use my 2M mobile base transceiver with a mobile magnet mount antenna placed just outside the window. ...
-2
votes
1answer
96 views
How do I understand this figure about antenna pattern? [closed]
Why the back lobes have such a large area??? I think it may be like https://www.cisco.com/c/dam/en/us/products/collateral/wireless/aironet-antennas-accessories/prod_white_paper0900aecd806a1a3e.doc/...
1
vote
1answer
44 views
Can the Q of a loop antenna be changed?
Can the Q of a loop antenna be changed?
If so what are some common techniques? (Formulae appreciated).
3
votes
1answer
44 views
Understanding of NFC Reader Antenna matching
I have been designing a 20 x 20 cm square NFC reader antenna which looks like this:
In order to make it work and detect NFC tags at certain distance, it needs to be matched. To do that I was trying ...
3
votes
1answer
82 views
Is a J-pole an appropriate antenna for mounting to a steel handrail?
Last year, a group of us placed a battery-powered 2m digipeater using a J-pole antenna on a mountaintop. We're planning on doing the same this year except we plan to use a surge arrestor from the feed ...
3
votes
1answer
70 views
Electrical Earth
I have moved to a new flat which is on the 4 floor, luckily the landlord has let me put an OCF dipole outside with coax feeding through an existing hole in the window frame. I'm looking for some ...
3
votes
1answer
56 views
Antenna Patterns and Multipath Effect
It's said that in order to decrease multi-path effects on receiving antennas that your antenna pattern should have a sharp slope near the horizon. Why?
for example this is article mentioned it.(...
4
votes
2answers
200 views
Antenna Efficiency
Intuitively, we all understand that an antenna at fractional wavelengths will not radiate well even with perfect impedance matching systems.
From what I understand the efficiency of antenna has a ...
3
votes
1answer
54 views
Skin effect - rough versus polished surface
Considering "skin effect", does the surface finish of Aluminum tubing have any practical effect on antenna efficiency at HF frequencies (5-30 MHz)?
For example: Aluminum tubing as manufactured - rough ...
4
votes
1answer
120 views
Microstrip Loop Antenna Design
I am trying to design a loop antenna for operation at 2.4 GHz, I would like for it to have above 2.5 dB gain at 2.4 GHz and have relatively good return loss (<-10 dB).
I have started my design as ...
6
votes
4answers
194 views
Why do we distinguish between balanced and unbalanced?
I hear all the time, "you need a balun between your balanced dipole and unbalanced coax to stop the common-mode current" when it seems the proper advice is "you need something to stop common-mode ...
3
votes
1answer
82 views
What is the turn spacing on a Helix Antenna?
I want to do some satellite communication so I thought why not build my own helix antenna.
I found this page:
Helix antenna design and construction details
The most things are clear except for the ...
2
votes
2answers
211 views
How do you calculate the field strength at a given distance?
Given this question from the full license exam in the UK:
What is the field strength at a distance of 7m from an antenna with an effective radiated power of 100W?
in which the answer is:
10 V/m
...
4
votes
3answers
197 views
Can an antenna be too powerful for certain receivers?
I'm brand new to shortwave radio and have been researching what kind of a receiver to get. I'll use it on the antenna I'll build (longwire, 50-100 feet) for shortwave listening; no transmitting. Right ...
3
votes
3answers
207 views
How can I calculate the 1/4-wave monopole impedance dependence on groundplane angle?
I watched this video of a very nice explanation of a simple dipole and 1/4-wave monopole. In that video they show how you can impedance match the 1/4-wave monopole by bending the 4 (virtual ground ...
2
votes
1answer
46 views
How to consider the influence from the PCB that a small antenna is mounted on?
The small antenna itself has an S11 of -3 dB around MICS band (verified with simulation and network analyzer). In application, the antenna is mounted on a transceiver PCB of 30*15*0.8 mm which has 2 ...
2
votes
1answer
152 views
Feedline and balun for 80m horizontal delta loop
I am new to HF. I'd like to put up an 80m delta loop. Due to aesthetic considerations I need to use coax to the shack. If tuned for 3.55MHz, I anticipate having a good SWR on 80m, 40m, and 20m. The ...
3
votes
2answers
121 views
How low can a vertical dipole be mounted?
An answer to this question suggests that raising a vertical dipole sufficiently can create the effect of a phased array. How about the opposite.
How low can a vertical dipole be mounted?
Can a ...
3
votes
2answers
75 views
What is the easiest way to eliminate a beam antenna's backward radiation (rear lobe)?
I tried a metallic reflector which works well in terms of radiation, but considerably degrades the return loss and adds more complexity to the design.
0
votes
1answer
122 views
Gain in long wire antennas
DARA (you know, Hamvention) TNG is looking for projects. Thursday, I will be proposing building and characterizing a vertically-polarized 1 wavelength on a side reentrant rhombic.
Since in doing the ...
1
vote
1answer
141 views
SDR - discone antenna setup
Here's a picture of my SDR receiver setup...
This entire setup lives indoors as I'm not able to put anything up on the roof right now.
My understanding of a discone antenna is that the downward ...
1
vote
1answer
319 views
Designing VLF antenna
I was doing some research about the relation between wavelength and antenna size and shape. I was mostly interested in 15KHz rf range.
Based on my research I found the following:
A squarish shape ...
2
votes
2answers
104 views
Physics behind this decametric radio telescope
I am following this design for a simple decametric radio telescope.
I understand the principle that a radio wave hits the metal inducing an electric current that can be measured, but I do not ...
2
votes
3answers
119 views
Which antenna would you use?
I'm starting to study RF propagation at college, and I'm thinking about what antenna I should choose for this scenario:
The distance between the transmitter and receiver is just 700 meters, and the ...
3
votes
2answers
108 views
Can you create a radio beam with a Faraday cage?
Imagine we have an isotropic antenna at the origin emitting a steady sine wave at frequency $f$. Encompassing the antenna is a sphere of radius $r$ made of a fine copper mesh (with holes $\ll\frac\...
4
votes
3answers
1k views
Aluminum vs copper antenna element lengths
Does the particular metal used in antenna elements make any difference in element length or spacing, i.e. 1/2" aluminum tube vs 1/2" copper tube?
I know that length and diameter have an effect on ...
3
votes
3answers
109 views
Could 8' Marine whip antennas operate on much higher frequencies?
I have backgrounds on electrical communications, but know little about EM/RF.
I would like to install outdoor antennas for experiments (receive only; I do not hold licenses, although I do intend to ...
5
votes
2answers
118 views
Radials on a vertical, spread out evenly or not?
To have a groundmounted quarter wave vertical with a decent efficiency you need at least 16 radials.
So normally you would spread them out on the ground evenly around the base. This would give an ...
0
votes
3answers
184 views
Total cancellation in corporate feed network for patch antenna
I'm trying to build an array of patch antennas in order to receive a GPS signal. The idea is to build 4 patches and connect them with a corporate feed network. An example of corporate feed is this one....
2
votes
3answers
674 views
Feeding a dual-band UHF and VHF Yagi antenna
I just built a UHF Yagi antenna for my HT, and I was thinking about adding VHF elements. If I do, could I just connect the coax directly to both sets of elements without a diplexer?
1
vote
3answers
170 views
Would the antenna described work?
For reception of amateur radio satellites, turnstile antennas (consisting of two crossed dipoles fed out-of-phase) are often used.
I've recently had an idea - what if two half-wavelength dipoles are ...
0
votes
2answers
206 views
Do the radials of a quarter or 5/8 wavelength antennas connect to the braid of the coaxial cable?
I'm studying for my foundation license (in the UK) and I have these diagrams:
Do the radials in a quarter or 5/8 wavelength antennas connect to the braid/shield of the coaxial cable? If so, how does ...
1
vote
1answer
64 views
Resistance of antenna dipoles
A quick question: Is it a disaster if the two legs of a v-dipole antenna are different resistances? Thanks.
3
votes
2answers
537 views
Optimising a small magnetic loop with 1:1 SWR but little radiation
I'm trying to build a small magnetic loop for 5W on at least 40m - 20m following ideas of G4ILO's wonder loop. For this, I'm using coax with a ~2mm copper core and ~1mm spacing to the braid (see 1st ...
7
votes
6answers
455 views
Use a TV coax and balun for a poor-man's OCFD?
Can I use TV coax and a cheap TV balun to build a poor-man's OCFD? Marginal performance is acceptable if it saves money. If I could listen to 10% of transmitters within a 100 mile radius that would be ...
2
votes
5answers
163 views
What happens if an HF dipole is made longer?
Does a longer dipole (than half wavelength), for example twice as long, tuned to 50 Ω using an antenna tuner perform better than a half wavelength dipole for the same frequency?
3
votes
2answers
163 views
Loop Antenna - configuration?
Due to space limitations, I'm looking at loop antenna designs. I'm starting with receive only, but hope to eventually transmit.
I've seen magnetic loops (single turn with a coupled loop) and I'm ...
2
votes
1answer
214 views
What kind of antenna design is this?
I've found an old antenna that once came with an HP laptop with a TV (DVB-T?) card. I decided to see if I can use that antenna for something else, so I opened it up and found the following antenna ...
1
vote
1answer
315 views
How do I specify that wires are connected in 4NEC2?
I've been trying to get acquainted with the 4NEC2 antenna modeling program. Perhaps this is obvious, but it's not clear to me that wires with one end in the same place are connected. I'm attempting ...
3
votes
2answers
227 views
Tiger Tail + capacitive coupling… what's the interaction?
I've been working on a 2m setup for hiking. My goal is to have the best possible antenna that can be used while walking, and that won't get damaged if I walk under a low branch or some other forest ...
4
votes
3answers
427 views
Colocated three orthogonal wire loops for lightning detection network
I'm considering building multi-turn wire loop receive antennas for a blitzortung.org lightning detection receiver. It has three separate channels for H-field antennas, operating simultaneously.
...
2
votes
2answers
215 views
Satelite dish modified for Wi-Fi (Signal Elevation Question)
I am doing a project where I will be re-purposing an old TV satellite dish as a directional Wi-Fi antenna. The dish is circular in shape, not oval. The dish has an arm coming from the bottom that ...
2
votes
2answers
536 views
How much does the quality of coax cable matter?
I am using a bit of coax cable as an antenna (with the shielding off at the last 17.3 cm). However it is cheap Chinese cables and the shielding does not contain that many copper wires (the "web" isn't ...
4
votes
3answers
314 views
Can 2 uhf beam yagi antennas be used on a transmitter to get a diversity effect?
I'm having a problem getting a good signal up to a repeater site on UHF. I'm running 20W in a neighborhood with lots of trees, and the signal is fading in and out due to trees and the wind.
I can't ...
