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.

Filter by
Sorted by
Tagged with
2
votes
2answers
291 views

dual band j-pole creates connectivity problems when connected all the way

I recently made a "deseret j-pole" dual band antenna for basic 2m and 70cm transmitting and receiving use. I have it on a large metal tube behind my house, connected through a 50 ohm pl-259 cable, and ...
6
votes
1answer
409 views

What kind of antenna is this?

This was found among some old ham stuff and is believed to have been used on 2 meters. The vertical elements are 17 1/2" long and the connector on the bottom is a standard SO-239. Antenna (left) and ...
1
vote
2answers
1k views

How to best connect an FM transmitting GPIO pin to an antenna?

I'm trying to use a RaspberryPi3 as a FM transmitter, using pifm and/or PiFmRds to send audio in 88-108 MHz band. The RPi can then use the GPIO-4 pin to transmit between ...
0
votes
1answer
1k views

My Baofeng radio won't recieve but transmit does not work when I hold the MONI button [closed]

My radio won't receive. Help? It literally went dead and I still have the rubber duck antenna
3
votes
1answer
403 views

Using an HF antenna for VHF scanning

Are there any disadvantages (or advantages) to using a long-wire HF antenna for wide-band VHF reception? Or would feedline losses make that useless compared to a ground level ducky or short whip? (...
1
vote
3answers
341 views

High SWR on a Jeep with Spare Tire Mount

I just installed a spare-tire mount and Browning BR-180 dual band antenna on my Jeep JK. Initial SWR testing show nothing higher than 1.4:1 across both bands so I didn't try to tweak it. Then I put ...
4
votes
1answer
402 views

DAB antenna in roof space

We are setting out our roof-space as an attic, and after decorating, there will be a triangular void under the house ridge, which will be about 36" wide, and 18" high. I can easily fit a standard ...
1
vote
1answer
371 views

How to assemble an antenna (impedance matching methods)

I got the following plans off Martin E. Meserve's website. How do I go about assembling the antenna once I have the elements and boom? What is the impedance of the driven element? Do I need baluns ...
4
votes
1answer
695 views

What is the difference between “Cross Polarized” vs “Circularly Polarized” Antennas?

What is the difference between cross-polarized yagi antennas and circularly polarized antennas?
0
votes
1answer
52 views

Transmission Line Model of Co-ax Lines

I have got 2 questions on transmission line. In coax line, the centre wire is Copper, and the outer line is Aluminium, as far as I can see in the coax that I have. I have got couple of questions on ...
3
votes
3answers
496 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 ...
2
votes
3answers
355 views

Maximum Thickness for NMO Mounting Surface?

How thick can the metal be for a common NMO antenna mount? I know they're meant for sheet metal but can they go as thick as 1/4"? Edited to add: By "common", I mean NOT the ones designed for extra ...
1
vote
1answer
200 views

Antenna Ground System

I have a designed an arrayed dipole antenna for transmitting in 200MHz frequency. Where I am confused is, what should be my ground system for both antennas (Transmitting, and Receiving). Say I am ...
0
votes
1answer
310 views

What is the directivity of thin dipole antenna of length 1.25λ?

I want to know about the directivity of thin dipole antenna of length 1.25λ for my assignment.Is there any formula related to its length?
2
votes
2answers
1k 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 ...
2
votes
1answer
260 views

Rules of thumb for large (“somewhat” full wavelength) loop antennas?

I would like to put up a relatively large loop antenna to cover all the HF bands. I have sloping terrain and geographically in a slight "bowl" with hills and/or ridges in many directions. If I stick ...
1
vote
1answer
87 views

Ramsey's DDF1 with a SMA connector

Need some help with my Ramsey DDF1. It comes with telescopic antennas and my son has accidentally stepped on and broken one. I'm taking the opportunity to replace them with a SMA connector and ...
7
votes
2answers
986 views

Moon->Earth 433MHz link achievable digital bandwidth

Let's assume we have the following situation: Transmitter on moon orbit (distance from earth ~400'000km), around 433Mhz. Transmitter power 1W, antenna gain 10dB, circular polarization. Steered to ...
2
votes
2answers
2k views

How far does a watt equal in range in the FM band?

How many watts would be needed to cover a 10 mile radius with good sound for music on the 88-108 MHz FM broadcast band? I am an amateur and for fun only.
1
vote
2answers
130 views

Serial matching stub combined with RF choke

If I use RG6 coaxial cable in odd multiples of 1/4 wavelength as a serial matching stub, can I also use it, without modifying the length, as a coiled RF choke balun at the antenna feed point?
3
votes
1answer
253 views

Mathematica notebook for NEC2 (NEC, Numerical Electromagnics Code)

Are there any open source Mathematica notebooks that interface with NEC2? I am primarily interested in plotting the NEC2 results from Mathematica.
3
votes
2answers
5k views

How the Coaxial Collinear Antenna Works?

A length of coaxial cable radiates negligible amount of RF. Same length, if cut into pieces of length (λ/2 * VF), and these pieces joined again cross-connected (i.e. core of a piece to shield of ...
5
votes
8answers
6k 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 ...
1
vote
2answers
251 views

Tuning an antenna with cold weather

I have a 20m long dipole that starts at 2m above the ground and ends at perhaps 20m above the ground. It was -10 °C here tonight (that's +14 °F), currently around zero (32 °F) and my antenna is out of ...
1
vote
0answers
91 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?
2
votes
2answers
144 views

Interpretation of NASA design

I'm very interested in replicating a design published by NASA here : https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19670027843.pdf Specifically the arrangement on Page 11. I have a similar ...
2
votes
2answers
2k views

Does antenna frequency matter when trying to pick up radio waves?

I'm buying the following: https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Defined/dp/B0129EBDS2/ref=sr_1_3?ie=UTF8&qid=1480215974&sr=8-3&keywords=RTL-SDR to analyze radio waves as ...
1
vote
1answer
139 views

Utility pit MW/LW omnidirectional antenna

I am looking at antennas for a rather unusual application: mounted under a utility pit lid (manhole cover). The goal is to receive commercial MW/LW stations. The antenna has to be attached to the ...
3
votes
1answer
156 views

Polarisation loss Dipole antennas

For a school assignment I need to calculate a link budget between two half wave dipole antennas, but I am stuck at calculating the polarisation losses in the antennas. the antennas are ideal and ...
11
votes
2answers
359 views

What kind of antenna is that one?

Yesterday I saw the following antenna: I am very puzzled, at first glance it seems a simple dish but: The mesh is really wide (low frequency?). It is pointing to Zenith. I think that most dish ...
2
votes
1answer
204 views

Influence of bending and asymetric ground wire on monopole antenna

I'm currently building a rc radio system using the 433mhz RFM69W transceiver, so far everything works fine, but i am not sure about the way i laid out my antenna and how the layout cripples the ...
2
votes
1answer
104 views

Portable radio antenna measurement

Just purchased a HP 8711A and have "upgraded" the bootrom to enable vector measurements. I am now trying to learn more about how to make better measurements and understand what's going on. One of the ...
3
votes
2answers
353 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?
1
vote
4answers
627 views

Is it safe to live close to cellular antenna?

I saw some apartment in my county in a very good location (quite close to the beach), however, the rent is very cheap. The apartment is the highest on that building, on top of this building there is a ...
8
votes
2answers
767 views

cubesat turnstile antenna material selection

My cubesat team is working on our design for rolled whip antennas to deploy in a UHF turnstile configuration based on this design: What I would like advice on is the material for the antennas ...
3
votes
3answers
559 views

Why does an “electrically small” antenna have narrow bandwidth?

Reading this interesting piece on magnetic loop antennas, the author explains that a magnetic loop has great efficiency even at small size, but the the price you pay is very narrow bandwidth. Why is ...
0
votes
2answers
2k views

DIY 433MHz antennas from copper wire

I need to build two minimalistic antennas for RX/TX at ~433MHz. I have insulated solid core copper wire, but I need to make it perfectly straight. I was thinking of using the type of sticks you set ...
5
votes
3answers
385 views

Mounting my antenna

I just bought a CB and mounted it in my truck. I ran my antenna to the back and was going to stick it to my tool box but it turns out to be aluminum, so I'm thinking of bolting a metal plate to the ...
5
votes
3answers
4k views

Distance between antenna and radio

I live in a small cottage with an unlevelled terrain. My house was built in the lower part of it (left-side), and in the other half of it there is a hill. On top of the hill there's a fairly good ...
1
vote
3answers
213 views

How to calculate/estimate the effect of having conductive material nearby an antenna

I have a system with a 1/4 wave whip antenna and above the antenna there is a mess of aluminium they're not connected but are nearby. I would like to figure out what effect this would have on the ...
7
votes
3answers
2k views

Antenna for a cramped attic

Brand new Ham. I bought a cheapo UV5 right before I got my call sign. I want to set up a decent 2m/70cm station for starters and I realize that a better radio is important but wanted to knock out the ...
1
vote
1answer
390 views

Best way to make a selfmade Long-Range WiFi Link

What needs to be considered? Which type of antenna(only self-made or reused parts, for example satellite dish) is the best for a long range, high throughput WiFi? How to calculate Antenna size and ...
0
votes
3answers
2k views

Will two ends of dipole antenna pointing to the same direction cancel out the signal

I am living in a small compartment, considering setting up an antenna indoors. As my room is so small (3m^2), thinking of putting a dipole antenna with soft wire indoors. If two ends of dipole ...
0
votes
1answer
87 views

Directional antenna overlapping main lobes

In a 2-Rx by 2-Tx directional antenna system, say both transmitters are transmitting concurrently as in Fig. The main lobes from the two transmitters overlap. How does this affect the resultant signal ...
2
votes
3answers
4k views

Calculating bandwidth of antenna?

Is there a way to calculate bandwidth of an classical dipole antenna having this information: center frequency wire velocity wire diameter I would disregard antenna height, to simplify. I am not ...
3
votes
3answers
490 views

Which is better in my situation: Balanced dipole, or as much wire as possible in the air?

I'm finally getting to the point of hopefully putting up a HF antenna. The idea is to start with a simple, straight wire dipole using trees as support points. (No traps or coils.) However, with the ...
3
votes
1answer
249 views

How to calculate effective isotropic radiated power apply to lossy antennas

If a band allows one watt EIRP and I have an antenna that is 1% effective could I legally run 100 watts into the antenna because only one watt is radiated? If that same antenna also has a gain would ...
1
vote
2answers
218 views

Strange Noise Floor observed in UHF Band

I have a tracking station for UHF band satellites which comprises of a cross yagi of 12 dBi and a wideband LNA of 40 dB Power Gain and 1.3 dB Noise Figure. I observe a Noise floor of about 300 kHz ...
3
votes
2answers
340 views

Combining yagi and J pole for airband

I use a J Pole for air band (122 MHz). I get superb aircraft reception but a very weak signal from my local airport 20 miles away. Is there a way to set up a yagi, or other gainy directional antenna, ...
0
votes
1answer
137 views

Feed line direction for Quad antenna

I am currently getting my EE degree, and I'm trying to build my first antenna for a weather balloon. I understand with a dipole, you want the feed line perpendicular to the antenna for at least l/4, ...