Linked Questions

19
votes
5answers
9k views

How can I protect equipment against a lightning strike?

A lot of aerials (almost by design) would be rather good attractors of lightning. What steps do I need to take in the field to keep my gear safe against a lightning strike? I'm presuming the obvious ...
28
votes
5answers
33k views

Can I reduce RFI/noise at the antenna?

Recently, the power was out in my neighborhood for an extended period of time. I fired up my HF rig using battery power and was amazed at the lack of noise across the HF bands. When the power grid ...
9
votes
6answers
31k views

Is there a simple, DIY, antenna suitable for HF receive only?

So the antenna I'm thinking about doing might be* way too large for my property. Is there another simple, cheap, DIY antenna I could try on my receiver? I know I'm going to want to hook it up and ...
23
votes
3answers
35k views

Why are some 1:1 current baluns twice as complicated as others?

I would like to add a balun/choke to my dipole for the reasons outlined in Using a balun with a resonant dipole. In the spirit of continued kit and/or DIY building for my ham shack, I set out to ...
13
votes
3answers
7k views

How do I prevent radio signals from tripping a GFCI?

My wife woke up several nights by a metallic "thunk". It happened to be while I was talking on 10 meters and turned out to be the ground fault circuit interrupter (GFCI) on her hair dryer cord. ...
6
votes
8answers
9k 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 ...
13
votes
4answers
3k views

Handheld Dipoles

A problem with handheld devices is poor grounding. I read from someone else's question that dipoles don't need a ground. Why don't they make little handhelds with two antennas instead of one, or a ...
9
votes
5answers
4k views

Grounding a second-story shack with an outdoor antenna

My shack is on a second story, really far away from the house ground. To run a ground from my equipment to the outside/ground is a run of at least 60-75 feet. The antenna is at least 100 feet away as ...
6
votes
7answers
7k views

What is the attraction of vertical antennas for HF?

I understand that MW broadcast stations use vertical antennas because that polarization works much better for groundwave propagation. But in amateur radio, I would assume the focus for communications ...
14
votes
4answers
6k views

What does the addition of a shield to a small loop accomplish?

A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
5
votes
2answers
7k views

How to construct a loop antenna for receiving HF?

I have a unused hula-hoop in my garage, and I ran some stranded speaker wire around it once, and attached one side of the wire to the coax shielding, and the other to the coax core wire. Is this the ...
12
votes
2answers
4k views

Is there an optimum Antenna Feedline Length for mobile installations?

I bought a ham radio antenna mounting kit for my car that includes ~16' of coax. One end has a trunk lip NMO antenna mount, the other end has a re-solderable PL-259. I asked the sales person if it is ...
9
votes
2answers
8k views

Grounding VHF base station antenna

I'd like to install an outdoor dual band VHF/UHF base station antenna, a simple pole antenna like the Comet GP-1. I live in an area where lightning is rare, but not unheard of. Should I drive ground ...
7
votes
2answers
1k views

Dipole Antenna Current Distribution at any Time Instant

Above is a connection of half-wave dipole antenna. The book states that the current profile is same at any given time instant on both the radiators, each of quarter wavelength length. Now my ...
4
votes
5answers
5k 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 ...
4
votes
2answers
6k views

Coaxial Folded Dipole Antenna Matching Impedance

In http://www.nsw.wicen.org.au/technical/projects/coaxial-folded-dipole-antenna, the guy is using a 50 ohm coax cable to build a folded dipole antenna and claims that this will enable use at 50 ohm (I ...
5
votes
5answers
552 views

Signal path to maximize RFI rejection in an urban environment

Urban ham here (Cambridge, MA - FN42ki - KC1JZE) looking for tips to make this hobby possible in the city. I rarely can hear both sides of HF phone transmissions, and have yet to make contacts despite ...
1
vote
3answers
1k views

How to attach a magnetic loop antenna to the 50Ω coax of an RTL SDR?

I'm planning to make a magnetic loop antenna mainly for receiving LW, MW, and SW radio broadcasting bands, as well as perhaps the 2.2km band and 630m band. (Not all of them with the same antenna, I'mm ...
7
votes
4answers
3k 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 ...
1
vote
4answers
2k views

Is the ground on the back of the Icom IC-7300 an electrical or RF ground?

On the back of the Icom IC-7300 there's a ground connector: The manual goes on to say this: Is this an electrical or RF ground?
2
votes
3answers
3k views

Choke at antenna and feedpoint?

I'm planning on putting up a G5RV. From the ladder line I connect 5m coax to the shack; would it be worth doing a common mode current choke at both the antenna feedpoint and the coax feedpoint? (I ...
5
votes
3answers
981 views

Is this the Correct Ferrite Core to Reduce RFI as a Common Mode Choke?

I have a Flex 3000 connected via RG-11 coax to a inverted V fan dipole tuned for 40m and 20m on my roof. I have an "ugly" balun up on the mast by the antenna. I further have the feed-line going into a ...
5
votes
2answers
714 views

RF Antenna - V pole - Should one leg go to ground and the other to signal?

I'm attempting to follow this white paper in order to build an antenna. This is my first antenna and as such I have a rather simple question. DIY 137 MHz APT Weather satellite antenna by Adam-9A4QV ...
6
votes
2answers
2k views

Understanding coax radiation and “current on the shield”

I'm having trouble understanding what seems to be the fundamental principle behind baluns (and probably other related topics). Perhaps some of my confusion comes from an audio background, where one ...
6
votes
3answers
2k views

Impedance Matching Different Feedlines

(I promise there will be a question in this wall of text. I'm just giving context.) I've been wanting to try my hand at building my own antenna system for the last few weeks and in doing research, a ...
4
votes
2answers
3k views

Does effective grounding of mobile (vehicle) antenna mounts address common-mode currents?

While researching how best to install my mobile amateur radio in my car, I didn't understand if there was optimum Antenna Feedline Length for mobile installations? Understanding that this is caused ...
2
votes
1answer
1k views

Do I need a Balun for a single band QRP antenna?

I have a little MFJ QRP CW 20m rig that I plan to turn into a portable kit for SOTA peaks. I have everything figured out except for the antenna. I am wanting to make a dipole. However, I was wondering,...
4
votes
1answer
1k views

Antenna, input and ground bonding

I'm new to this and am in need of guidance. I am mounting a multi-band antenna on a 50 foot tall 1 1/4" galvanized mast. I plan to drive a ground rod at the base of the antenna and bond the mast to ...
2
votes
3answers
2k views

What does it mean to have “RF in your signal”?

I've been told that I have "RF in my signal". What does this mean? What are some potential causes of having RF in the signal?
5
votes
2answers
388 views

Will measuring SWR through a feed line mislead me?

I know that except in the perfectly matched case, transmission lines transform impedances along their length; if I measure the impedance at the other end of my feed line, or even with a short jumper ...

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