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 How to mount my 1/2 wave silver rod

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Kittiwake
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Kittiwake


Call Sign : 163-CT-234 / MW7WYN
Posts : 29
Times Thanked : 4
Join date : 2020-03-01
QTH or Location : Swansea
Equipment Used : CB>>Homebase: SS6900n with 1/2w silver rod, Mobile: CRT Millenium (V3) with mini springer......HAM >> Anytone D878UV
Age : 57

How to mount my 1/2 wave silver rod Empty
PostSubject: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitimeTue Apr 28, 2020 2:09 pm

Hi all,  
I will soon be getting a new Aerial, (1/2 wave silver rod)
While reading through other members posts they mostly go on about mounting onto a metal post.
My questions are,
1    does the post act as a ground plane?
2    can I mount the silver rod to the top of a 4x4inch 20ft wooden post?
2a  If I do, will I need to run a grounding wire from the mounting bracket back to a copper
      grounding rod?

Any advice/suggestions will be greatly received

Kittiwake
Arwyn
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BigTone
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How to mount my 1/2 wave silver rod Empty
PostSubject: Re: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitimeTue Apr 28, 2020 2:55 pm

Arwyn
If you mount it on a wooden pole, it would be a good idea to run a (thick if poss) wire to the ground for dumping static. A metal pole will would dump the static buildup.
The 1/2 wave doesn't need ground planes as it is a dipole that is end fed rather than centre fed.
It would be a good idea to wind a choke as close to the aerial as possible.
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Northern Crusader
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Call Sign : M0GVZ / 26CT1760
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How to mount my 1/2 wave silver rod Empty
PostSubject: Re: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitimeTue Apr 28, 2020 3:28 pm

BigTone wrote:

The 1/2 wave doesn't need ground planes as it is a dipole that is end fed rather than centre fed.

Completely wrong. ALL END FED ANTENNAS NEED A RF GROUND. It isn't an "end fed dipole" at all, no such thing exists. Kirchoffs Law applies and you can't get around it unless you've found a way of changing the laws of physics.  Kirchoffs Law says the current leaving one point must be matched by current entering the same point from some other path or paths. In other words, at any junction, we cannot force current out into something without the same net current coming from something else.

This means we cannot force power into a single terminal load. There has to be a return path of some type, even if it is not obvious. The path in a high frequency AC system (like an antenna) does not need to be a direct connection. The path can be through displacement currents (currents through electric fields), but there MUST always be a return path to the source. In the Zepp antenna system, or any end fed half wave, this displacement current must get back to the feed line somehow.  If it didn't, it would have no current at the ends.

In a normal "push-pull" center fed  fed dipole, displacement currents largely (but not totally) flow from one side to the other. This establishes the electric field, and allows current to flow outwards into the wires hanging "open" in space. With an end-fed, current flowing from the stub or feeder out into the end of the radiator must be returned to the opposing conductor of the feed line. This returned current (called displacement current) always equals the common mode current flowing into the antenna end. Without a suitable counterpoise, common mode or radiating currents must flow onto the feed cable or supporting mast. This means, lacking a proper counterpoise and common mode isolation, an accidental (and generally unwanted) feed line or mast common-mode current must exist.


Sure it'll work if you don't put one in but only because it's using the pole but more likely your coax to make up for one.
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BigTone
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Call Sign : G8YMW or 26CT4498
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PostSubject: Re: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitimeTue Apr 28, 2020 11:56 pm

I cannot word it right but you are wrong about the end feed half wave.
Lookk at the RF currents and voltages.
A centre fed dipole is high current - low voltage at the feedpoint (~72 ohms, good match for coax)
An end fed 1/2 wave is high voltage - low current at the feedpoint so you cannot feed directly with coax so you have to do something different. You shunt feed it, that is a short across the coax (using a coil) and the element is tapped off that coil. No radials needed.
A 5/8 wave, on the other hand is a 3/4 wave electrically and needs radials or something
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Kittiwake
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Call Sign : 163-CT-234 / MW7WYN
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Join date : 2020-03-01
QTH or Location : Swansea
Equipment Used : CB>>Homebase: SS6900n with 1/2w silver rod, Mobile: CRT Millenium (V3) with mini springer......HAM >> Anytone D878UV
Age : 57

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PostSubject: Re: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitimeWed Apr 29, 2020 12:38 pm

Thanks BigTone and Northern Crusader for your replies.


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Kittiwake
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New Member
Kittiwake


Call Sign : 163-CT-234 / MW7WYN
Posts : 29
Times Thanked : 4
Join date : 2020-03-01
QTH or Location : Swansea
Equipment Used : CB>>Homebase: SS6900n with 1/2w silver rod, Mobile: CRT Millenium (V3) with mini springer......HAM >> Anytone D878UV
Age : 57

How to mount my 1/2 wave silver rod Empty
PostSubject: Re: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitimeWed Apr 29, 2020 12:39 pm

My Aerial has arrived and I'm trying to put it together, there was no Information/instruction leaflet included, the extending legs have no marks to indicate the length for clamping.
Is there a guide length I should put each leg into the other as a starting point
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PostSubject: Re: How to mount my 1/2 wave silver rod   How to mount my 1/2 wave silver rod Icon_minitime

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