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Low band Vertical og Jordplan

: tirs mar 30, 2021 17:57
af oz7c
Hej

På lowband har der været artitler omkring Jordplan
Til Vertivcal TX Ant (inv-L mm)

Der er 3 udgaver

1 Radialer på jorden antal/længde
2 Elavated Radials 2-4 stk
3. Counterpoise

Alle udfra hvad man har plads til for at få mest udstrålet antal Watts

Her er et copy af K2AV der har designet Counterpoise systemet

It sure seems like a lot of confusion arises when folks attempt concise
electrical and mathematical thoughts and calculations using words with very
broad and fuzzy definitions. Words like radial, vertical, topload, etc.
can mean different things and can create remarkably confusing sentences and
descriptions.

Like “vertical with one elevated radial”. If one is thinking that radials
are a specific kind of wire group used as a counterpoise that effectively
minimizes radiation, then “with one radial” can’t be called a radial. It
simply is one end of a bent dipole, with one wire very close to and
parallel to the ground. Less lossy than some constructions, e.g. the
horizontal wire actually laying on the ground or buried, but decidedly
lossy. But there will be disagreement about a bent, ground-adjacent dipole,
quite more than one way of talking about that.

Being accused of not having a radial will undoubtedly be defended with "I
worked VK9ABCD at noon long path with a vertical over one radial." But
that comeback does not pay any attention to whether one can include "one
radial" in a precise definition framework for discussion about how radials
work and why the commercial gold standard radials work so well. And of
course the worst of antennas can sometimes make QSOs in the best of
conditions, while the best of antennas can often barely make QSOs in the
worst of conditions. How can one possibly have an academic grade discussion
with all that flak flying around under the same list-serve thread title?

Since it’s not possible to referee a precise dictionary of such terms that
everyone will agree on, the answer to questions can’t be precisely
formulated with those terms IF what we’re looking for is precise answers or
at least answers good enough to risk precious hours, sore backs and
monetary expenditures.

In the end the answer to what wires and aluminum tubes do is what the
antenna modeling says they do, assuming that attempting the actual antenna
doesn’t expose a gotcha that requires additional work to produce in the
model what the wires and tubes actually individually do. The antenna model
is the only device we have that can break down the problem into small
pieces, calculate all the micro-interactions, and then add them up into
patterns and gain figures.

But even the high-priced pro antenna modelers get tricky to do right with
conductors very close to or in the ground, especially an issue on 160m.
Losses are the two ton elephant in the room on 160. Conversations with
fuzzy terms and concepts don't have a chance at accurately telling you
about RF losses, other than to warn they need to be dealt with.

We estimate efficiency by constructing the idea in a model, comparing
average and worst case ground results, and then doing a near field run set
to the ground surface. The former tells you how badly ground could affect
the performance and the latter shows if the design has created hotspot RF
field zones that can excessively induce ground losses, possibly pointing to
design improvements without the hotspots.

Verbal discussion is good for airing general ideas and concepts, providing
mental constructs for at least basically understanding involved
principles, if you can get consensus on definitions of terms. But as soon
as you want to know dB's, whether A is better than B, or not, you have to
do the work to put the idea up in models, avoiding all the gotchas, so all
the interactions between conductors, between conductors and ground, can be
calculated, added up and presented as loss figures and radiation patterns.

As to your mention of a typical VHF ground plane with counterpoise members
in a plane perpendicular to the radiating member, far field radiation from
those four will be minimized. When those four are "drooped", the four now
have a vertical component to their fields which modifies the pattern of the
main radiating member.

Frankly I think that the VHF "coaxial dipole" has long since replaced that
design. Consider the Celwave Stationmaster, etc, since even barely high
angle VHF radiation is lost altogether. One of their improvements in those
fiberglass encapsulated collinear antennas is to produce patterns that max
out three or even six degrees below perpendicular to the vertical to aim
max power "down" to the horizon or nearer service area from their high
mounting points. I don't see radials on those things. Still on some simple
low VHF antennas.

Using "down-angled" elevated radials in a 160 antenna has mild advantages
seen on a model. But one's physical construction has to have something
handling a loss avoidance need to keep RF off the tower beneath the
feedpoint. That seems to discourage that idea from becoming
popular, because without defeating RF on the tower beneath, that added loss
more than cancels the mild advantage seen in simple models without the
tower-to-ground treatment.

There actually is a way to accomplish tower loading, without tower base
radials using one or two FCP's, a vertical wire parallel to the tower, and
a horizontal from top of the vertical wire, or a top FCP, a REQUIRED
isolation transformer, and a positioned short between the vertical wire and
the tower which MUST be the only copper connection between the L/FCP and
the rest of the world. The version with an L is described on k2av.com,
click on "65+ Tower L Bend". The version with a top FCP is experimental
and as yet without the mountain of NEC4 runs that determined the
positioning of the short between vertical and tower.

K2AV


73 Boye

Re: Low band Vertical og Jordplan

: ons mar 31, 2021 18:36
af oz1iky
Elevated Radials ...

Jeg fik en gang en artikel af en venlig radio amatør (jo de findes skam!) fra Force 12 om det med eleverede radialer.
Det var en erfarings-opsamling fra en Contest Gruppe, som havde QTH på 6Y Jamaica.

Deres QTH var godt nok tæt på vandet, men desværre langt oppe af en klippe-kant.
Så de kunne hverken udlægge en myriade af radialer, eller rigtig gøre brug af
nærheden til saltvandet - som kva et fald på over 100 meter ned, ikke var der alligevel.

Så de ekselerede en del med eleverede radialer.
Første gang jeg så det in action var på Bonaire (PJ4C).
Norbert DJ7JC havde en 4-SQ med. Men med en eller to radialer per GP...
Det virkede meget godt og overbevisende.

Det jeg kan huske fra artiklen er at man fra fødepunktet i bunden går 45 grader op
til den højde som der skal være på det pågældende bånd - og så ellers der ud af.
Helst med 2 radialer. Og de skal afstemmes som en NVIS dipol.

Vi prøvede det på cuba i 2016 - helt nede ved stranden med en GP til 160 meter.
Virkede IMPONERENDE godt. Jeg kørte flere Europæiske stationer med kun 10 watt på 160.

Force 12 folkene skrev at man på 160 meter skal hæve radialerne med 4 meter,
på 80 meter med 2 meter og på 40 meter med 1 meter. Og de 45 grader op, ind til du rammer højden.


God fornøjelse med at eksperimenterer med det. Det kan faktisk godt betale sig at lege med.


VY 73 til de fleste, og en god Påske til næsten alle.


Kenneth OZ1IKY

Re: Low band Vertical og Jordplan

: ons mar 31, 2021 22:31
af oz7xf

Re: Low band Vertical og Jordplan

: søn apr 04, 2021 3:34
af oz7c
Hej
Nu er der også andre grundet til at de skal op i mere end 2 M.
De er ligeså farlige som selve antennen, giver brandskader ved berøring !
Der løber HF strøm i dem som modvægt til ant.

De er mere effektive end et dårlig jordplan

Her er et andet emne nemlig træers indflydelse på vertical ant

That is a very important question and the answer may surprise a lot of folks
on Topband. Kay KE4PT worked several years on Motorola simulation RF in
hollow bodies for pagers and handheld close to the human body
Kai Siwiak KE4PT, QEX Editor. Kay prepared this presentation for our local
DX club.

https://qsl.net/k4fk/presentations/2018 ... -SFDXA.pdf

A Dipole 0.2 Wavelengths from a Tree looks like a 2-element Yagi on 30 MHz.
on 160m the F/B only 1 db.

kommer fra N4IS

Jeg har selv set eksemplet med en 80 vertival tæt op af et grandtræ
efter en del år var det slut med grandtræet der gik ud og senere brækket i en storm !


73 Boye