[TowerTalk] Rai Beam
wa4dou@juno.com
wa4dou@juno.com
Tue, 11 Apr 2000 22:36:47 -0400
Hi Bruce,
Isn't this fun? Ha! I have to point out the the change in gain of the
antenna has no effect whatsoever on the takeoff angle. The angle of
radiation is solely established by the height of the antenna above
ground.
My reference to the use of the step attenuator is solely for the
purpose of learning what change a db, 2 db, 3 db, 4 db, means. Please
read my correspondence carefully. Do not read into it what i have not
said. I have not suggested that you should use it to guage operating
conditions in the midst of many signals comming from everywhere. That
would be meaningless. I believe a carefull, dispassionate reader knows
what i said and meant.
73 Roy WA4DOU
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On Tue, 11 Apr 2000 13:15:41 +0000 wd4ngb <wd4ngb@qsl.net> writes:
> Roy and others,
> And I would have to disagree with you. Using a step attenuator to
> change
> ALL signals 3 db is a lot different than changing one in the
> direction you
> are
> wanting to work, and reducing qrm from other areas. A 3db change in
> gain
> on a antenna will also change your take off angle, which has a
> dramatic
> effect
> on DX contacts that can not be checked with a attenuator. 73/DX,
> Bruce
>
>
> wa4dou@juno.com wrote:
>
> > Mauri,
> > Respectfully, i'll have to disagree with you. I've seen few
> cases where
> > 3 db would have done anything for me. I work mostly cw, and
> occasionally
> > work signals in the noise. Furthermore, i'm a qrp'er, running
> mostly 5
> > watts and under. 3 db is not much gain. I challenge you and all
> other
> > list subscribers to obtain a step type attenuator, install it in
> line,
> > and switch it in and out in a variety of situations. Except in the
> noise,
> > 3 db will not make or break your communications. And if i do miss
> the dx
> > today, it will be back tomorrow. 5 watts is 13 db down from 100
> watts and
> > 23 db down from 1000 watts. Propagation is a great leveler of
> signals. 73
> > Roy WA4DOU
> > P.S. You are right, gain is a direct function of boom length.
> Thats an
> > entirely different subject.
> >
>
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> >
>
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> >
> -----------------------------------------------------------------------
> >
> > On Tue, 11 Apr 2000 10:49:12 +0200 "i4jmy@iol.it"<i4jmy@iol.it>
> writes:
> > > It depends by the S/N situation, but in most cases a 3dB gain is
> a
> > > lot,
> > > "to hear or not to hear".
> > > Stated it, the gain in yagis is a direct function of boom
> lenght.
> > >
> > > 73,
> > > Mauri I4JMY
> > >
> > >
> > > > ---------- Initial message -----------
> > > >
> > > > From : owner-towertalk@contesting.com
> > > > To : towertalk@contesting.com
> > > > Cc :
> > > > Date : Mon, 10 Apr 2000 14:05:30 -0400
> > > > Subject : Re: [TowerTalk] Rai Beam
> > > >
> > > >
> > > > Hi Joe,
> > > > Reviewing a few known facts, i remember that the ZL Special,
> a
> > > dual
> > > > driven
> > > > phased array, has a gain of about 3 dbd. The 2 element yagi
> > > produces a
> > > > gain
> > > > of 4.5-5 dbd, the 2 element quad produces a gain of 5-5.5 dbd,
> the
> > > 3
> > > > element
> > > > yagi produces a gain of about 6 dbd, the 4 element yagi- about
> 7
> > > dbd,
> > > the
> > > > 5
> > > > element yagi- about 8 dbd, so on. Beyond about that limit, the
> > > gain
> > > > starts to fall
> > > > below 1 db per element.
> > > > I don't believe for a second, that the 2 element Raibeam
> > > produces a
> > > > gain of 8
> > > > dbi, which translates into 5.9 dbd., but for the sake of the
> > > arguement,
> > > > lets assume
> > > > that it does, for a moment. (Does anyone know how the Raibeam
> > > differs
> > > > from
> > > > the ZL Special?).
> > > > First and foremost, the advantage that one enjoys with most
> > > antennas
> > > > with
> > > > directional characteristics, it that they are raised to a
> height
> > > that
> > > > places their
> > > > lower lobe in the range of angles of radiation that are
> > > appropriate
> > > to a
> > > > particular
> > > > path. Even a dipole would perform well under such
> circumstances.
> > > Its
> > > > therefore,
> > > > not surprising that "trapped" tribanders with typical gain
> figures
> > > of
> > > > 1-1/2 to 3 dbd
> > > > would also perform well. Likewise, the ZL Special, 2 element
> > > yagis,etc.
> > > > The
> > > > differences between all these antennas are only a few db.
> Without
> > > a
> > > > reference
> > > > antenna for comparison, most of us would be hard pressed to
> even
> > > know
> > > > that there
> > > > was a difference, except intellectually. A difference of 1 db
> is
> > > so
> > > > insignifiicant that
> > > > even under closely and carefully controlled conditions, most
> of us
> > >
> > > could
> > > > only just
> > > > barely discern that level of difference between two signals. A
> > > difference
> > > > of 3 db isn't
> > > > remarkable( to quote Bill Orr), 5 db is a worthwhile
> difference
> > > (again, to
> > > > quote Orr),
> > > > and a difference of 10 db, is a new level of performance, but
> > > still
> > > only
> > > > the difference
> > > > between an s-9 signal and one 10 db above s-9, IF, the "S"
> meter
> > > is
> > > > accurately
> > > > calibrated.
> > > > I will continue this in PART 2. 73 for now, Roy Lincoln
> WA4DOU
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