[CQ-Contest] Re: 2 dB more?

[Marijan Miletic, S56A]

Gain always remains the product of directivity and efficiency.

Antenna system design with optimal radiation angles is an entirely different
matter.

KISS de Mario, S56A, N1YU

----- Original Message -----
From: "Maurizio Panicara" <i4jmy at iol.it>
To: "Marijan Miletic, S56A" <artinian at siol.net>; <cq-contest at contesting.com>
Cc: <Matjaz.Vidmar at fe.uni-lj.si>; "Tom Rauch" <w8ji at akorn.net>
Sent: Monday, December 31, 2001 12:44 PM
Subject: Re: [CQ-Contest] Re: 2 dB more?


>
> Hi Mario,
>
> I agree, but that relation is incomplete of real factors, at lest for HF.
> The best inherent antenna efficiency,in other words how much the energy is
> transformed to EM field compared with the supplied energy, may still not
> result in a proper system efficiency.
> Two different antennas with same gain and efficiency can really perform
> different because of a different design or because of the installation or
> environment.
> As well as a very efficient antenna is always welcome, such an object may
> still not radiate best to desired directions or elevations. Eventually it
> may efficiently radiate where it's needed but also where it's not desired
it
> does.
> A typical case of good efficiency and poor results is an horizontal dipole
> or a yagi that because of a peculiar height from ground fires upward or
> anyway show losses at certain elevations if compared with another
radiator,
> even much less efficient, but placed at a proper or strategical heights.
> Under a system perspective, in HF a good designed stacked array whose
actual
> net gain could be abt 2-2.5 db, will gain much more for a stated period of
> time than a single new antenna having the same 2-2.5 dB gain over the
> original.
> Similarly, a vertical antenna over a bad ground, and for ground I mean the
> envirinment not the ground plane or the counterpoise, doesn't radiate a
> consistent energy at very low angles although its inherent efficiency
could
> be big.
> Such inherently efficient vertical will result terribly *inefficient* in
> bands like 10m where unity degrees elevations are often fundamental.
> All considered a 2 dB gain is not a little improvement, but may not help
at
> all as desired.
>
> 73,
> Mauri I4JMY
>
>
>
>
>
> ----- Original Message -----
> From: "Marijan Miletic, S56A" <artinian at siol.net>
> To: <cq-contest at contesting.com>
> Cc: <Matjaz.Vidmar at fe.uni-lj.si>
> Sent: Monday, December 31, 2001 2:13 AM
> Subject: Re: [CQ-Contest] Re: 2 dB more?
>
>
> >
> > Dr. Matjaz Vidmar, S53MV, professor of electromagnetics at Ljubljana
> > University
> > points out that hams are not aware of a very simple relation:
> >
> > Antenna gain is a  product of directivity and efficiency.
> >
> > Unless one doesn't use resistive loads for broadbanding antenna, poor
> traps
> > or grounding system for verticals, HF efficiency is very close to 100%.
> >
> > Special receiving antennas are another story.
> >
> > 73 de Mario, S56A, N1YU
> >
> > ----- Original Message -----
> > From: "Tom Rauch" <w8ji at akorn.net>
> > To: <cq-contest at contesting.com>; "Salina Physician Anesthesia"
> <spa at tri.net>
> > Sent: Monday, December 31, 2001 12:41 AM
> > Subject: Re: [CQ-Contest] Re: 2 dB more?
> >
> >
> > >
> > > > I have been using a KT-36XA in the last few contests.  Joke is that
> > > > I've basically only worked 10M as I am really a DXer first and don't
> > > > like getting a run going as I can't handle the mess.  However, it is
> > > > nice to call into a pile and get in on the first call.  And then
there
> > > > are the weak stations that plead for a contact and they are in the
QRN
> > > > with syllables only.  A few dB more and?  Or would I just find
another
> > > > layer?
> > >
> > > The common myth is if you have more antenna "gain" the gain also
> > > improves reception. That isn't true, unless you have a relatively
> > > "insensitive" receiver.
> > >
> > > The **directivity** of the antenna system determines the receiving
> > > ability, not the "gain". Directivity does NOT include losses, it is
> > > only a measure of the peak response in the direction of signals
> > > compared to noise or unwanted signal response from other
> > > directions.
> > >
> > > There is a little article about this on www.w8ji.com under receiving
> > > arrays, and while it deals mainly with 160 it also applies to other
> > > bands.
> > >
> > > The only time gain, or reduction of loss, helps is when the your
> > > system is limited by noise in the feedline or receiver.
> > >
> > > We need to compare pattern differences, rather than gain, for
> > > receiving. Odds are very good you won't see anywhere near the
> > > receiving S/N improvement that you see "gain" difference. many
> > > times a lower gain antenna system is a better receiving system
> > > than higher gain systems.
> > >
> > > Transmitting is another story, and even one or two dB can be major
> > > in how a weak signal sounds. A couple dB is actually well over one
> > > "S" unit marking on the meters of almost all receivers when signals
> > > are weak. Most receiver meters are very non-linear low on the
> > > scale.
> > >
> > > When you are weak, that two dB will seem more like several dB. If
> > > your signal is anywhere near strong, it won't mean anything unless
> > > you are in a pileup with other equally strong stations.
> > >
> > > Myself, I'd look at all options before changing the antenna!
> > > 73, Tom W8JI
> > > W8JI at contesting.com
> > >
> > >
> > > --
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> > >
> >
> >
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> >
>
>
> --
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