[CQ-Contest] Re: 2 dB more?

Mon Dec 31 18:13:15 EST 2001

We use antennas in a system, in an environment, not in free space.
Therefore antenna system design and system performance (gain/directivity) is
just the matter to consider.
HNY!

73,
Mauri I4JMY

----- Original Message -----
From: "Marijan Miletic, S56A" <artinian at siol.net>
To: "Maurizio Panicara" <i4jmy at iol.it>; <cq-contest at contesting.com>
Cc: <Matjaz.Vidmar at fe.uni-lj.si>; "Tom Rauch" <w8ji at akorn.net>
Sent: Monday, December 31, 2001 5:31 PM
Subject: Re: [CQ-Contest] Re: 2 dB more?

> 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
> > > >
> > > >
> > > > --
> > > > CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
> > > > Administrative requests: cq-contest-REQUEST at contesting.com
> > > >
> > >
> > >
> > > --
> > > CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
> > > Administrative requests: cq-contest-REQUEST at contesting.com
> > >
> >
> >
> > --
> > CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
> > Administrative requests: cq-contest-REQUEST at contesting.com
> >
>

--
CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST at contesting.com