[CQ-Contest] Re: 2 dB more?

[Maurizio Panicara]

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
> >
>
>
> --
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>


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