Topband: Re: [CQ-Contest] Re: Topband: TOP BAND RECEIVING ANTENNAS

[Marijan Miletic, S56A]

Having consulted OC Matjaz, S53MV, I must make the following correction:

Directivity has NO influence on received isotropic noise power.

Received signal to isotropic noise ratio is therefore independent of the
efficiency of directional antenna.

73 de Mario, S56A, N1YU

----- Original Message -----
From: "Marijan Miletic, S56A" <artinian at siol.net>
To: <W8JI at contesting.com>; <i4jmy at iol.it>
Cc: <topband at contesting.com>; <cq-contest at contesting.com>
Sent: Tuesday, January 08, 2002 8:22 PM
Subject: Re: Topband: Re: [CQ-Contest] Re: Topband: TOP BAND RECEIVING
ANTENNAS


> > It is almost certainly NOT based
> > on a very directional antennas, in particular inefficient antennas,
> > since the more directional the antenna the lower the noise level is.
>
> We assume that atmospheric noise is evenly distributed in the space around
> us.
>
> Very directional and efficient antenna will exibit high gain and pickup
that
> much MORE noise.
>
> Inefficient antenna will get proportionally less noise in the linear
> fashion.
>
> There seems to be a confussion between noise and QRM from the unwanted
> direction.
>
> Any modern RX has preamp and attenuator.  Later should be more often used.
> Even for TX clicks :-)
>
> 73 de Mario, S56A, N1YU
>
> ----- Original Message -----
> From: "Tom Rauch" <w8ji at akorn.net>
> To: <i4jmy at iol.it>
> Cc: <topband at contesting.com>; <cq-contest at contesting.com>
> Sent: Tuesday, January 08, 2002 5:48 PM
> Subject: Re: Topband: Re: [CQ-Contest] Re: Topband: TOP BAND RECEIVING
> ANTENNAS
>
>
> >
> > > gets well alive when connected to the antenna. Playing with N stacked
> > > beverages (1 to 2 WL beeing probably best choice) insures a good
> > > pattern control and offers an output level that surely meets or exceed
> > > PY5EG system needs. I agree that antenna preamplifiers should be
> > > avoided when it is possible.
> > >
> > > 73,
> > > Mauri I4JMY
> >
> > The old argument or idea you never need an amplifier is just as silly
> > as saying you always do need an amplifier.
> >
> > I would guess the "rule" we never need -140dBm sensitivity is
> > based on a suburban location, perhaps with a wide filter, or
> > perhaps a very efficient antenna. It is almost certainly NOT based
> > on a very directional antennas, in particular inefficient antennas,
> > since the more directional the antenna the lower the noise level is.
> >
> > Suggesting people always do NOT need an amplifier or a very
> > sensitive receiver because we read it someplace is like telling them
> > they always DO need one. Both are very wrong, because the
> > circumstances vary greatly!
> >
> > There is one rule that always works.
> >
> > Set your gain with use of preamplifiers or attenuators so you can
> > just comfortably hear a noise increase when the antenna is
> > connected, and a definite decrease with it removed.  If your receiver
> > can not take you comfortably into the noise without overloading on
> > the strongest 160 signals, then you need to buy another receiver or
> > have your receiver repaired...or give up working some weak signals.
> >
> > My web page covers this in detail.
> > 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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