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Re: My preamp coming out...



Hi Hasan, N0AN

If I know what is the difference between Noise Figure and Gain I can
understand your explanation otherwise I cannot.

Try to explain it in simple words please.

Tnx

73" de

i8CVS Domenico

----- Original Message -----
From: "hasan schiers" <schiers@netins.net>
To: "Luc Leblanc VE2DWE" <lucleblanc6@videotron.ca>; <amsat-bb@amsat.org>
Sent: Wednesday, March 22, 2006 10:56 PM
Subject: Re: [amsat-bb] My preamp coming out...


> Luc, (if I understand your post correctly)
>
> 1. An S-meter change is not the appropriate measure of the effectiveness
of
> a preamp.
>
> 2. The fact that your S-meter went full scale both at the antenna and at
the
> radio means nothing. Absolutely nothing (other than it has gain).
>
> 3. The preamp was designed to have a low noise figure (let's say < 1 dB).
> When you mount it at the antenna you get the benefit of that low noise
> figure. When you mount it at the radio, you add the loss of the coax to
the
> noise figure of the preamp. Typically, you might see 2.5 dB loss in your
> feedline at 70 cm. for normal lengths of coax (80'). Now this nice fancy
low
> noise preamp has a noise figure of 3.5 dB (which stinks), due to the
> additional loss of 2.5 dB from the coax in front of it.
>
> Unless you have VERY low loss in your feedline run, the preamp belongs at
> the antenna.
>
> For a proper analysis of this issue, it would benefit everyone to look at
> Gene's satellite link budget analysis spreadsheet, which evaluates the
> effects of antenna gain, sky noise, preamp noise figure and gain, feedline
> losses, receive bandwidth and front end noise figure of the radio. Just a
> few minutes manipulating the values in the spreadsheet and seeing their
> effect on receive sensitivity will demonstrate convincingly WHY a preamp
> belongs at the feedpoint, and WHY preamp gain is of only minimal
importance
> compared to noise figure.
>
> Noise figure (and overall system noise temperature) is the ONE variable
that
> absolutely must be paid attention to, when it comes to weak signal work.
> Assessments based on S-meter readings are worthless and worse, often
> misleading the casual satellite operator.
>
> If a person has any interest at all in learning about how your satellite
> receive system works, and how to optimize it, Gene's spreadsheet (Excel),
is
> an indispensible and informative tool.
>
> 73,
>
> ....hasan, N0AN
>
>
> ----- Original Message -----
> From: "Luc Leblanc VE2DWE" <lucleblanc6@videotron.ca>
> To: <amsat-bb@amsat.org>
> Sent: Wednesday, March 22, 2006 1:02 PM
> Subject: [amsat-bb] My preamp coming out...
>
>
> > Yes i make my coming out...
> >
> > I was not a preamp fan. I was not beleiving too much in preamps virtue
but
> > i should now getting out
> > the closet in admitting that i try a hamtronic LNG 432 on a SO-50 near
> > overhead pass.
> >
> > Results:
> >
> > From a RX signal who was never indicated on the FT-847 meter i was able
to
> > get a S9 plus 60db on
> > the same meter!! (still tryng to figure out the problem..) I quickly
> > installed the preamp at the
> > transceiver not even at the antenna and i got this result.?
> >
> > Many folks always recommend to install the preamp at the antenna feed
> > point to acheive the best NF
> > figures but when you got a full led scale i am just asking why should i
> > put the preamp there?  to
> > be battered by the WX ?
> >
> > With the official spring start yesterday it will be now possible to make
> > further test but it is
> > still hard to believe how much amplification this little box can do. I
> > have also an other one in
> > standby on VHF just awaiting to be tested too.
> >
> > For those who are thinking that my FT-847 is probably deaf or dead i
just
> > checked it with a cushman
> > signal generator and he is better than the Yaesu specs.
> >
> > Too bad for suit sat it will be an excellent source of weak signals.
> >
> > A former preamps unbeleiver...
> >
> >
> > "-"
> > "It is not the class of license the amateur holds, but the class of the
> > amateur that holds the
> > license."
> >
> > Luc Leblanc VE2DWE
> > AMSAT 33583
> > Skype VE2DWE
> > www.qsl.net/ve2dwe
> > ----
> > Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT member? Join now to support the amateur satellite program!
> > To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
> ----
> Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
> Not an AMSAT member? Join now to support the amateur satellite program!
> To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org
----
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