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R: AO-40 spreadsheet



Hello Hasan,

Why dont add the received sun noise as a reference of our receiving system ?
Measuring  sun/sky and ground/sky noise as described in Bob Atkins,KA1GT
article "Noise Temperature,Antenna Temperature and Sun Noise" is very easy
and this article has been published in The ARRL UHF/MICROWAVE
EXPERIMENTER'S MANUAL

My system sun/sky (S+N)/N is 5 dB at 2400 MHz  and under this conditions i
get the AO40 transponder noise at apogee with at least  3 dB of (S+N)/N or 0
dB of S/N but normally much more.
If i get a sun noise (S+N)/N=3 dB i must be happy because any increase of
antenna gain or any reduction of the overall receiver noise figure is not
necessary.

If any of my friend do receive the same sun noise he should be happy to
because under this conditions the ability of my system on receiving weak
AO40 signals cannot be improved.

If tomorrow i get less of 5 dB of sun/sky noise i must be unhappy and i need
to investigate if  the solar flux is decreased or something is wrong with my
antenna or receiver.

Sun noise test is very simple and is widely used by EME operators to
establish for reference if they are in condition to receive their own echo
off the moon or not only by using an AC voltmeter directly connected to the
receiver audio output.

73 de i8CVS Domenico


----- Original Message -----
From: hasan schiers <schiers@netins.net>
To: Gary Mayfield <gary_mayfield@hotmail.com>; <fspinner@hotmail.com>;
<amsat-bb@AMSAT.Org>
Sent: Sunday, May 27, 2001 3:29 PM
Subject: Re: [amsat-bb] AO-40 spreadsheet


> Hi Gary,
>
> If you have a converter with a good noise figure and adequate gain, as
well
> as an antenna with sufficient gain, you'll do fine.
>
> A 5 dB NF with a 21 dBi linear antenna is not adequate, no matter what a
> person thinks they are hearing.
>
> It isn't about cost, model, or anything else.
>
> On one side we worry about "scaring" people with system requirements too
> high.
>
> On the other side we have alligators. The trick is finding the best middle
> position one can construct.
>
> People can convince themselves of whatever they want to...I've done it
many
> times myself. The one thing that is indisputable is that until you can
hear
> at least a dB or 2 of satellite passband noise at apogee, you haven't hit
> the ideal. Is this required? Of course not. Is it desrable? Yes. How close
> each of us comes to it, will improve the transponder's performance for
> EVERYONE, especially the weaker stations.
>
> It isn't "my NF is better than your NF". If anything, it's "my MDS is
better
> than your MDS", if people must be competitive. The real question is, "Is
my
> MDS good enough?"
>
> How do we determine what is good enough?
>
> Here are some (silly)  criteria in rank order:
>
> 1. I hear at least 1 dB of passband noise at apogee with 0 squint.
> 2. I hear nearly every person on the bird, even the weakest stations.
> 3. I hear most everyone, and I sound pretty decent myself.
> 4. I hear only the strongest signals, and I'm OK if I crank the power up
> enough
> 5. I only can get others to copy me if I crank my uplink through the roof.
> 6. I hear a few others, but my signal stinks.
> 7. I trigger Liela when I try to hear myself.
>
> As I've said before, we have been through this situation several times
> before. The rules don't change. The poorer you hear, the more selfish you
> must be in order to use the bird. It's unavoidable. The goal should be to
> hear as well as you possibly can. This provides the maximum benefit to
> everyone.
>
> It doesn't matter how we do it...but it needs to be done. It's not about
> being scared. It's about the nature of receiving weak signals at this
> frequency. We don't help people with a "this will get you by" approach. We
> need to understand what it is the best that can be achieved and how far
> short of it we are. Then investigate how to get there, or as close as
> possible, given our skill, finances, et al.
>
> The nice thing about the tool that Marcus has given us is that we can
plan,
> evaluate and change. For example:
>
> You think your downconverter and antenna are doing really well. Measure
your
> actual S/N ratio on the beacon and compare it to what kind of system would
> produce that S/N in Marcus's program. This requires nothing more than a
> calibrated attenuator...MFJ sells a really nice one for all of 69 bucks.
> S-meters are worthless for this purpose unless they have been calibrated
> with an attenuator on the band of interest.
>
> You can prove to yourself how well you system is working (forget about
> signals on the bird). Measure the SNR you are getting on the Beacon at a
> particular point in time, plug those numbers into the spreadsheet and see
> how your system is "really" working. It's a neat, and revealing
experiment.
>
> With a system NF of .8 dB, the Beacon SNR should be 26 dB
> With a system NF of  3 dB, the Beacon SNR should be 21.1 dB
> With a system NF of 5 dB, the Beacon SNR should be  18.0 dB
>
> Since the STRONGEST STATION is supposed to be no more than 8 dB BELOW the
> beacon:
>
> Strongest Station:
>
> NF: 0.8 = 18 dB SNR
> NF:    3 = 13.1 dB SNR
> NF:    5 = 10.0 dB SNR
>
> This means at a NF of 5, the strongest station will only be 10 dB above
your
> noise floor. That leaves only 10 dB of dynamic range for you to hear other
> stations. The classic alligator.
>
> We should look for balance in our approach. We are unlikely to achieve the
> ultimate, but we shouldn't settle for guessing.
>
> 73
>
> hasan schiers, NØAN
> schiers@netins.net
>
> ----- Original Message -----
> From: "Gary Mayfield" <gary_mayfield@hotmail.com>
> To: <schiers@netins.net>; <fspinner@hotmail.com>; <amsat-bb@AMSAT.Org>
> Sent: Sunday, May 27, 2001 6:55 AM
> Subject: Re: [amsat-bb] AO-40 spreadsheet
>
>
> >
> > >
> > >The original "illusion" that these 20 or 30 buck converters with a bbq
> > >grill
> > >antenna system were going to work just fine has been shattered. There
> >
> > Is this really true?  I've been quite happy with mine, and I've made
quite
> a
> > number of QSOs.  I think it is more a case of "my noise figure is better
> > than your noise figure".  I seem to hear everyone who is on.  I'm sure
> they
> > are closer to the noise than where some other folks hear them, but once
> you
> > can hear them good enough to work them how much more signal do you need?

> If
> > you can copy your own signal well, and don't trip LEILA is that
> acceptable?
> >
> > I have a fear that we will scare more people by implying that you need
> > either:
> >
> > A) a really big investment to get on S-Band (The complaint I already
hear
> > the most)
> >
> > B) the skill of a neuro-surgeon along with $250 K of test equipment.
> >
> > 73,
> > Joe
> > ka0yos@amsat.org
> >
> > _________________________________________________________________
> > Get your FREE download of MSN Explorer at http://explorer.msn.com
> >
>
> ----
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>






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