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Test Tools for determining ao-40 RX performance



All,

I've followed the discussion on NF and RX performance for some time.  I've
also been one of the lucky ones that came up with a pretty good RX setup
from the start.... I won't say it's on the cheap side, but it works pretty
well.  I'll explain that setup and some changes I'm going to make in a
moment, but first I wanted to offer some observations.

When I first started listening to ao-40, I built my system with anticipation
that we'd get access to the V uplink and so I used 432 as the IF for my
downconverter.  In retrospect, this had good and bad benefit.  The Good was
I spent the first month listening to ao-40, capturing telemetry and reading
all the posts about RX performance and comparing them to mine.  As some of
you know, I've shared my performance live on the net with both streaming mp3
audio and live telemetry.  The Bad was, I was unable to use the transponder
:(.

Well, Saturday I remedied that problem by replacing the 432 IF with a 144
IF.

What I've noticed in doing a months worth of SWLing on the bird.

- yes, there are people that are running modest setups with medium to high
noise floors that are making contacts.  But for each of those, I've heard
time after time, people calling them after a contact that they obviously
can't hear.  They finish the contact they just made and start calling CQ,
right on top of people that are trying to work them.
- yes, there are people who can't hear their downlink and turn up the power
until they can.  It's pretty amazing to watch the level of ones signal come
up when this happens.  I'm assuming, that they turn up the power to the
point where they can hear it and hope that everyone else can and that leila
doesn't get them :)
- the most interesting, is the mode where you crank up the power till Leila
gets you, then you back it down, until just under.  And that is where you
setup and operate.  What ever happened to the "use the least amount of power
appropriate to make the contact" rule of amateur radio :).  BTW, this mode
always produces, "Leila - Gotcha", it gets you right when you are trying to
exchange that grid square.

Now let me offer some more tidbits of information towards system setup.

- Not only is it RX performance, but it's also TX performance to some
extent.  You have to think about this, not in the context of turning up the
power, but more in the context of system performance to get an adequate
EIRPC for the bird to hear you.  For example, here is what I'm stuck with.
I have a system where I have about 185' of 9913 between my station and my
antennas.  (It has to do with trees, towers, etc.)  Saturday, while I had
everything apart working on the DC exchange, I decided to check the power to
the antennas.  For 50W of output on the TS2000 to the 435 Antenna, I had a
whopping 10W.  For 100W of output on 144, I had 37W of output to the
antennas.  See where this is going.... Improve both your setups and that
doesn't mean adding more "amp" unless that is the only way.

- On RX performance....I continue to read people saying "I make contacts, so
I think my setup is good enough".  Well, it might be for you, but understand
what you present for others with better system as I discussed above.  I'm
not advocating that everyone go out and buy top of the link equipment, I'm
just providing some insight.  If you can't hear the transponder noise floor
at apogee, you are missing *lots* of signals.  I'll offer a case in point.

I was all excited to get my system on the air on Saturday night after the DC
change.  Pieter - N4IP lives pretty close to me and he runs a 4.5' dish on
the downlink.  The "unqualified" difference between his system and mine is
usually 2 Sunits.  If I'm hearing S3 - he usually hears S5.  Our performance
is "pretty close"... But I'll tell you, I can't hear the Transponder NF.
The sat was at apogee Saturday night when the transponder came on over the
Eastern US.  We first established that I could get into the sat and hear
myself... All whopping 10W of power to the antennas and all.  We were
coordinating on IRC (btw, for those that want to check out your system, I
would encourage you to get on there, you'll get a real feel for what others
are hearing vs. your setup).  We next started looking around the band.
There were some DL's, and some other Europeans on.  I made a couple of
contacts and then Mark Hammond came up on the IRC an wanted to test his 1.2
and 435 uplink/downlink setup.  So we worked to figure out everyone DC
offsets and found common ground (always an interesting challenge with
doppler, differing DC offsets, etc).  I was hearing Pieter as one of the
loud ones.  I could hear a very faint carrier occasionally and through IRC
determined that it was Mark.  All of a sudden Pieter started to have a
conversation with him.  I couldn't hear squat!  I tried every combination of
filter I could think of on the 2000, but nada!  Bummer, my setup wasn't as
good as I thought.  But I do know how to fix it and I'll explain that later.

I just read an email from Hasan that I hope everyone takes to heart.  Just
remember one thing.... Just because you can hear yourself, doesn't mean you
can hear what's on the bird!  That's really the bottom line.  Get on the IRC
channel and work with some of us to test your system and make some
comparisons.  We are all experimenting and trying things, some us are
throwing $$$ after it and others aren't.  We'll all have to accept
compromise, but we should all work to as optimum of a system as we are able.

I've found some tools that might help in making test.  There is a pretty
good tool from the guys in DE, that can be used with a sound card to measure
all kinds of things with radios... SNR is the most useful, but there are
others as well.  It's called Analyzer 2000.

Between this software and a calibrated Smeter and the "spreadsheet", you
should be able to measure a "relative" system performance.  I've included
the link below.  Just as a note, it is shareware.

http://www.brownbear.de/

Ok, back to some changes that I'm going to make to try to improve my RX on
2.4.  I can't run a dish at the top of an 80' free standing crank up tower,
so I'll have to make some long term compromises.

My current setup
1 - DirectiveSystems.com 1252 - 52 element loop yagi on an 8' boom, 21dbi
(linear - horizontal)

10' of 9913 to the downconverter, this is scary, because 9913 at 2.4 has
almost 7db/100' loss.  So a 10' section is almost 1 db taken directly away
from the DC's input :(

SSB UEK3000SAT Downconverter - .7db noise (this isn't a 2000, it's a 3000
and they spec it at .7 instead of .8 on the 2000) with 30db of gain

180' of 9913 to get back to the shack... Again a compromise, but this
doesn't show as bad on the RX side of the DC...

Kenwood 2000 with an evaluated NF of 5 @ 2100hz bandwidth

Spreadsheet number on the above. 63000km, 15 degrees of squint
system NF = 1.4
MDS = -144.9
Beacon S/N = 17.4

My new setup will be
2 - DirectiveSystems.com 1252 - 52 element loop yagis, stacked vertically
with a Directive systems power divider - cross your fingers, 24dbi (still
linear horizontal).  this is *way* less wind loading than a dish, and what
I'm going to run for now.

1 - DEM 2.4G preamp attached right at the antenna (should remove that .7db
of loss from the 10' of 9913)

10' of 9913 between the DEM and the UEK.  I'm hopeful that the 17db of gain
in the DEM will make up for the .7db of loss at 2.4 with the 9913

Rest of system unchanged.

Spreadsheet number on the above. 63000km, 15 degrees of squint
system NF = .6 (-.8)
MDS = -148.8 (-3.9)
Beacon S/N = 22.8 (+5.4)

For me, this will be about as good at it gets....Course, I could always
think about stacking 2 more 2.4's for an additional 2.5-3db :)..... Nah!!
Maybe, I'll figure out a way to create a phasing array for circular
polarization of this combination.... that would be work 3 more db... In
theory.

My .05 for what it's worth!
Alan

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