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38k4 Operation and equipment modification sense



This has been a very good discussion and I appreciate all the thoughts and
comments. 

What I really would like to know is what kind of discussion goes into the
decision making. In other words, why are we putting these functions in a
satellite when it requires heart surgery on a very expensive piece of
equipment and almost another $1,000 in additional equipment (IFD board, TNC
etc.). Yes, I certainly support and actively engage in experimental
approaches but where does this leave the "average" satellite ham operator?
Are we pushing this hobby to the limit, probably? Are we excluding more and
more active amateurs, probably? But maybe that's why it is called
experimenting and the 38K4 is only running once in a while.

I don't know, maybe I am off the wall, but certainly appreciate any
feedback. 

Thanks again for a great online discussion and sharing of experience. 

Stefan, KC8NSA/VE4



-----Original Message-----
From: owner-AMSAT-BB@amsat.org [mailto:owner-AMSAT-BB@amsat.org] On Behalf
Of Mark L. Hammond
Sent: January 24, 2005 12:43 PM
To: Howard Long; amsat-bb@amsat.org
Subject: RE: RE: [amsat-bb] 38k4 Operation with FT 847

Howard,

Nice testing setup!  I'm lucky to have an old 'scope that seems to work.
That pretty much sums up my needs and expertise, though :)

Did you run similar tests with the PCR-1000?

I guess I haven't moved from the 2-level digital approach (1=it works, 0=it
doesn't) into a 24/32/64/128 bit zone (precisely how well does it work?).
Maybe in time...

In the meantime, I am enjoying the updates/information about the SSETI
project.  It will be fun to try and help collect telemetry.

73,

Mark N8MH

> 
> From: "Howard Long" <howard@howardlong.com>
> Date: 2005/01/24 Mon AM 09:47:51 EST
> To: "Mark L. Hammond" <mlhammond@charter.net>,  "AL7CR"
>   <al7cr@punakea.com>, 
>         <amsat-bb@amsat.org>
> Subject: RE: RE: [amsat-bb] 38k4 Operation with FT 847
> 
> Hi Mark
> 
> > The good news?  The IFD "normal" board is good up to like 76k8,
> > so you'll be ready for that, too :)
> 
> The bad news about being 76k8 ready is that, depending on the receiver the
> IFD's connected to and the transmitter's deviation and filtering, you can
> lose 3 to 5dB of sensitivity compared with using the narrower 80kHz Murata
> MTE filters (as long as you can correct for Doppler).
> 
> Here's a small selection of some of the tests I've done in setting up the
> SSETI Express groundstation segment, using a 145MHz IF in all cases:
> 
> For 10^-3 BER, 38,400bps, SYMEK TNC3S
> 
> 1dB NF using preamp, AR-5000, MTE filters -113.7dBm
> 1dB NF using preamp, FT-847, MTE filters -112.8dBm
> 1dB NF using preamp, AR-5000, MTY filters -109.1dBm
> 1dB NF using preamp, FT-847, MTY filters -109.4dBm
> 
> In an attempt to reject any front end sensitivity issues, I use a Mutek
1dB
> NF preamp for all tests: I found that without this, the BER results were
> worse by about -5dB!
> 
> The test is achieved by feeding an HP8656B signal generator with a 12kHz
> deviation signal from the TNC in BER mode. The deviation and signal
strength
> are checked with an external Marconi 2955A comms test set. I have a
> Tektronix 2465BCT 'scope attached in counter mode. I repeatedly fire off a
> million bits (by manual timing - takes 26 seconds), adjusting the
amplitude
> of the signal generator until I achieve as close to 3,000 counts as I can
> get (one bit error produces three counts).
> 
> Make sure you conduct these tests when the YL/XYL is out...
> http://www.g6lvb.com/images/ber001small.jpg
> 
> 73 Howard G6LVB


 
Mark L. Hammond    [N8MH]
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