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RE: RE: 38k4 Operation with FT 847


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.


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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