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RE: RE: 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...

73 Howard G6LVB
Sent via amsat-bb@amsat.org. Opinions expressed are those of the author.
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