Hi Jim and all,
The 1 kHz filter sounds like a good idea. If you don't have
strong carriers dominating the audio, then 8 bit samples should
be fine. Also, if you keep the audio frequency fairly low,
you can record at, or convert to, a lower sample rate. If you
will be downsampling with software, please record the
original at 16 bit resolution, and convert to 8-bit samples
at the lower rate.
Fifteen minutes should be plenty. At 5512 bytes/sec, that's
about 5 MB, and it will probably zip to about 4. Even lower
sample rates should be fine if they don't lose data.
Alternatively, if you don't mind sending a CD-R to Paris,
then you need not worry about file sizes.
73,
Stewart KK7KA
----- Original Message -----
From: "James Moritz" <[email protected]>
To: <[email protected]>
Sent: Tuesday, April 23, 2002 4:35 PM
Subject: Re: LF: Re: Re Jason .WAV files
At 12:23 23/04/2002 +0200, you wrote:
>Unless there is strong QRM on an adjacent frequency, please use
>a wide (SSB) filter, and put the desired signal near the center
>of the IF passband. This makes it easier for impulse noise
>rejection algorithms.
>
>Thanks,
>
>Stewart
Dear Stewart, LF Group,
Using the usual "data" frequency around 137.5, the problem is the very
strong DCF39 signal on 138.83kHz. It is possible to receive in an SSB
bandwidth at my QTH, provided there are no local stations operating, but I
would have to have the filter bandwidth centered on about 136.5kHz.
Alternatively, I could use a 1kHz bandwidth filter. Another possibility
would be to use the "transatlantic" slot around 135.9kHz, but in this
case, the problem would be the Datatrack beacons off the lower band edge.
Do you have a preference for a particular sample rate? How long a recording
do you need? I can E mail a few megabytes without too much trouble, but if
you need longer I will have to get the data burned onto a CD and mail it to
you.
Cheers, Jim Moritz
73 de M0BMU
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