Re: LF: WOLF Again, ADC Dynamic Range

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Subject:	Re: LF: WOLF Again, ADC Dynamic Range
From:	[email protected]
Date:	Mon, 25 Apr 2005 16:26:51 EDT
Delivery-date:	Mon, 25 Apr 2005 21:27:32 +0100
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Dear John,

three blocks were decoded successfully in Nuernberg, at 01:23, 03:09 and 03:41 UT:

t:1920 f: 0.029 pm: 7 jm:665 q: -1.4 -4.6 XES WOLF 137441 -

Propagation appeared to be well above average, with both WD2XGJ and VO1NA visible in good quality between midnight and about 04:45 (see image below).

I could also decode these sections of your transmission from an all-night audio recording, decimated to 86.14 Hz samplerate at 8 bits, using the original DOS version of WOLF. At first there was not enough gain, "pm" stayed zero and "f" stuck to the lower tolerance limit (-0.2Hz). Recognizing your comment about audio gain, I then "hendrixized" the file by running it through the sndrec32 "louder by 25%" function several times, and voila, suddenly it decoded alright, with pm increasing in 3 to 5 unit steps. Apparently there is some threshold in Stewart's decoder, which does not allow it to recognize low-level signals, even if they would be well above the (quantization and other) noise.

However for live audio, I cannot increase the gain much here, as I have several strong signals in the full SSB passband needed for the grabber (SXV, DCF39 on the edge, DK1IS, DK7SU and others). Thus my ADC full scale is normally set to approximately 100 µV/m, with 16-bit digitizing.

Interestingly, experiments have verified that even an 8-bit soundcard setting gives more than adequate dynamic range. The quantization noise level would be
Nq = +40 - 8 * 6.02 - 1.76 - 10 log(11025/2) dBµV/m/sqrt(Hz) = -47.3 dBµV/m/sqrt(Hz),
still 20 dB below the minimum noise background of -27 dBµV/m/sqrt(Hz), observed on very quiet sunday mornings.

Are you really sure you want to go down to 15 Watts, and what is your ERP then? Well, we'll see what we can do ;-)

Good luck, 73

Markus

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