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Re: VLF: EbNaut tonite, 'SMS' via VLF

To: [email protected]
Subject: Re: VLF: EbNaut tonite, 'SMS' via VLF
From: DK7FC <[email protected]>
Date: Tue, 30 May 2017 09:07:51 +0200
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Hi Markus, Paul,

It was a long transmission with relatively short symbols. Apart from the accuracy that is required for the timing there is also a higher requirement for the accuracy of the frequency. In my attempts of getting a decode from the recent 970 Hz test i saw that there is a frequency offset of -1/(transmission time) or probably rather -1/(FFT length). I'm still not absolutely sure but maybe this also plays a role here?
A frequency offset was also observed by RN3AUS. Maybe this is not
propagation but an effect that happens in the SL instance?
Something we can find out in coming transmissions.
I could run something like 30...40 characters, which is close to the limits for SQ5BPF and DL0AO...
73, Stefan


Am 29.05.2017 19:58, schrieb Paul Nicholson:
Markus wrote:

> I managed to produce a seamless wav with 0.514 Hz samplerate:
> http://df6nm.bplaced.net/VLF/fec_tests/dl0ao_170524-25_join31uHz_wav.zip
Still no decode.  The correlation peaks at 20.44 dB in 12.6 uHz with
offsets +2058 seconds and +0.1 Hz so it looks like the settings are
correct.    I'm using the sample rate 0.5143924/sec from the
WAV inf1 header.

It's about 9 or 10dB short of decoding.

The previous attempt gave 22.09 dB in 12.6 uHz so it's lost a
couple of dB somewhere.

--
Paul Nicholson
--





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