Date: Mon, 30 Jan 2012 16:33:35 -0500
To: rsgb_lf_group@blacksheep.org
From: Bill de Carle <ve2iq@magma.ca>
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Subject: Re: VLF: WOLF, next step..
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Stefan:
I wouldn't change the phase reversal time - if=20
you announce to the world you're transmitting=20
WOLF-10 that means phase transitions can occur=20
only at exact multiples of 100 milliseconds -=20
everyone's receiver will make that=20
assumption.  Don't worry about sync-ing phase=20
shifts to the zero crossings of the audio=20
waveform, let's see if your computer-to-computer=20
test works first.  You can specify a relaxed=20
tolerance for the receiver: e.g. +/- 2 Hz away=20
from the nominal carrier frequency to allow for=20
slightly different sample rates at Tx,=20
Rx.  Ultimately for long term coherent=20
integration both Tx and Rx must agree on the=20
timing but for a first test with a strong signal=20
(just to see if everything is working), you won't=20
need that.  For longer integration times it is=20
probably better to use a GPS-stabilized DDS to=20
directly generate the WOLF signal at the Tx=20
end.  I find sound card sampling rates are stable=20
enough for WOLF once everything has warmed up a=20
bit.  It's not the small instabilities that will=20
hurt, it's that the absolute sample rate must be=20
known accurately and entered to allow the Rx=20
clock to keep same time as the Tx clock.  Did you=20
download that .wav file I made last night?  I=20
intended that only for testing your Tx to see=20
what the sidebands look like with no waveform=20
envelope shaping.  Don't expect anyone else to=20
copy that message unless your sample rate is very=20
close to 24000 s/s and the signal strength at the=20
Rx is high enough to enable decoding within seconds, not minutes or hours.
Good luck!
73,
Bill VE2IQ

At 01:57 PM 1/30/2012, Stefan DK7FC wrote:
>Bill,
>
>Thought about the zero-crosings. Does it=20
>actually make sense to change the phase reversal=20
>time? Since the samplerate is drifting anyway,=20
>there will be a small time difference between a=20
>phase shift and there zero-crossing. Also -if=20
>the samplerate would be exactly 24 kS/s-, the=20
>time when the phase shift occurrs can be=20
>somewhere, i.e. wouldn't be sync'ed to the zero-crossing. Right?
>So it may be easier (also for the receiving=20
>side) to let it remain at 0.1 seconds.
>Comments welcome.
>
>73, Stefan/DK7FC
>
>
>Am 30.01.2012 19:24, schrieb Stefan Sch=E4fer:
>>Changed the phase reversal time from 0.1 s to=20
>>0.111482720178372 s (=3D1000/8970Hz) Seems to work.
>
>
>Am 30.01.2012 01:37, schrieb Bill de Carle:
>>Can your Tx handle abrupt phase shifts every=20
>>100 msec?  We can arrange for the phase shifts=20
>>to occur only at zero-crossings of the 8970-Hz sinewave.