Bill, VLF,
A first test on 8970 Hz, audio propagation between my office PC and my
/p netbook was successful in the first attempt, without any calibrating
of a soundcard:
2012-01-30 21:54:33 >WOLF10 -r 24000 -f 8970 -t 1.0 -w 0.0000 -ut
21:54:57 f:-0.245 a: 1.4 dp: 19.3 ci:15 cj:254 ??????948???/CF ?
21:55:21 f:-0.244 a: 1.3 dp: 22.0 ci:15 cj:254 DK7FC JN49IK00 -
21:56:09 f:-0.243 a: 1.2 dp: 16.5 ci:15 cj:254 DK7FC JN49IK00 -
...Now i'll aply this signal to the PA.
Maybe i actually will use the DDS (drifting some mHz) and a CD4070 XOR
gate to toggle the phase. Then, i prevent phase glitches coming from
the soundcard.
If all works well i will start a first test on 8970 Hz using my fixed
antenna tonite or tomorrow. 1 km distance should be no problem
at all. Maybe its time to ask local VLF receiving stations (DD7PC,
Michael Oexner, ...) for a receive test.
If i can manage to get some kV out of the LOPT then i could arrange a
VLF beacon running 24/7 (even during wind and rain).
Is there someone in EU/UK interested in a WOLF DX test from
Heidelberg? In contrast to LF it is very interesting for me since a
real message can be transmitted, regardless how long it takes. One has
just to wait until something appears ;-)
73, Stefan/DK7FC
Am 30.01.2012 22:33, schrieb Bill de Carle:
Stefan:
I wouldn't change the phase reversal time - if you announce to the
world you're transmitting WOLF-10 that means phase transitions can
occur only at exact multiples of 100 milliseconds - everyone's receiver
will make that assumption. Don't worry about sync-ing phase shifts to
the zero crossings of the audio waveform, let's see if your
computer-to-computer test works first. You can specify a relaxed
tolerance for the receiver: e.g. +/- 2 Hz away from the nominal carrier
frequency to allow for slightly different sample rates at Tx, Rx.
Ultimately for long term coherent integration both Tx and Rx must agree
on the timing but for a first test with a strong signal (just to see if
everything is working), you won't need that. For longer integration
times it is probably better to use a GPS-stabilized DDS to directly
generate the WOLF signal at the Tx end. I find sound card sampling
rates are stable enough for WOLF once everything has warmed up a bit.
It's not the small instabilities that will hurt, it's that the absolute
sample rate must be known accurately and entered to allow the Rx clock
to keep same time as the Tx clock. Did you download that .wav file I
made last night? I intended that only for testing your Tx to see what
the sidebands look like with no waveform envelope shaping. Don't
expect anyone else to copy that message unless your sample rate is very
close to 24000 s/s and the signal strength at the 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 actually make sense to change
the phase reversal time? Since the samplerate is drifting anyway, there
will be a small time difference between a phase shift and there
zero-crossing. Also -if the samplerate would be exactly 24 kS/s-, the
time when the phase shift occurrs can be somewhere, i.e. wouldn't be
sync'ed to the zero-crossing. Right?
So it may be easier (also for the receiving side) to let it remain at
0.1 seconds.
Comments welcome.
73, Stefan/DK7FC
Am 30.01.2012 19:24, schrieb Stefan Schäfer:
Changed the phase reversal time from 0.1 s
to 0.111482720178372 s (=1000/8970Hz) Seems to work.
Am 30.01.2012 01:37, schrieb Bill de Carle:
Can your Tx handle abrupt phase shifts
every 100 msec? We can arrange for the phase shifts to occur only at
zero-crossings of the 8970-Hz sinewave.
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