From the BBC news ,
''The phenomenon, known as a perigee full moon, means the Moon appears up to
14% bigger and 30% brighter than when it is furthest from the planet.''
They go on to state :-
''Scientists have dismissed the idea the perigee could cause strange
behaviour - like lycanthropy - or natural disasters.''
As yet another 'Dog fight' breaks out, Obviously are not monitoring
Black sheep then ?
G..
--------------------------------------------------
From: "mal hamilton" <[email protected]>
Sent: Sunday, May 06, 2012 6:27 PM
To: <[email protected]>
Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?
Does Pipe Dreamer ring a bell !!!!
----- Original Message -----
From: "Roger Lapthorn" <[email protected]>
To: <[email protected]>
Sent: Sunday, May 06, 2012 4:58 PM
Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?
Mal, you are talking rubbish again.
Without frequency locking in SL and very very narrow bandwidths possible,
there is no way I would have been able to copy the EU VLF amateurs last
year
in this semi-urban noise pool. Not many of us live in v.quiet rural areas.
You may be able to copy VLF DX at QRSS3 but most of us can not at any
distance.
Regarding VLF activity in the UK, I continue to do earth-mode tests
although
I have been distracted to NLOS optical comms of late. Not sure if G3XIZ is
planning further radiated tests. Several stations including G3ZJO monitor
EU
VLF tests regularly.
73s
Roger G3XBM
-- Via my 2.4GHz transceiver --
On 6 May 2012, at 17:26, "mal hamilton" <[email protected]> wrote:
Andy
All these complications to accommodate the Appliance Operator who cannot
read MORSE or watch QRSS on a screen.
g3kev
----- Original Message -----
From: "Andy Talbot" <[email protected]>
To: <[email protected]>
Sent: Sunday, May 06, 2012 4:14 PM
Subject: Re: LF: Generating 8970 Hz carrier with Spectrum Lab ?
The problem with USB slippage comes about because of the Isochronos
mode (yes, that is spelt correctly, it is not IsoSYNchronous) -
where it sends puts real time rapid data transfer as more important
than lost samples and sends samples in real time without checking
This is probably just what music and audio people want, but it screws
up using USB based sound cards as precision timed A/D converters.
USB does have other modes with full error checking, albeit with some
latency, but the latency wouldn't matter here.
While it would be a pretty simple task these days to build an external
A/D converter and interface to USB properly, the resulting data stream
would need a custom driver written, then all the decoding software we
know and love would have to be modified to work with this custom
interface. Then someone else would come along with another design
and we'd have to start again.
I suspect it is going to be absolutely impossible to use the soundcard
as a guaranteed glitch free A/D converter.
Joe Taylor K1JT in the WSJT suite has a dead simple pragmatic
solution. Instead of trying to read the data in real time, all the
WSJT modes read the entire transmisisons' worth of data to a .WAV
file, and the software works on that. While WSJT uses the soundcard
to do the job it will suffer from the same slippages (which don't
matter' of course' for those modes) the idea of an intermediate buffer
file would help.
A custom A/D could send its data in its own format via USB, or serial
COM port or whatever, to software that saves blocks in the format of a
.WAV file. Then the decoding software works on the resulting .WAV
files. It won't be real time any more, but none of these slow data
modes actually are that real time. The speed of reading and switching
(using a pair of ping-pong files if necessary) can make the whole
system pseudo real time - in the same way as WSJT appears to run
continuously.
Now, any A/D design can be used provided the results are written to a
.WAV file. Wav files can have any sample rate (so long as it is an
integer number of Hz) and do not have to be restricted to 48000, 11025
or whatever, so custom LF receivers using quite slow A/D converters
and low sample rates are now valid.
Just throwing that idea into the ring..
Andy
www.g4jnt.com
On 6 May 2012 16:14, James Moritz <[email protected]> wrote:
Dear Andy, LF Group,
A bit late, but never mind...
Has anyone tried using an external USB soundcard with a separate
locked clock? Most work from a 12MHz crystal which can be replaces
with a GPS locked source without too much effort. But I can't help
wondering if there will be subsequent USB synchronisation glitches
upsetting the input sampling.
I can confirm that glitches do occur with USB sound cards. I have found
this
to be a perennial problem trying to use such a sound card with the
laptops
I
have available. For 9kHz reception, the relatively rapid temperature
fluctuations inside the laptop, and resulting cyclic drift of the
internal
soundcard sampling frequency interfere with the operation of DL4YHF's
ingenious sample rate correction facility in SpecLab, making the
internal
sound card unusable for FFT resolution below a few millihertz. I found
my
USB soundcard solved this particular problem quite well, but introduced
glitches that made achieving FFT resolution in the uHz range
impractical.
Watching Speclab's sample rate correction "history" window, the USB card
sample rate typically starts off a few hundred ppm low (much larger than
the
actual clock frequency error), but remaining stable to within a few ppm,
but
then at unpredictable intervals abrupt jumps in sample rate of a similar
order of magnitude occur, with corresponding "blips" on the spectrogram
traces. The reported sample rate is always lower than the nominal value,
suggesting that some samples are being periodically discarded somehow.
The sound card uses a single-chip integrated audio codec and USB
transceiver, using a single 12MHz crystal. I can't really believe in
"USB
slippage" in the hardware - surely losing some of the data would either
be
handled quietly by the USB error checking, or result in endless error
messages. The same sound card seems to work in a glitch-free way when
plugged into my desktop machine, where the reported sample rate error is
in
line with the error in the crystal frequency.
Cheers, Jim Moritz
73 de M0BMU
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