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I agree with these comments, and have said it
before.
If all radio amateurs on all the other bands used this
system of uh bandwidths and day long qso's Amateur Radio would cease as a
hobby.
The aim should be to generate enough ERP so that a
qso could take place in a reasonably short time and be observed by others in say
QRS 3 - 60. SWL listeners/viewers could also particpate.
The Dreamers band will fizzle out if transmitted
signals are not improved so that a larger audience can engage in the
activities.
also who is going to buy a PCM2900 or similar gadgets
for a ONE OFF QSO if you are lucky.
Again QSL reports on frequency alone are not VALID - it
could be any carrier.
G3KEV
----- Original Message -----
Sent: Tuesday, March 08, 2011 8:42
PM
Subject: LF: VLF Stability and soundcard
locking
It would appear that a typical soundcard isn't stable enough for VLF
use when stations are running 1mHz bandwidth signalling, and using any locking
option to other off-air signals is a bit restrictive in what software you can
run.
It may be worth looking at a custom codec driven from a locked frequency
source. The PCM2900 (which costs only a few pounds from
Farnell, and they supply the data sheet) is a self contained USB codec which
needs only a handful of additional components for a USB soundcard with stereo
line input and output. For normal operation it needs a
12MHz crystal, but an external 12MHz source can be used which could be
locked to, or derived from, a high stability reference. Even a TCXO on
its own with typically 1ppm accuracy / stability would be better than any
normal 20ppm crystal
I've built one of these codecs, but have yet to confirm the
resulting sampling rate(s) are exactly what
they should be. By the time it has gone through USB packetising and
Windows' drivers I hope full synchronicity is maintained right through
to the user software. This may only be the case for sampling rates
like 12000Hz - it all depends what windows does. Exact conversion
is needed for this solution to be worthwhile, not just a close
approximation.
Andy
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