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[linrad] 40 kHz of bandwidth with NO extra PCI-cards; adapting output sampling (CPU-load); optimum frequencies; Mini-ITX
Mayday-Mayday to all (its the 1st of May)!
Actually the situation is not catastrophic at all, on the contrary.
I managed to initiate the ASUS A7V133-VM micro-ATX motherboard for
'Linrad' operation WITHOUT any extra PCI-boards under Knoppix 3.8.1
and the latest svgalib 1.9.21 and lir01-33. It means that a 40 kHz
segment of anyone band can be monitored effectively with extremely
good noise-canceling features, and cheaply, if dynamic range is not
the major concern. This is especially an optimum solution for a one
station 50 MHz DX-pedition in a remote DXCC-location (and anywhere
else for that matter). I posted a related note on the UKSMG-site.
Using the integrated audio is a good cost-saving feature. And it
would be nice to be able to use its full bandwidth, which is now
2 x 20 kHz typically with an I/Q-scheme in the 'Linrad'-receiver.
Regarding the CPU-load I would like to ask Leif/SM5BSZ, to comment
whether a slight modification of the Lagrange-interpolation could
work. Since most boards and integrated audio have coupled sampling
rates (48000/48000), would it be possible to prepare the D/A-output
bit-streams with modifications that could alleviate the workload of
the CPU? More specifically: would it be feasible to replace output
samples with strings of plain zeros thus mimicking 6000 and 8000 Hz
output rates? Example: output rate 48000 Hz, target 8000 Hz >>>>
calculate Lagrange-interpolation, feed to D/A-converter, fill next
5 samples with plain "0", then calculate the new D/A-output value.
Thus effective output rate will fall to 8000 Hz. Possibly the only
side effect with regular audio would be that the output level will
drop accordingly (and maybe an extra output filter is needed).
My proposal to the UKSMG (50MHz) is attached below. Given the nature
of the frequency spectrum, the radiation of noisy wiring, and the
commonly used antenna patterns, I think that the noise-cancelling
properties of 'Linrad' (regarding man-made "spikes") is best in
the 25 - 200 MHz range and not negligible in other parts of the
spectrum either. I have not yet tried the tiny VIA EPIA Ultra
Compact fanless Mini-ITX boards, but the used level of processor
performance should be sufficient to run a 48 KHz sampling solution.
Most of those have integrated SVGA and Audio, and room to add one
PCI-card, which could offer the 96 kHz 24-bit audio for instance.
The bands are opening up for Summer Es, so we would need all of
this any minute and preferably as a dedicated one-band solution.
73, "Zaba" OH1ZAA/2
Posting to UKSMG (www.uksmg.org)
Proposing UKSMG Project 'Linrad' for DX-peditions: Anyone interested in
top-notch receiver performance should read the following article:
http://www.sm5bsz.com/linuxdsp/qex/040102qex020.pdf ..... if you are not
familiar with the 'Linrad' subject, then it is advisable initially to "read
between the lines" (and particularly: to read the Conclusion).... The big
DX-peditions with maximum antenna size and power (W6JKV-style, etc....) are
typically heard by many stations, but during those happenings there are
many circumstances and periods during which the smaller home stations
(below 100 W power or equipped with small antennas) are not easily copied
at DX-pedition's site..... This could be helped with 'Linrad'-technology,
especially in the usual environments where there is a lot of man-made
interference due to a poor power-grid or nearby industrial activity and
faulty electric home-equipment or sparking traffic ---- Though the title of
the 'Linrad' article mentions High-Performance Hardware, it is especially
the (man-made) noise-canceling feature that can be fully implemented with
very inexpensive hardware.... Therefore I suggest that the UKSMG could
assemble a couple of these units that could serve thousands of stations, by
allowing the DX-pedition to hear the weakest signals from under the local
clutter (this means that copy below a certain input signal level can be
constantly ZERO without 'Linrad') ---- The equipment needed is a simple
micro-ATX motherboard fitted with the cheapest possible modern CPU running
'Linrad' under Linux..... I just hit an older ASUS motherboard with an
integrated SVGA-chip and integrated audio, that needs NO extra cards to
perform the monitoring and de-noising of one full 40 kHz band-segment (at
one time, i.e. one center frequency), together with a simple front end....
All that is needed is a regular 50 MHz preamplifier, a crystal oscillator
(as many as one needs for the number of band-segments), an I/Q-mixer, and a
few audio op-amps to prepare the signals for the MB's sound input.... The
cost of one package (including the PC, tiny barebone?) could well stay
under 500 dollars.... Any major 50 MHz expedition should be able to take
one of these with them, unless they already have their own system, which is
anyway usable anywhere and suggested for 24/7 dedication at home stations
as well.... I foresee a quick spreading of this technology among the
serious DX-ers taking no chances while new DXCC-countries are activated....
Wishing you luck with your personal experiments! ---- 73, "Zaba"
OH1ZAA/OHoMZA ["The sky is no limit"] ----
<http://www.uksmg.org/mailform.php?postno=6346>\"Zaba\", OH0MZA - Sunday,
May 01 2005 at 08:49 (GMT)
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