[linrad] Re: UKSMG / 50 MHz and low-VHF Linrad ; Re: [linrad] Linrad-02.14

[leif Asbrink <sm5bsz.com; leif@xxxxxxxxxxxxxxxx>]

Hi Zaba and all,

> As radio DX-peditions to rare spots very often hit environments 
> with a poor electricity network and a lot of interference sources, 
> it would be nice to have some ready dedicated hardware packages 
> to allow these expeditions to enjoy optimum reception during 
> difficult periods of the expedition. Possibly this would be an 
> eye-opener for some hardened experienced operators and thus an 
> inspiration for effective future VHF-operations.
A lap-top running Windows and an SDR-14 for hardware with suitable
pre-selectors and/or converters would be a light-weight solution
for all bands. Presumably powerline noise could be a problem on
lower bands also.

> Given the old times with "just" Linux and Linrad, I noticed 
> that with  the given time and energy I was generally spending 
> all my attention on the software. Then with time the knowledge 
> base (personal memory) is decaying and there is just so
> much that one remembers from the past "lessons" and documentation. 
> Generally I have seen about 1 second delay when starting Linrad 
> with default parameters and 48000 kHz sampling. Can you tell us, 
> Leif, what we give up in reception features if delays are reduced 
> to the values you mention in your May 27th comparison?
This comparison is an example of extremes. The baseband filter
is made from a short transform and therefore it has a modest
shape factor and a poor stop band rejection. The filter response
is plotted as the first image:
http://www.sm5bsz.com/linuxdsp/usage/ldfw/ldfw.htm

There is no noise blanker in this example but the blanker does not 
increase the delay much.

My own usage of Linrad in the past was focused on EME and signals
deep down in the noise. I was normally running at delays between 5 
and 10 seconds.

Please remember that Linrad is not an SDR - it is a tool-box by
which you build an SDR by selecting appropriate parameters for
the task you wish to use Linrad for. The default parameters are
there not as recommended settings but as something that allows
a starting point from where one can start experimenting.

I intend to place several more examples here:
http://www.sm5bsz.com/linuxdsp/usage/examples.htm

Unfortunately an upgrade of Debian Etch made it unstable, it crashes
when I try to run SDR-14 on it and I do not know how to recover.
After trying SDR-14 under the latest Debian Etch, boot becomes
impossible. I get the message /dev/hda1 does not exist:-(
I have not seen this problem before the latest upgrade or under 
any other operating system. I have a feeling that interrupt sharing
is the cause - but I really do not know.

Currently I can only install SDR-14 on a few systems. Header files
are missing or the USB is not properly supported. Red Hat 9 as an
example runs fine on my lap-top and on the Pentium II but on the
PentiumIV it can not find the SDR-14.

There are still many problems with SDR-14 under Linux:-( 
Presumably it works better under Windows where USB drive
routines should be more stable.


73

Leif

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