[linrad] 1: Questions and assumptions [by OH1ZAA - Chapter_1]

[Zaba <zaba@xxxxxx>]

1: Questions and assumptions [by OH1ZAA - Chapter_1]
(thread started June 14, 2004 with Chapter 'zero')

'Linrad' can be classified as a unique branch in the present 
developments of Software Defined Radio (SDR). It has several 
features that you will not easily find in any other SDR-branch. 

In my view the most important characteristic of 'Linrad' is its 
ability eliminate many forms of intermittent or persistent man-
made noise completely, especially the sort of noise coming from 
all kinds of spiky sources like brush engines, power-line leaks, 
welding arch's, faulty ignition and the like. This means that 
for 95% of potential weak signal operators the suffering has 
come to an end, and the impossible situation can be turned to 
a fruitful working environment that is virtually noiseless.

Since the spiky sort of industrial or man-made noise does not 
produce much of a power spectrum at microwave frequencies, my 
guess is, that the biggest benefit of 'Linrad'-techniques can 
be gained in the 25-300 MHz range when considering trade-offs 
with noise cancellation and dynamic range. However, due to all 
the other features, the technology is beneficial for general 
use at any given part of the spectrum. At the present stage 
of development everything seems to be optimized for weak CW 
reception, but much more is coming our way.

Given an operational mid-range PC with the appropriate SVGA- 
and audio cards, a top quality receiver can be obtained with 
less than 50 dollars/euros of home brew additions. For noise 
suppression that little setup will beat commercially available 
receivers in over 95% of circumstances, beating even the most 
expensive equipment costing 10k...50k units or more...  
 
After the tweaking of the noise suppression properties, dynamic 
range can be improved with increasing cost per additional decibel 
of improvement. However, if one is willing to operate the gain knob 
of the receiver just a bit more often, probably 99% of signals can 
be heard instantly with the 50 dollar circuits, compared with a 5000
dollar realization of 'Linrad'. The cost for extra dynamic range is 
quickly mounting to over 500 dollars/euros per dB, and the need 
for that is only in extreme situations with permanent changes 
for strong nearby signals. It does not mean that the more 
expensive setup would be any more sensitive, i.e. during 
absence of extreme signals elsewhere in the bandwidth, the 
whole spectrum would be equally observable, with a given 
equal sampling rate of the sound card in both situations. 

So far I have installed 'Linrad' software under SuSE 8.0 Linux 
with kernel 2.4.18, Knoppix 3.4 (kernel 2.4.26/2.6.5) and Gentoo 
Linux 2.4.25-r2 with OSS sound drivers in all cases, and svgalib
1.4.3 (1.9.17 under Gentoo). My biggest battles have been with 
the 1.9.19 svgalib_helper.o module, like reported by many others, 
and I have never succeeded to get it going. These days I am able 
to install and configure the full set of linrad 01-20 and svgalib 
1.4.3 software in an hour, but I spent 15 months to understand 
that in SuSE 8.0 the mouse has to be set right for both the SuSE 
main package and the libvga.config file. With almost 20 years of 
DOS/Windows experience a lot of energy has to be spent on learning 
the tricks and philosophy of Linux (surely a worthwhile activity).

Old SVGA cards like the i740-based Gigabyte (AGP), S3-based (PCI), 
ATI Radeon-7000 and Powercolor M64 cards work with svgalib 1.4.3, 
but Matrox G400MAX does not work. Gentoo is very coherent, and its 
"native" 1.9.17-r2 svgalib took the unknown SVGA-card
automatically.
Many modern SVGA_3D cards (like a Ti4200) operate flawlessy (VESA).
 
Gentoo is probably the best Linux-version for people that want to 
know all the nuts and bolts and backgrounds in the long run, and it 
can be updated (synchronized) on a daily basis (by Internet
sync's).  
  
Sound cards are under study, and there is a lot of confusion to sort
out, just to understand that e.g an AC'97 mixer indication does not 
mean that it has anything to do with a VIA AC97 OSS driver. For the 
newcomer it is initially a dark jungle out there, and it will take 
a lot of time just to find out how to disconnect the internal path 
of the analog input and output of a sound card with the
mixer(s)!!

So far I have only once been able to feed actual audio signals through
a functional 'Linrad' setup, and now I have realized that I should have
tried that much earlier. In Chapter_2 I will try to indicate some advice
for the newcomer, in order to achieve faster results with this system.

I must say that the first contact with the 'Linrad'-processed signals
was quite a shock in the positive sense (a long awaited
experience).     
A simple pulse generator will be soon available in order to be able 
to calibrate a simple and inexpensive front-end for the sound card.

Keep us informed of YOUR experiments! 
                     
                                         
73, "Zaba"  OH1ZAA


Initial Chapter_0 below ..... 
(future chapters will be stored in the archive)

http://www.antennspecialisten.com/linrad-archive/


Questions and assumptions [by OH1ZAA - Chapter_0]

'Linrad' is an extremely interesting development, and it is 
great to see many of the former VHF/UHF/SHF pioneers working 
with a new type of challenge/tool for weak signal reception.

There is much more behind the visible detail, and for the 
newcomer it is very hard to know where to begin. My guess 
is that Leif, SM5BSZ, is investing at least 14 hours a day 
into this development, and he has been doing that for many 
years now, possibly adding up to 30,000 hours. Also he is 
admirably commenting on the majority of the email passing 
through the 'Linrad'-list. 

This is my first time to post through the list. However, I 
have been communicating with Leif directly over the last two 
years, and I have done a couple of attempts to get 'Linrad' in 
action on several PC's. Initially it has mainly been a lesson 
in Linux, and between failures there have been long breaks...

During last weekend's RATS VHF/UHF/SHF-meeting in the OHo_Aland 
Islands it was good to see Leif's solid 'Linrad'-setup in full 
operation, and we did some thorough measurements on a FT-857D. 
So besides being the ultimate receiver for weak signals in very 
difficult environments, it is also an instrument to characterize 
the performance of commercial or homemade communications gear.

When reading through all the 'Linrad' documentation and related 
QEX-publications, one gets easily overwhelmed by the huge amount 
of information. However, I have noticed that I get to know more 
and more, and maybe soon I will know "too much" to be able to
ask 
the numerous questions that I have had before. Therefore I thought 
that it would be good to make maybe a dozen short email chapters 
with issues related to the interpretations of 'Linrad' features, 
and maybe a guided approach for the newcomer, who will be asking 
possibly the same sort of questions. This is chapter 'zero'; more 
of these will follow at random, but in correct numbering
sequence.

In the meantime I wish you all good luck with Linrad experiments.

                                      
73, "Zaba" OH1ZAA/2




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