[linrad] Re: Linrad-02.39

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

Hi Joe,

> The links to the data files (blinkerinitx.xxx) are broken (but I found them 
> anyway :-)).
Thanks for telling me. I have corrected the links (hopefully)

> One small issue, in windows, adfile is selected instead of adfile.txt 
> (assuming both are present).
Yes. I do not remember why i made it that way, but there must have been
some reason.......

Linrad always looks for adfile first, then adfile.txt if adfile was not
present. For some unknown reason the Linux adfile seems to
work under Windows.....

> I have not tried the transmit function, but have noticed no problems in 
> other functions so far.
Good:-)
The transmit side is not complete, and I do not think I will have the
hardware to test it this year......

> I'll try and find some files for you to work on.  I'm pretty sure various 
> low banders have samples out on the web of signals fading in and out of the 
> noise (complete with static crashes, powerline noise, electric fences, 
> plasma TV buzz, ethernet birdies, etc.).  I'll make a recording of my 144 
> MHz environment that will be a real challenge!
The problem (to me) is that low banders record their data on un-calibrated 
systems and that may cause the problem to look more difficult than it 
really is....

> Another one of my interests is low band (160/80 meters) where my noise level 
> is very high.  I have been thinking about installing a 4 square receive 
> antenna system similar to the DX Engineering system ( 
> http://www.dxengineering.com/ ) or perhaps the 2 antenna version with the 
> NCC-1 noise cancelling unit.  It seems to me that the primary functions of 
> these units (controlling the position of the main lobe of the 4 square 
> and/or noise cancelling) would be better accomplished in DSP (certainly 
> cheaper).  I was thinking about using four 160/80 meter softrocks (one for 
> each antenna with common sampling clock) and feeding the I/Q output of each 
> softrock into one channel of a D44 sampling at 96KHz.  That (I think) would 
> result in ~48 KHz sampled bandwidth (which may not be wide enough for very 
> effective noise blanking) and the softrocks probably aren't the best 
> frontends, but it would be a very interesting (cheap) experiment.  Are these 
> functions (antenna beam forming and noise cancelling) something Linrad could 
> accommodate?  :-
With four softrocks you would need 8 analog inputs so a Delta44 would be
inadequate. There is the Delta 8?, an 8-channel version.
The hardware we should look for is something using a good VHF-sampling
A/D like the LTC

Linrad is currently limited to two channels. In principle it could be
adopted to any number of RF channels that you want to supply.
At the moment Linrad only optimizes for maximum signal when Linrad
is to adjust the polarization parameters. In a multi-antenna
situation it would be better to optimize for optimum S/N. Surely
possible, but I do not have the hardware to play with such things.

What we should look for is digital hardware with LTC2207 or similar
to sample at VHF (with proper randomization.)
We also need something to put into a PC to receive and down-convert 
tha data from any number of such units. Technically this should be
quite straight-forward, but I do not have the skils to do this 
developement.

To start with, you might use a Delta 44 and two softrocks with the
current Linrad software. You may use the manual polarization setting to 
cancel undesired signals, but you could also allow Linrad to optimize 
the signal level for the interference while you listen in the orthogonal
channel where the interference would be minimized.

Maybe you will be able to produce "interesting" files.....

73

Leif / SM5BSZ


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