new TV Tuner Chip, the Si2177

Jürgen Kahrs juergen.kahrs at googlemail.com
Tue Sep 24 08:26:58 UTC 2013


Hello Leif,

>> How useful is such a "wide bandwidth" for users ?
> It allows efficient removal of strong static rain QRN.

This is an aspect that is completely new to me.
I was guessing more in the direction of recording hundreds
of channels simultaneously.

>
>> How many of them really need such a wide bandwidth ?
> On VHF bands I would say 80% or more, but only a during
> rain summertime, and only when the raindrops are charged.
>
> Have a look at the lower left corner of figure 1 here:
> http://www.sm5bsz.com/lir/recordings/static-rain.htm
>
> There you can see the sequence of pulses that originate from
> one raindrop hitting one of the elements of a yagi array.
> The sampling speed is 2 MHz and it is not quite enough.
> The pulses immediately after the first discharge are not 
> resolved.

That's funny. Charged raindrops causing pulses.
But it makes sense that a higher sampling rate can simply
removal of such disturbances. A sampling rate of 5 to 10 MHz
is easily implemented with the PCIe-9842. My first trials with my
own software used 5 and later 20 MHz. At the moment, my
recordings use 200 MHz by default. Thanks to the PCI express
interface and a good driver software, the transfer of 400 MB/s
puts no load onto the CPU. It is only the signal processing that
causes a high computational burden onto the hardware.

Up to now I have processed the data from the PCIe-9842 with
my own channelizer software. For example, in the medium wave
range of radio stations between 522 kHz and 1656 kHz there are
127 channels spaced in a 9 kHz raster. My software demodulates
all of them simultaneously (AM) and saves the data of all channels
into one .wav file. This .wav file can be processed later with the
Audacity sound editor, the only editor I know that can handle 127
channels with PCM data. The signal processing of the channelizer
runs on my graphics card (nvidia GTX 660TI with 1344 GPU cores).
I guess that the noise removal for the raindrops can also be done
on the graphics card, even with 200 MHz.

>
>> My device is an ADLINK digitizer PCIe-9842:
>>
>>   http://www.adlinktech.com/PD/photo/display/PCIe-9842/PCIe-9842_bimg_1.jpg
>>
>> This digitizer can sample at 200 MHz on a single input channel.
>> So this is very different from the other devices that are discussed
>> here: No antenna amplifier, no mixer, no AGC. At 200 MS/s it is
>> hard to emulate all the missing hardware parts in software.
>> Since there is no mixer, the software can demodulate only
>> frequencies in the range of public radio stations (short wave).
>> Would it make sense to have Linrad support such a device ?
>> Or is this device just too limited to be of interest ?
> Yes:-) I did not know about this card although it seems to come
> from a Swedish company. I will call them tomorrow:-)
>

ADLINK is a taiwanese company, as far as I know.
The Swedish company you mean is probably Strategic Test in Stockholm.
They offer excellent cards with Linux support, but too expensive for me.

I have downloaded the source code of Linrad and had a short look at it.
Why don't you put the source code into a Subversion repository at SourceForge ?
Storing the source code there costs nothing and simplifies access.
It looks like there is a systematic way of integrating new devices into
the Linrad source code. If I tried to integrate the PCIe-9842, would
you consider my source code for acceptance to  into Linrad ?




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