new TV Tuner Chip, the Si2177

Leif Asbrink leif at sm5bsz.com
Mon Sep 23 19:46:35 UTC 2013


Hi Jürgen,

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

> 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.

At a speed of 96 kHz the entire time period is a noise burst
that can only be removed by gating out the entire time span.
When the number of raindrops increases, 96 kHz does not work
because the noise bursts would overlap. I would think 5 MHz
would be about optimum (with todays computer hardware and
Linrad.) It would allow removal of S9+20 dB noise from static 
rain and give the normal noise floor with no adverse effect
on weak or strong signals.

With the very high bandwidth one might discover that there
is (removable) noise from charged dust whenever winds are 
high in dry weather. I do not know, but the static rain 
statement is based on solid experience with an equivalent 
wideband blanker (5 or 10 MHz wide) that I was using many
years ago:
http://www.sm5bsz.com/rtblnk/rt0669.htm

> Up to now it always looked like users were mostly interested in single channels.
> I am new to this list and don't know what others are doing.
> 
> The other reason I am asking is because I have got a very
> different device with a bandwidth of 100 MHz running and
> I wonder if I am the only one playing with such things.
> 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:-)

73

Leif / SM5BSZ




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