new TV Tuner Chip, the Si2177

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Jay Salsburg jsalsburg at bellsouth.net
Sat Sep 21 22:34:57 UTC 2013


What is all this talk about USB. High-end Audio Interfaces digitize/quantize
at 192KHz/24bit. Since these new Tuners are almost naked on a surface mount
board, all that is needed other than a good audio card is a BusPirate to
control the I2C to get one of these new Analog TV tuner Chips to work as a
SDR. Since most "Intelligence" in radio is narrow band typically a Voice
Channel, all that a wideband A/D gives you is a view from 50,000 feet of the
spectrum which is OK for Test and Measurement. I cannot use my TV Dongles
for most of my (Forward Scatter RADAR) applications because of their low
resolution, I must use a conventional Scanner because it converts the signal
to Audio. What I need is high definition and narrow band, the current
Dongles are typically Wide Band low resolution (2Mhz/8bit). This is why a
Tuner Chip with low noise and demodulated analog output is attractive to me,
it is a complete solution.

-----Original Message-----
From: osmocom-sdr-bounces at lists.osmocom.org
[mailto:osmocom-sdr-bounces at lists.osmocom.org] On Behalf Of Leif Asbrink
Sent: Saturday, September 21, 2013 4:38 PM
To: osmocom-sdr at lists.osmocom.org
Subject: Re: new TV Tuner Chip, the Si2177

Hi Adam,

> > > The bandwidth of the I/Q pair is too large to be transmitted over 
> > > USB for the reception of TV signals. After demodulation the 
> > > bandwidth is lower so it would (marginally) fit an USB interface 
> > > if we talk about traditional analogue TV. For digital TV the 
> > > bandwidth reduction by the decoder is much larger.
> 
> Is that correct?  From what I can find, an analogue TV signal has a 
> bandwidth of around 6-8MHz.
Yes.

> The HackRF is an SDR that works over
> USB2.0 and can capture a chunk of RF spectrum up to 20MHz, which 
> should be ample for one analogue (or even digital) TV signal, perhaps 
> even two if the channels are close enough together.

I was under the impression that the USB channel was the reason that the
highest sampling rate I was aware of in continous mode is 4 MHz
(QS1R) Now, I did not think of the fact that for the dongle we need only 8
bit while normal SDRs use 16 bit so with my assumption the maximum sampling
speed would be 8 MHz. To receive 6-8 MHz bandwidth one would need to sample
quite a bit higher. Surely one could apply digital filters but even so a,
substantial amount of oversampling is needed.

Are you sure HackRF really can send 20 MHz of bandwidth over USB 2.0
continously? Where did you find that info? (Seems I should try to push SDR
manufacturers who use USB 2.0 to supply modes with higher sampling rates...)

73

Leif

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