stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?

Jay Salsburg jsalsburg at bellsouth.net
Mon Jul 9 15:21:13 UTC 2012


Well, this is interesting. Think out of the box. Ask yourself if a 8 bit NFM
is high fidelity. I do high fidelity; 6 channel, 24 bit Wav files, that is
high fidelity. When you have high conversion rates and high bit depth
signals you get high fidelity. Audio NFM signals are only meant to satisfy
walky-talky radio communication (Trunk Radio). The high value targets in
Radio technology today is Data Services. Look in the (Data Stream) Mine for
the Gold, Data is Gold. Data is wideband, multiple channel, and frequency
diverse (not NFM), then there are all those wideband RADAR Signals. With
high fidelity conversion you do not need anti-aliasing. Anti-Aliasing is a
technique to filter, the very word means to take something away. Data
services count on the fact that the Data is difficult to intercept.

The object of any great effort is to rise above all the rest. To get the
most out of the Tuner the ADC must be improved. All you guys have so much to
offer and you have spent so much of your time and money to get the most out
of this $20 Dongle, all because the Manufacturer refuses to open Source the
Chip. Jump ahead and make better use of it. Go to the next level and hack
the circuit, not just the Operating Code. 

The most extensive effort should be in acquiring intelligence from the
Either, not listening to high power squawking Police channels. This requires
very high granularity, the RTL2832 is low granularity. If you want to drop
in on intelligence from over the horizon, very good selectivity is required
and the RTL2832 is just not that; highly selective, intentionally by design.

-----Original Message-----
From: osmocom-sdr-bounces at lists.osmocom.org
[mailto:osmocom-sdr-bounces at lists.osmocom.org] On Behalf Of Leif Asbrink
Sent: Sunday, July 08, 2012 2:29 PM
To: osmocom-sdr at lists.osmocom.org
Subject: Re: stroboscopic (aka equivalent time sampling) using EZCAP DVB
dongle ?

On Sun, 8 Jul 2012 12:30:05 -0500
"Jay Salsburg" <jsalsburg at bellsouth.net> wrote:

> The E4000 Tuner offers a stepping stone into the world of SDRs. 
> It does the heavy lifting, significantly reducing the size, cost, and 
> complexity of a SDR. It does not do any programmable signal 
> processing, which is where SDRs are strongest.
> Quantization has been left out of the discussion because the
> RTL2832 is so bad at it (to conserve size and cost). The RTL2832 
> hamstrings the usefulness of the E4000 significantly narrowing the 
> application of DSP. If you want high fidelity reception, you must 
> apply a high fidelity ADC.

I do not understand how you think to arrive at this conclusion. 
The RTL2832/E4000 dongels allow superior quality demodulation of FM signals.

The suppression of neighbouring channels is limited due to aliasing, but it
is not bad and interference can be avoided by changing the LO frequency.
There is also a mirror image but if you use Linrad you can apply the
calibration procedure that eliminates image spurs.

Now that AGC is eliminated these dongles allow a pretty good general purpose
SDR at small cost.
http://www.sm5bsz.com/linuxdsp/hware/rtlsdr/rtlsdr.htm

The high fidelity reception is in no way limited by the ADC in these dongles
as long as the desired signal is not much weaker than surrounding signals.
(Much means 50 dB or so.)

Regards

Leif / SM5BSZ





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