6 Jul
2012
6 Jul
'12
9:52 a.m.
I am trying to implement equivalent time sampling using an EZCAP dongle configured using
gnuradio-companion. Since I am not completely clear about the tasks of the E4000 wrt
RTL2832,
it could be that I am missing a significant information, so here is my experimental setup
aimed
at developing a monostatic pulse mode RADAR :
* I am using a radiofrequency acoustic delay line to generate 4 echos delayed 1 to 2
microseconds
after an incoming excitation pulse is generated by a frequency synthesizer. The excitation
pulse
is 125 ns long, and repetition rate is 4 microseconds. The carrier frequency at 860 MHz is
chopped
by a fast duplexer, one side being connected to the frequency synthesizer and the other
sizer to the
EZCAP dongle
* the EZCAP is configured with an LO at 860 MHz, 2 MS/s output, and I plot |I+jQ| after
keeping
only 1 every 8 sample (2 MS/s=500 ns delay between samples, and 1 every 8 samples means a
spacing
of 4 us, close to the emitted pulse repetition rate)
* equivalent time sampling is obtained by slightly tuning the emitted pule repetition rate
off the
4 us: I have checked that I can indeed obtain time stretching by tuning the pulse
repetition rate
+/- 50 ns away from the 4 us dela, with time stretching factors of up to 10^5 (ie the 4 us
pulses
are recorded as 400 ms traces (thus including 10^5 points or an equivalent sampling rate
of 25 GS/s).
Now of course a stretching factor of 10^5 is overkill and the RF front end definitely does
not have such
a huge bandwidth, this is just to demonstrate the concept. With a more reasonable
stretching factor of 10 (ie
sampling every 4.4 us with a 4 us emission pulse repetition rate), I can expect to convert
a 2 MS/s sampling rate
to an equivalent time sampling of 20 MS/s, which would already improve my monostatic RADAR
resolution by a factor 10,
and more or less fit my targetted resolution.
So now the questions:
* the 125 ns pulse I generate would span 8 MHz. From my reading of the E4k description,
this is within the
IF bandwidth available. However, although I can observe the emitted pulse (0 dBm), I
cannot see the echos
(-35 to -40 dBm), whatever LNA gain I use (from 0 to 40 dB). Is the default configuration
of the E4k an IF of
8 MHz, or lower. What parameter should I give the rtlsdr gnuradio source block to make
sure I have the right bandwidth ?
* since I am not clear about task distribution between the E4k and the RTL2832, is there
another limitation that
will prevent a 8 MHz wide (bandwidth) signal to be recorded through the 2 MS/s I/Q output
recorded ?
Thank you, Jean-Michel
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 32 av. observatoire, 25044 Besancon,
France
6 Jul
6 Jul
10:19 a.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
The rtl-sdr (and all other software) has only a bandwidth of 3.2MHz
maximum available. Only the hardware demodulator inside the realtek chip
can process full 8MHz. If you consider the filter setting of the rtl-sdr
you effective bandwidth is about 2 MHz. It is hard coded in the tuner
code but reasonable for most settings, as it avoids aliasing.
Am 06.07.2012 09:52, schrieb friedtj:
I am trying to implement equivalent time sampling
using an EZCAP dongle configured using
gnuradio-companion. Since I am not completely clear about the tasks of the E4000 wrt
RTL2832,
it could be that I am missing a significant information, so here is my experimental setup
aimed
at developing a monostatic pulse mode RADAR :
* I am using a radiofrequency acoustic delay line to generate 4 echos delayed 1 to 2
microseconds
after an incoming excitation pulse is generated by a frequency synthesizer. The
excitation pulse
is 125 ns long, and repetition rate is 4 microseconds. The carrier frequency at 860 MHz
is chopped
by a fast duplexer, one side being connected to the frequency synthesizer and the other
sizer to the
EZCAP dongle
* the EZCAP is configured with an LO at 860 MHz, 2 MS/s output, and I plot |I+jQ| after
keeping
only 1 every 8 sample (2 MS/s=500 ns delay between samples, and 1 every 8 samples means a
spacing
of 4 us, close to the emitted pulse repetition rate)
* equivalent time sampling is obtained by slightly tuning the emitted pule repetition
rate off the
4 us: I have checked that I can indeed obtain time stretching by tuning the pulse
repetition rate
+/- 50 ns away from the 4 us dela, with time stretching factors of up to 10^5 (ie the 4
us pulses
are recorded as 400 ms traces (thus including 10^5 points or an equivalent sampling rate
of 25 GS/s).
Now of course a stretching factor of 10^5 is overkill and the RF front end definitely
does not have such
a huge bandwidth, this is just to demonstrate the concept. With a more reasonable
stretching factor of 10 (ie
sampling every 4.4 us with a 4 us emission pulse repetition rate), I can expect to
convert a 2 MS/s sampling rate
to an equivalent time sampling of 20 MS/s, which would already improve my monostatic
RADAR resolution by a factor 10,
and more or less fit my targetted resolution.
So now the questions:
* the 125 ns pulse I generate would span 8 MHz. From my reading of the E4k description,
this is within the
IF bandwidth available. However, although I can observe the emitted pulse (0 dBm), I
cannot see the echos
(-35 to -40 dBm), whatever LNA gain I use (from 0 to 40 dB). Is the default configuration
of the E4k an IF of
8 MHz, or lower. What parameter should I give the rtlsdr gnuradio source block to make
sure I have the right bandwidth ?
* since I am not clear about task distribution between the E4k and the RTL2832, is there
another limitation that
will prevent a 8 MHz wide (bandwidth) signal to be recorded through the 2 MS/s I/Q output
recorded ?
The e4k does the filtering but has an analog output. The RTL2832 is in
effect an USB ADC.
7 Jul
7 Jul
12:21 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
The e4k does the filtering but has an analog output.
The RTL2832 is in
effect an USB ADC.
apologies if this is obvious to everyone and has already been posted (I have not checked
the whole history of this ml), but indeed by connecting a couple of wires to the I or Q
differential
inputs of the RTL2832 you do get a fine 2 MS/s oscilloscope. This unfortunate AGC means
that
DC signals cannot be monitored (even after soldering the wires after the common mode
cutoff capacitors),
but neverless this does provide a 40 fold sampling rate improvement with respect to the
use of sound
cards as A/D converters (http://sequanux.org/jmfriedt/199999720input_middle.png and
http://sequanux.org/jmfriedt/199999720input_top.png for the I and Q measurements when an
input signal of
199.999720 kHz is generated by a synthesizer in order to synchronize with the sampled
data, ie the
sampling clock is off by 1.4 ppm, not too bad !).
JM
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 32 av. observatoire, 25044 Besancon,
France
4:08 a.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
Can I say I am impressed with what you are doing friedtj. One thing I have
wanted to do with these new Dongles with the e4000 tuners is bypass the
RTL2832 chip and piggyback a better ADC on the e4000 tuners output. Since
there is so much activity in the "Group" of squeezing the maximum
performance from the Dongle Tuners, it may be time to add better hardware.
Just to test to see if this is a good route to take, it should be possible
to connect a decent PC audio card to the output of the e4000 tuner to see if
it suffers any degradation, the AGC debacle can also be checked with this
method. If no problems arise then addition of a dual input, 14 bit, 100
Mega-sample, ADC would be the next step to take full advantage of the
bandwidth and dynamic range of the tuner that the RTL2832 chip is obviously
and purposefully limiting; forget the RTL2832 chip. Will someone publish the
e4000 tuner's datasheet and stop all the IP BS.
-----Original Message-----
From: osmocom-sdr-bounces(a)lists.osmocom.org
[mailto:osmocom-sdr-bounces@lists.osmocom.org] On Behalf Of friedtj
Sent: Friday, July 06, 2012 2:53 AM
To: osmocom-sdr(a)lists.osmocom.org
Subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle
?
I am trying to implement equivalent time sampling using an EZCAP dongle
configured using gnuradio-companion. Since I am not completely clear about
the tasks of the E4000 wrt RTL2832, it could be that I am missing a
significant information, so here is my experimental setup aimed at
developing a monostatic pulse mode RADAR :
* I am using a radiofrequency acoustic delay line to generate 4 echos
delayed 1 to 2 microseconds after an incoming excitation pulse is generated
by a frequency synthesizer. The excitation pulse is 125 ns long, and
repetition rate is 4 microseconds. The carrier frequency at 860 MHz is
chopped by a fast duplexer, one side being connected to the frequency
synthesizer and the other sizer to the EZCAP dongle
* the EZCAP is configured with an LO at 860 MHz, 2 MS/s output, and I plot
|I+jQ| after keeping only 1 every 8 sample (2 MS/s=500 ns delay between
samples, and 1 every 8 samples means a spacing of 4 us, close to the emitted
pulse repetition rate)
* equivalent time sampling is obtained by slightly tuning the emitted pule
repetition rate off the
4 us: I have checked that I can indeed obtain time stretching by tuning the
pulse repetition rate
+/- 50 ns away from the 4 us dela, with time stretching factors of up to
+10^5 (ie the 4 us pulses
are recorded as 400 ms traces (thus including 10^5 points or an equivalent
sampling rate of 25 GS/s).
Now of course a stretching factor of 10^5 is overkill and the RF front end
definitely does not have such a huge bandwidth, this is just to demonstrate
the concept. With a more reasonable stretching factor of 10 (ie sampling
every 4.4 us with a 4 us emission pulse repetition rate), I can expect to
convert a 2 MS/s sampling rate to an equivalent time sampling of 20 MS/s,
which would already improve my monostatic RADAR resolution by a factor 10,
and more or less fit my targetted resolution.
So now the questions:
* the 125 ns pulse I generate would span 8 MHz. From my reading of the E4k
description, this is within the IF bandwidth available. However, although I
can observe the emitted pulse (0 dBm), I cannot see the echos
(-35 to -40 dBm), whatever LNA gain I use (from 0 to 40 dB). Is the default
configuration of the E4k an IF of
8 MHz, or lower. What parameter should I give the rtlsdr gnuradio source
block to make sure I have the right bandwidth ?
* since I am not clear about task distribution between the E4k and the
RTL2832, is there another limitation that will prevent a 8 MHz wide
(bandwidth) signal to be recorded through the 2 MS/s I/Q output recorded ?
Thank you, Jean-Michel
--
JM Friedt, FEMTO-ST Time & Frequency/SENSeOR, 32 av. observatoire, 25044
Besancon, France
10:34 a.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
If no problems arise then addition of a dual input, 14
bit, 100
Mega-sample, ADC would be the next step to take full advantage of the
bandwidth and dynamic range of the tuner that the RTL2832 chip is obviously
and purposefully limiting;
1) AFAIK, The E4000 has a limited output bandwidth, in the range of 8
MHz max usable IIRC. It's designed for DVB/TV applications and they
don't need more so the IF filters available don't go above that.
2) You still need to pipe all those samples to the PC somehow, this
will raises the price of all of this way above the original 20 USD and
make it a much bulkier setup.
Cheers,
Sylvain
8 Jul
8 Jul
4:52 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
If all you want to do is watch and listen to HAM and Police Trunk Radio, the $20 Dongle is
adequate, but if you want to hack the E4000 Tuner, a better ADC is needed.
1) Yes, if all you need is to be able to detect a signal on an analog stream its Nyquist
Frequency will do, (2 times the frequency being measured) a 20 megasample ADC would be
adequate for the E4000 tuner's I/Q output, but there is more information in the Stream
than just the presence of Radio Frequency Energy. If all you need to do is detect the
presence of energy or listen to it (Audio Modulation) a 2 times Sample frequency is
adequate, but if you need to decode octal phase modulated sideband signals, you need to go
to at least 10 times Analog to Digital. This is the case with many signals on Satellite
and Cable Streams and it is the case with many phase modulated signals over the air.
Instead of just the minimum Conversion being done, you need 10 times the Conversion to
reconstruct the modulation, and this may even miss subtle information. It is information
we are seeking, information as intelligence modulating Electromagnetic Energy. Cable
Modems, for example, Digitize the entire spectrum from 100,000 KHz to 800 MHz. This is
because the TV Signals are encrypted with Octal Phase Modulation. You have to be able to
digitize with wideband (multi-Hundred Megahertz Converters) to be able to Analyze, Decode,
or even just to detect these modulation schemes. So even though the E4000 Tuner has only 8
MHz Bandwidth. You need at least 10 times that bandwidth to accurately reconstruct Phase
Modulated Signals. In the vernacular of ADCs, anti-aliasing filters are required to remove
unwanted high frequency content. Thus content is discarded, and noise is introduced. To
adequately sample a broadband signal without discarding anything, radical oversampling is
required. Oversampling allows Signal Processing to take place like Noise Reduction, with
is very important for DXing. ADCs are cheaper than ever, driven by Scientific
Instrumentation, Satellite, and Cable Industry needs.
2) Remember back a in the 1990s when USB first came to be. It was expensive and a luxury
on high end computers. Now we have things like the Tuner Dongle with USB and virtually
every computer with USB as a Standard; now there is USB 3; even faster. Apple came up with
FireWire to solve the problem that USB had. FireWire is capable of real-time wideband
serial communication. Better yet, even though it is still expensive, ThunderBolt will
become the new "USB." At Multi-Gigabit Streaming rates (800 Mega Bytes per
second). You will see in the near future, ADCs with USB 3 and ThunberBold built-in. There
is just too much money to make. Current High Definition Cameras use SDI to stream their
signals. There are already available Video equipment servicing the High Definition
Television Industry with both SDI and ThunberBolt Side-by-Side. You may pooh-pooh this as
too expensive, but so was USB when it first rolled onto the scene.
-----Original Message-----
From: Sylvain Munaut [mailto:246tnt@gmail.com]
Sent: Saturday, July 07, 2012 3:34 AM
To: Jay Salsburg
Cc: osmocom-sdr(a)lists.osmocom.org
Subject: Re: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
If no problems arise then addition of a dual input, 14
bit, 100
Mega-sample, ADC would be the next step to take full advantage of the
bandwidth and dynamic range of the tuner that the RTL2832 chip is
obviously and purposefully limiting;
1) AFAIK, The E4000 has a limited output bandwidth, in the range of 8 MHz max usable IIRC.
It's designed for DVB/TV applications and they don't need more so the IF filters
available don't go above that.
2) You still need to pipe all those samples to the PC somehow, this will raises the price
of all of this way above the original 20 USD and make it a much bulkier setup.
Cheers,
Sylvain
5:29 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
1) Yes, if all you need is to be able to detect a
signal on an analog stream its Nyquist Frequency will do, (2 times the frequency being
measured) a 20 megasample ADC would be adequate for the E4000 tuner's I/Q output.
This is IQ signal you don't need twice the bandwidth, you only need
once. So a 8 Msps IQ would be adequate to represent a 8 MHz bandwidth.
[snip ....]
You need at least 10 times that bandwidth to accurately reconstruct Phase Modulated
Signals.
No you don't. You want a concrete example: Most GSM phone are
demodulating a phase modulated signal by sampling at exactly one
sample per symbol (so they're even sampling _lower_ than the actual
signal bandwidth)
And although oversampling is useful in certain case to analyze signal,
it's essentially useless if the signal has _already_ been filtered
like it is in the E4000 case. If the IQ output has only 8 MHz of
useful content at the output, you can oversample all you want, it
won't bring back what the E4000 discarded ... Those antialiasing
filter you mention, they're in the E4000 !
2) I didn't say bigger / better SDR would be useless ... I'm just
saying if you're spending hundreds / thousands on better ADC and
better PC interface you might as well ditch the E4000 and use a better
RF front end as well. The spectral output of the E4000 is far from
being "clean", there is distortions / LO leakage / random spurs /
28.8M clock leakage / ... etc ... Oh and Elonics declared bankrupcy so
the E4000 supply is fading ...
Cheers,
Sylvain
7:30 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
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. The Tuner Dongle offers a low cost opportunity for an enterprising hacker to jump
ahead and produce a product worth pursuing. As is it is very limited.
Also, GSM is very narrowband voice. Data is wideband and complex, Data is where the Gold
is, mining it takes better tools which the RTL2832 prevents application to the reception.
Typical low price ADC ...The ADC12DS105 is a dual 12-Bit, 105 Msps A/D Converter
http://www.ti.com/product/adc12ds105 Price $31
http://www.ti.com/tool/adc12ds105lfeb Design Kit $495, Accessories include a USB
Interface
http://www.ti.com/solution/software-defined-radio-sdr-diagram
http://www.ti.com/lit/an/slaa407/slaa407.pdf
How to Select the (Best Minimum) Sampling Rate
The selection of sampling rate is also important for ADCs. Fast encode clocks offer the
advantage of
making analog filtering significantly easier. Given a fixed signal bandwidth, a higher
encode rate increases
the allowable transition band. This allows lower order filters to be used to reduce cost,
or, if higher order
filters are still used, greater stop band rejection can potentially be realized.
Another advantage with increasing clock speeds is processing gain. Processing gain is
achieved when the
signal of interest is oversampled and then digitally filtered. Processing gain occurs when
noise outside the
band of interest is digitally removed, which results in improved in-band SNR. Processing
gain can be
easily determined using Equation 1. This equation determines the increase in SNR over and
above the
SNR of the converter alone.
Processing Gain = 10log10 (Half of the sample rate/ filter BW)
Also, when selecting the sampling rate, the user must consider the second and third
harmonics (HD2 and
HD3). These harmonics must lie outside the band of interest. These can be filtered using
the digital filter
inside the DDC/DSP. That means, frequency planning also becomes important when designing a
SDR
system.
-----Original Message-----
From: osmocom-sdr-bounces(a)lists.osmocom.org [mailto:osmocom-sdr-bounces@lists.osmocom.org]
On Behalf Of Sylvain Munaut
Sent: Sunday, July 08, 2012 10:29 AM
Cc: osmocom-sdr(a)lists.osmocom.org
Subject: Re: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
1) Yes, if all you need is to be able to detect a
signal on an analog stream its Nyquist Frequency will do, (2 times the frequency being
measured) a 20 megasample ADC would be adequate for the E4000 tuner's I/Q output.
This is IQ signal you don't need twice the bandwidth, you only need once. So a 8 Msps
IQ would be adequate to represent a 8 MHz bandwidth.
[snip ....]
You need at least 10 times that bandwidth to accurately reconstruct Phase Modulated
Signals.
No you don't. You want a concrete example: Most GSM phone are demodulating a phase
modulated signal by sampling at exactly one sample per symbol (so they're even
sampling _lower_ than the actual signal bandwidth)
And although oversampling is useful in certain case to analyze signal, it's
essentially useless if the signal has _already_ been filtered like it is in the E4000
case. If the IQ output has only 8 MHz of useful content at the output, you can oversample
all you want, it won't bring back what the E4000 discarded ... Those antialiasing
filter you mention, they're in the E4000 !
2) I didn't say bigger / better SDR would be useless ... I'm just saying if
you're spending hundreds / thousands on better ADC and better PC interface you might
as well ditch the E4000 and use a better RF front end as well. The spectral output of the
E4000 is far from being "clean", there is distortions / LO leakage / random
spurs / 28.8M clock leakage / ... etc ... Oh and Elonics declared bankrupcy so the E4000
supply is fading ...
Cheers,
Sylvain
9:29 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
On Sun, 8 Jul 2012 12:30:05 -0500
"Jay Salsburg" <jsalsburg(a)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
9 Jul
9 Jul
5:21 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
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(a)lists.osmocom.org
[mailto:osmocom-sdr-bounces@lists.osmocom.org] On Behalf Of Leif Asbrink
Sent: Sunday, July 08, 2012 2:29 PM
To: osmocom-sdr(a)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(a)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
11:26 p.m.
New subject: stroboscopic (aka equivalent time sampling) using EZCAP DVB dongle ?
Hello Jay,
Well, this is interesting. Think out of the box. Ask
yourself if a 8 bit NFM
is high fidelity.
You have to specify what you mean by this.
The NFM signal carries information by the instantaneous frequeny
of the signal. When sampled with 8 bit frequently enough the
frequency can be determined with great precision.
I do high fidelity; 6 channel, 24 bit Wav files, that
is
high fidelity.
This statement is basically false. There is no way that you could
have
24 bit accuracy in a .wav file (unless the waveforms are synthetized
in the computer from mathematical functions.)
A good 24 bit soundcard like the Delta 44 provides 18 bit data.
Bits 19 to 24 contain only noise and can be truncated without
any effect on the recorded information. The best modern A/D
converters may provide nearly 20 bits, but providing 24 bit is
not possible. The noise floor is set by the thermal noise
of any resistor at room temperature.
The 8 bit data in RTL2832 is from two separate A/D converters
and together they provide 8 bit at 4MHz sampling rate. That is
the same as 9 bit at 1MHz or 10 bit at 250 kHz or 11 bit at 62.5 kHz.
I was thinking you were referring to FM broadcast in which case
the FM detector would improve S/N by about 20 dB. (3 bit)
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).
Hmmm, "Audio NFM"? do you
mean the audio signal delivered by an FM detector?
They would have about 13 bit accuracy when produced from the 8 bit 2*2 MHz
data stream from a rtl2832. In real life the S/N would limit performance
and it would be identical to what you observe on a better radio unless you
have really strong interferring signals.
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.
It does not
matter at all whether we do anti-aliasing in analog hardware
or whether we sample at a higher rate and do it by a digital filter.
The result is identical.
The effective bandwidth is what matters.
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.
Well, I did that and came to the
conclusion it would be a good idea
until the AGC problem was solved. Now, without the AGC, the RTL2832
chip matches the performance of the E4000 tuner pretty well.
Adding a much better A/D converter will not improve performance
significantly. We would need a better tuner to motivate a better
A/D converter.
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.
Are you sure you know what
you are saying here?
The RTL2832/E4000 dongle provides a dynamic range of 80 dB.
You might tell us what the received power levels are from
the stations you want to hear - and what is the signal level
of the stations that might interfere (high power squawking
Police channels...)
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.
The
RTL2832 is just a dual A/D converter. (As operated for SDR)
Replacing it with something 2 or 3 times faster would allow
us to remove the alias signals that we see in the DVB dongles.
It would not improve performance much in other respects however
because the minimum noise floor from the E4000 is about 1 bit
on the RTL2832 and running the E4000 at higher output levels
would make the harmonic distortion unacceptable.
Surely performance of the DVB dongle is limited, but it is not
bad. Quite respectable actually. (But you need the latest
software - or maybe even a little later than what you can
download today. I have not evaluated the latest changes so
I do not know.)
Regards
Leif / SM5BSZ
4319
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11 comments
6 participants
participants (6)
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friedtj -
Jay Salsburg -
Leif Asbrink -
Peter Stuge -
Stefan Sydow -
Sylvain Munaut