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

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

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. 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

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

Jay Salsburg wrote: Buy an OsmoSDR. //Peter