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RTL-SDR and GNU Radio with Realtek RTL2832U [Elonics E4000/Raphael Micro R820T] software defined radio receiver.


Originally meant for television reception it was discovered by V4L/DVB kernel developer Antti Palosaari that these devices can output unsigned 8bit I/Q samples at ~2.8 MS/s. A phased locked loop based synthesizer produces the local oscillator required by the quadrature mixer. The quadrature mixer produces a complex-baseband output where the signal spans from -bandwidth/2 to +bandwidth/2 and bandwidth is the analog bandwidth of the mixer output stages. This is complex-sampled (I and Q) by the ADC. Then the ADC samples at 28.8Msps, and the results are resampled inside the RTL2832U to present whatever sample rate is desired to the host PC. This can be 3.2 MS/s but 2.4 MS/s is the max recommended to avoid losing samples. The actual output is interleaved; so one byte I, then one byte Q with no header or metadata (timestamps). The samples themselves are unsigned and you subtract 127 from them to get their actual {-127,+127} value.

The dongles with an E4000 tuner can range between 54-2200 MHz (in my experience) with a gap over 1100-1250 MHz in general. The R820T's go from 24-1700 Mhz. The tuner error is ~30 +-20 PPM, relatively stable once warmed up, and stable from day to day for a given dongle. The dynamic range for most dongles is around 45 dB. For the data transfer mode USB 2 is required, 1.1 won't work.

For the best information stop reading this page right now and go to the rtl-sdr wiki - OsmoSDR by the Osmocom people who created,

Do not use the dvb drivers on the CD or your OS. Those are for the dvb mode and not the debug mode that outputs raw samples. Linux 3.x kernel should check with "$ lsmod dvb_usb_rtl28xxu" and if found at least "$ sudo modprobe -r dvb_usb_rtl28xxu" to unload it.

SDR# is probably the best application to start out with but you'll have to compile from svn for linux+mono because of some non-portable mono ifdef's during building. Alternately, try gqrx for OSX (precompiled) or linux. multimode is good for linux if you have GNU Radio. For low cpu power and low ram devices try rtl_fm. On that note stevem provides rtlsdr and related tools for openwrt.

This page is mostly just notes to myself on how to use rtlsdr's core applications, 3rd party stuff using librtlsdr and wrappers for it, and lots on using the gr-osmosdr source in GNU Radio and GNU Radio Companion, Freenode's ##rtlsdr and reddit.com/r/rtlsdr were particularly helpful in getting the software running.


I bought two E4000 based rtlsdr usb dongles for $20 each in early 2012. Then many months later I bought two more R820T tuner based dongles for ~$11 each. Of the E4Ks the Newsky TV28T (yellow) was from ebay and arrived within two weeks, well before the DealExtreme dongle arrived. The (green) ezcap EzTV668 was from DealExtreme, payed for on March 25th (2012) and delivered on May 20th. There's a photo of an R820T tuner based dongle in the "mini" format off to the left. It and the Newsky dongle are MCX. Some of the cheaper dongles occasionally miss protection diodes but the last three I've bought have been fine. The antenna connector on the ezcap is IEC-169-2, Belling-Lee. I use a PAL Male to F-Connector Female with it and F to MCX for everything else.

Tuners

Only two tuners are very desirable at this time. The Elonics E4000 and the Raphael Micro R820T. In general they are of equal performance but the sticks with R820T chips are much easier to find and cheaper ($10 USD). The E4K is better for high end (>1.5Ghz+) while the R820T can tune down to 24 Mhz without any mods.

All of the dongles have significant frequency offsets from reality that can be measured and corrected at runtime. My ezcap with E4000 tuner has a frequency offset of about ~44 Khz or ~57 PPM from reality as determined by checking against a local 751 Mhz LTE cell using LTE Cell Scanner. Here's a plot of frequency offsets in PPM over a week. The major component of variation in time is ambient temperature. With the R820T tuner dongle after correctly for I have has a ~ -17 Khz offset at GSM frequencies or -35 ppm absolute after applying a 50 ppm initial error correction. When using kalibrate if the initial frequency error too large the FCCH peak might be outside the bandwidth. This would require passing an initial ppm error parameter (from LTE scanner) -e . Another tool for checking frequency corrections is keenerd's version of rtl_test which uses (I think) ntp and system clock to estimate it rather than cell phone basestation broadcasts.

2012-08-22: The E4000 tuner datasheet has been released into the wild. Elonics-E4000-Low-Power-CMOS-Multi-Band-Tunner-Datasheet.pdf, but...

"All the ones that are documented in the DS are 'explained'in the driver header file ... And the rest, the datasheet call them "Ctrl2: Write 0x20 there" and no more details"

2012-09-07: Experimental support for dongles with the Rafael Micro R820T tuner that started appearing in May has been added to rtl-sdr source base by stevem. These tuners cover 24 MHz to 1766 MHz. They also don't have the DC spike caused by the I/Q imbalance since they use a different, non-zero, IF. On the other hand, they might have image aliasing due to being superheterodine receivers. See stevem's tuner comparisons. On 2012-09-20 the R820T datasheet was leaked to the ultra-cheap-sdr mailing list. The official range is 42-1002 Mhz with a 3.5 dB noise figure. On 2012-10-04 my order arrived. I'm liking this tuner very much since it actually works well, locking down to 24 Mhz or so *without* direct sampling mode. Here's a rough gnuplot spectral map of 24 to 1700 Mhz over 3 days I made with some custom perl and python scripts. Don't judge the r820t on the quality of that graph, it is just to show the range. You can see where the front-end gets massively overloaded by pager transmissions which then appear broadly stretched over the high frequencies. I do almost no processing of the signal (ie, no IQ correction), don't clear the buffer between samples (LSB probably bad), and use a hacky way to display timeseries data in gluplot. Real SDR software like SDR# shows them to be equal in quality to E4ks.

stevem did gain measurement tests with a few dongles using some equipment he had to transmit a GSM FCCH peak, "which is a pure tone." This includes the E4000 and R820T tuners. In addition he measured the mixer, IF and LNA for the R820T.

High Frequency (0-30Mhz) Direct Sampling Mod

Steve Markgraf of Osmocom has created an experimental software and hardware modification to receive 0~30Mhz(*) by using the 28.8 MHz RTL2832U ADCs for RF sampling and aliasing to do the conversion. In practice you only get DC-14.4MHz in the first Nyquist zone but the upper could be had by using a 14.4 MHz to 28.8 MHz bandpass filter. In the stereotypical ezcap boards you can test this by connecting an appropriately long wire antenna to the right side of capacitor 17 (on EzTV668 1.1, at least) that goes to pin 1 of the RTL2832U. That's the one by the dot on the chip surface. Apparently even pressing a wet finger onto the capacitor can pick up strong AM stations. This bypasses static protection among other things so there's a chance of destroying your dongle. For gr-osmosdr the parameter direct_samp=1 or direct_samp=2 gives you the two I or two Q inputs.


Differential input

Since then the direct sampling branch has been integrated into main and a number of people have also done balun stuff to use both RTL2832U ADC inputs (usually the two I) in direct sampling mode. Dekar has a page showing how to use an ADSL transformer to generate signal for the ADCs differential input using pin 1 (+I) and 2(-I) on the RTL2832. mikig has a useful pdf schematic with part numbers for using wide band transformers or toroids for winding your own. Here's a series of posts from bh5ea20tb showing how to use a FT37-43 ferrite core. And another example from IW6OVD Fernando. The ADC has a differential/balanced input so this is done mainly for the unbalanced->balanced conversion. But the ADC input pins also have a DC offset so you can't just connect one to GND for that. Impedance matching can be done as well but the impedance isn't known. ~200 Ohms seems reasonable and is mentioned in some of the tuner datasheets. 4:1 baluns that are used for cable-tv might also work, depending on the impedance of your antenna.

Tom Berger (K1TRB) used multiple core materials with trifilar wire and performed tests using his N2PK virtual network analyzer on May 19th (2013).

Hams love type 43 ferrite, but for almost every application, there is a better choice. For broadband HF transformers Steward 35T is generally a better choice. Therefore, I wound a couple transformers and did the comparison. Type 43 and 35T Transformer Material Compared

For my personal tests with direct sampling mode I ordered a couple wideband transformers from coilcraft. The PWB-2-ALB and PWB-4-ALB to be specific. I sampled the PWB-4-ALB for free and ordered 4 of the PWB-2-ALB for ~$10 shipped. Both seem to work fine though I have no means of comparative testing.

If you're particularly interested in HF work then an upconverter would be better than the HF mod. With the mod there will be aliases(*) for any frequency over 14.4 Mhz (1/2 the 28.8 clock rate). And probably other little idiosyncracies. A lot of people chose to just use an upconverter instead. KF7LE wrote up short summaries comparing 16 popular upconverters.

Sample rates

When setting sample rates in your own programs or scripts try to use one of the values shown in, http://cgit.osmocom.org/cgit/gr-osmosdr/tree/lib/rtl/rtl_source_c.cc#n373. If it's an end-user app like SDR# or Gqrx then it handles all this for you in the background. It's handy for writing pyrtlsdr scripts though.

  range += osmosdr::range_t( 250000 ); // known to work
  range += osmosdr::range_t( 1000000 ); // known to work
  range += osmosdr::range_t( 1024000 ); // known to work
  range += osmosdr::range_t( 1800000 ); // known to work
  range += osmosdr::range_t( 1920000 ); // known to work
  range += osmosdr::range_t( 2000000 ); // known to work
  range += osmosdr::range_t( 2048000 ); // known to work
  range += osmosdr::range_t( 2400000 ); // known to work
//  range += osmosdr::range_t( 2600000 ); // may work
//  range += osmosdr::range_t( 2800000 ); // may work
//  range += osmosdr::range_t( 3000000 ); // may work
//  range += osmosdr::range_t( 3200000 ); // max rate
Noise, shielding, and cables.

The plastic cases the dongles ship in leads electrical interference susceptability. It is best to shield them if you can. Acinonyx describes one way to doing this using a single strip of aluminum tape combined with a spring to connect it to the dongle ground. I wrap the entire pcb, except the grounds on the connectors, with kapton tape and then use a single continuous piece of aluminum foil tape to wrap the rest of the dongle. This is easiest with minis. Even sealed with aluminum tape they seem to dissipate heat and reach thermal equilibrium fine in terms PPM error.

Another way to minimize electrical noise is to use a long USB *active* extension cable with hubs at the end and ferrites added. The 10 meter long active USB extension cable I bought seems to decrease the noise floor as compared to directly hooking up to my computer's USB ports. Additionally it lets me place my dongle directly on the antenna feed outside without the signal loss of coaxial cable.

Broadband Antenna

When I want to do some scanning that takes advantage of the tuner's very wide ranges I use three types of antenna: discones, spirals, and horns. Both discones and archimedian spiral antenna can omnidirectionally cover almost the full range of the E4000 tuner but things get a bit too large to go all the way to the 24 Mhz of the R820T. You can refer to the seperate spiral antenna page for construction and technical details. To build my discone I followed Roklobsta's D.I.Y. Discone for RTLSDR.

When using such broadband antenna it is possible to pick up powerful out of tuner band signals due to overloading. You can see an example of how bad this interference can be in raw sample total power measurements over time x frequency in these 2D spectral maps: 1, 2. Or in the 1D spectrum plot below,

The powerful pagers (?) near 155 and 930 Mhz, and the university's multiple 45 watt ~460 Mhz transmitters across the street appear aliased (?) all over into other frequency bands. Nasty. In the future I hope to notch them out with physical filters. The linked plot above is made with this gnuplot format and the csv output of RTLSDR Scanner using 1 second integration times with a wire discone.

The spectra and noise baselines are much cleaner when using directional and resonant antenna instead of wideband omnidirectionals like I've been using to characterize the RFI environment.

patchvonbraun suggested doing a frequency sweep with a shielded terminated resistor and then subtracting that sweeps' results from the antenna scans. RTLSDR Scanner's sweeps for the same range and sample rate always match up on frequencies. So it should be just subtracting the corresponding elements of the sorted value pairs from antenna and resistor using self.spectrum.iteritems() in RTLSDR Scanner or using unix tools with the csv.

Chipset docs, GNU Radio, DSP, and Antenna Links

Page Sections

RTL-SDR Links


Warning: I'm learning as I go along. There are errors. Refer to the proper documentation and original sources first.

GNU Radio *and* RTLSDR Setup

You don't need GNU Radio to use the rtlsdr dongles in sdr mode, but there are many useful apps that depend on it. patchvonbraun has made setting up and compiling GNU Radio and RTLSDR with all the right options very simple on Ubuntu and Fedora. It automates grabbing the latest of everything from git and compiling. It will also uninstall any packages providing GNU Radio already installed first. Simply run, http://www.sbrac.org/files/build-gnuradio, and it'll automate downloading and compiling of prequisites, libraries, correct git branches, udev settings, and more. I had no problems using Ubuntu 10.04 AMD64 or 12.04 32bit.

If you're thinking about trying this in a virtual machine: don't. If you do get it partially working it'll still suck.

As an aside: If you're an OSX user then refer to dekars work for gqrx that contains rtl-sdr, gr-osmosdr, GNU Radio, libUSB, boost and Qt dependencies.

mkdir gnuradio
cd gnuradio
wget http://www.sbrac.org/files/build-gnuradio
chmod a+x build-gnuradio
./build-gnuradio

An (re)install looks like this. It might be useful to save the log output for future reference. Then test it. The test output below is from an old version of rtl_test. Newer versions output is slightly different.

rtl_test -t
Found 1 device(s):
  0:  ezcap USB 2.0 DVB-T/DAB/FM dongle

Using device 0: ezcap USB 2.0 DVB-T/DAB/FM dongle
Found Elonics E4000 tuner
Benchmarking E4000 PLL...
[E4K] PLL not locked!
[E4K] PLL not locked!
[E4K] PLL not locked!
[E4K] PLL not locked!
E4K range: 52 to 2210 MHz
E4K L-band gap: 1106 to 1247 MHz

Once GNU Radio is installed the "Known Apps" list at the rtl-sdr wiki is a good place to start. Try running a third party receiver, a python file or start up GNU Radio Companion (gnuradio-companion) and load the GRC flowcharts. If you're having "Failed to open rtlsdr device #0" errors make sure something like /etc/udev/rules.d/15-rtl-sdr.rules exists and you've rebooted.

Updating

When updating you can just repeat the install instructions which is simple but long. But at least this way if there are major changes in the gr-osmosdr in addition to rtl-sdr you'll be fine. This'll do things like ldconfig for you.

If you don't have the patience for a full recompile and there haven't been major gnu radio or gr-osmosdr changes it's much faster just to recompile rtl-sdr by itself. The instructions to do so are at the osmosdr page. It'll only take a few minutes as compared to a few tens of minutes if you're also building gr as in ./build-gnuradio. It's like most cmake projects: mkdir build; cd build; cmake ../ ; make; sudo make install

rtl-sdr supporting receivers, associated tools

Pager stuff

DongleLogger: my pyrtlsdr lib based spectrogram and signal strength log and plotter

Purpose:

Automatic generation of and html gallery creation of wideband spectrograms using multiple rtlsdr dongles to divide up the spectrum. It also produces narrow band total charts, and other visualizations.

(not live): http://erewhon.superkuh.com/gnuradio/live/ - click the spectrograms for time series plot

These scripts cause the rtlsdr dongle to jump from frequency to frequency as fast as they can and take very rough total power measurement. This data is stored in human readable logs and later turned into wideband spectrograms by calling gnuplot. In order to further increase coverage of any given spectrum range multiple instances of the script can be run at once in the same directory adding to the same logs. Their combined output will be represented in the spectrogram.

Details:

I don't know much python but the python wrapper for librtlsdr pyrtlsdr was a bit easier to work with than gnu radio when I wanted to do simple things without a need for precision or accuracy. Actualy receivers with processing could be made with it too, but not by me. This is the gist of what it does,

power = 10 * math.log10(scan[freq]) = scan = self.scan(sdr, freq) = capture = sdr.read_samples(self.samples) = iq = self.packed_bytes_to_iq(raw_data) = raw_data = self.read_bytes(num_bytes)

The pyrtlsdr library can be downloaded by,

git clone https://github.com/roger-/pyrtlsdr.git

I have used the "test.py" matplotlib graphical spectrogram generator that came with pyrtlsdr as a seed from which to conglomerate my own program for spectrum observation and logging. Since I am not very good with python I had to pull a lot of the logic out into a perl script. So everything is modular. As of now the python script generates the spectrogram pngs and records signal strength (and metadata) in frequency named logs. It is passed lots of arguments.

These arguments can be made however you want, but I wrote a perl script to automate it along with a few other useful things. It can generate a simple html gallery of the most recent full spectral map and spectrograms with each linked to the log of past signal levels. Or it can additionally generate gnuplot time series pngs (example) and link those intead of the raw logs. It also calls LTE Cell Scanner and parses out the frequency offset for passing to graphfreq.py for correction. I no longer have it running because of the processor usage spikes which interrupt daily tasks. In the past I'd have rsync updating the public mirror with a big pipe every ~40 minutes.

Modifying pyrltsdr

As it is pyrtlsdr does not have the get/set functions for frequency correction even if I sent the PPM correct from the perl script. Since the hooks (?) were already in librtlsdr.py (line 60-66) but just not pythonized in rtlsdr.py they were easy to add to the library. These changes are required to use frequency correction and make the int variable "err_ppm" available. I have probably shown that I don't know anything about python with this description.

I forked roger-'s pyrtlsdr on github and added them there for review or use, https://github.com/superkuh/pyrtlsdr/commit/ffba3611cf0071dee7e1efec5c1a582e1e344c61. I apologize for cluttering up the pyrtlsdr namespace with such trivial changes but I'm new to this and github doesn't allow for private repositories.

What you should be using instead.

Download

fast version: see below

slow version:

The faster version
Speed ups, Inline C usb reset, and avoiding dongle reinitialization... (less options)
cli switches/options
-dev 1			:: rtlsdr device ID (use to pick dongle)
-g 30			:: gain
-s 			:: interval between center frequencies
-r 2400000		:: sample rate
-d2 /path/here		:: path to the directory to put logs, plots, gallery
-c 751			:: LTC Cell scanner frequency offset correction, takes freq in Mhz of base cell
-w			:: turn on web gallery generation
-p			:: turn on gnuplot time series charts for every freq (don't use to maximize speed)
-m			:: generate full range spectrogram using all.log (this is the most useful thing)
-mr "52-1108,1248-1400,1900-2200"	:: set of frequency ranges to plot as a another spectrogram

These two scripts do fast scans within python from x to y frequency. Enabled it with -fast and make sure to set start and stop frequency with -f1 and -f2. Do not use -flist with this option.

$ while true; do perl radioscan_faster.pl -d2 /tmp/faster -f1 25 -f2 1700 -fast -g 30 -r 2400000 -s 1.2 -m -p; sleep 1; done;
Running graphfreq in non-batch fast mode 25 to 1700 Mhz at 1.2 Mhz spacings.
 Spectrograms and text output disabled.
Using LTE Cell Scanner to find frequency offset from 751 Mhz station...Found Rafael Micro R820T tuner
-44k frequency offset. Correcting -58 PPM.
Generating spectral map.

python ./graphfreqs_faster.py 40000000 2400000 30 -58 /tmp/faster 1700000000
Found Rafael Micro R820T tuner
... (repeat many, many times)

This is an example output "spectral map" (a spectrogram with a silly name).

This example output above shows the overloading effects of using a wideband discone that picks up off-band noise. Each column is made up of small squares colored by intensity of the signal. Since the scripts start at the low frequency and sweep to high there is a small time delay between the bottom and top (see it more clearly zoomed in). And this is represented as the slant of the row. Sometimes strong signals will swamp out others resulting in discontinuities displaying as small dark vertical bands.

Or fast (-fast) scan a smaller range with smaller range (-f1,-f2: 24-80Mhz), with smaller samplerate (-r: 250 Khz) at smaller intervals (-s: 400Khz steps) with a gain of ~30. Only output a large spectrogram of all frequencies to the directory specified with -d2 as spectral-map.png. This example does not use frequency offset correct (-c) for even faster speeds.

while true; do perl radioscan_faster.pl -d2 /home/superkuh/radio/2012-02-02_R820T_Discone_lowfreq -f1 24 -f2 80 -fast -g 30 -r 250000 -s 0.4 -m -p; sleep 1; done;
Running graphfreq in non-batch fast mode 24 to 80 Mhz at 0.4 Mhz spacings.
 Spectrograms and text output disabled.
Generating spectral map.

python ./graphfreqs_faster5.py 24000000 250000 30 0 /home/superkuh/radio/2012-02-02_R820T_Discone_lowfreq 80000000 400000
Found Rafael Micro R820T tuner
Exact sample rate is: 250000.000414 Hz

Combining multiple rtlsdr devices for greater speed

Full

Zoom

By splitting up the spectrum into multiple smaller slices and giving them to multiple dongles the time required for one scan pass can be greatly improved. The above spectrogram is made with 2 dongles, one for the lower half and one for the upper. It is from ryannathans who also contributed the code for for specifying device ID. This is as simple as running the script twice but giving each instance a different "-dev" argument to specify device ID. You can run as many rtlsdr devices with my scripts as you wish (up to the USB and CPU limits). If they are using the same directory (-d2) their log data will be combined automagically for better coverage.

while true; do perl radioscan_faster.pl -d2 /home/superkuh/radio/2013-06-09_multidongle -f1 25 -f2 525 -fast -g 40 -r 2400000 -s 1.2 -m -dev 0; sleep 1; done;
...
Found Rafael Micro R820T tuner
while true; do perl radioscan_faster.pl -d2 /home/superkuh/radio/2013-06-09_multidongle -f1 525 -f2 1025 1100 -fast -g 29 -r 2400000 -s 1.2 -m -dev 1; sleep 1; done;
...
Found Elonics E4000 tuner
Outlier signals skewing your color map scale?

Sometimes I get corrupt samples that show a signal level of +60dB. These skew the scale of the output spectrograms. If I notice that they have occurred during a long run I'll use grep to find them and remove them manually. I replace the signal level with the level of the previous non-corrupt sample. In the future I'll build this kind of outlier removal in to the scripts, or sanity check before writing them.

grep -rinP " (3|4|5|6)\d+\.\d+" *.log

All the incremental improvements in speed I've made above are okay but not very easy to maintain with multiple script types (bash/perl/python). I'm slowly putting together an Inline C based perl wrapper for exposing librtlsdr's functions within a perl script to write this as a standalone in perl. This is slow work because I've never done anything like it before.

rtlsdrperl - a perl wrapper for librtlsdr

I only have the most basic of basics fleshed out right now, but here's some example code. I would have never achieved even this simple task if not for the help I received from mucker on Freenode's #perl.

#!/usr/bin/perl
use Inline C => DATA => LIBS => '-L/usr/local/lib/ -lrtlsdr -lusb';
use warnings;
use strict;

my $fuckingtest = get_device_name(0);
print "Device name: $fuckingtest\n";
my $fuckingtest2 = get_device_count();
print "# Devices: $fuckingtest2\n";

__END__
__C__
const char* rtlsdr_get_device_name(uint32_t index);
char * get_device_name(int count) {
	char* res = rtlsdr_get_device_name(count);
	return res;
}

uint32_t rtlsdr_get_device_count(void);
int get_device_count() {
	int hem = rtlsdr_get_device_count();
	return hem;
}

Older version

graphfreqs.py

You have to have the modified pyrtlsdr with the get/set functions for frequency correction. LTE Cell Scanner should also be installed so the "CellSearch" binary is available. Then download the two scripts above and put them in the same directory. For large bandwidths sampled this feature, ppm error correction, has an unnoticably small effect but I wanted to add it anyway.

To call the spectrogram/log generator by itself for 431.2 Mhz at 2.4MS/s with a gain of 30 and frequency correction of 58 PPM use it like,

python graphfreqs.py 431200000 2400000 30 58

I've disabled the matplotlib (python) per frequency spectrogram plots for frequencies over 1 Ghz because there's not much going on up there. Also, the x-axis ticks and labels become inaccurate for some reason.

Logs and format

The signal strength logs, named by frequency (e.g. 53200000.log), use unix time and are comma seperated with newlines after each entry. In order of columns it is: unix time , relative signal level , gain in dB, PPM correction.

1345667680.28 , -34.65 , 29 , 57
1345667955.59 , -34.67 , 29 , 57
1345668004.37 , -34.55 , 29 , 57
1345668110.06 , -33.88 , 29 , 57

It also generates a log file with all frequencies for use with gnuplot, all.log. This file has unixtime first, then frequency, then gain and ppm error.

1347532002.5 52000000 -14.84 29.0 58
1347532004.88 53200000 -17.84 29.0 58
1347532007.04 54400000 -17.98 29.0 58
1347532009.04 55600000 -19.78 29.0 58
1347532011.02 56800000 -24.04 29.0 58
1347532012.98 58000000 -26.21 29.0 58
1347532014.92 59200000 -25.10 29.0 58
radioscan.pl

The radioscan.pl script is used to automate calling graphfreqs in arbitrary steps. To generate plots and signal strength for 52 Mhz to 1108 Mhz with a gain of 30, sample rate of 2.4MS/s, and an interval between center frequencies of 1.2 Mhz, call it like,

$ perl radioscan.pl -flist "52-1108,1248-2200" -g 30 -r 2400000 -s 1.2
cli switches/options
-flist "52-1108,1248-2200"  :: sets of frequency ranges to scan.
-g 30			:: gain
-s 			:: interval between center frequencies
-r 2400000		:: sample rate
-d1 /path/here 		:: path to where the scripts are if now pwd
-d2 /path/here		:: path to the directory to put logs, plots, gallery
-c 751			:: LTC Cell scanner frequency offset correction, takes freq in Mhz of base cell
-w			:: turn on web gallery generation
-p			:: turn on gnuplot time series charts for every freq
-m			:: generate full range spectral map using all.log
-mr "52-1108,1248-1400,1900-2200"	:: set of frequency ranges to plot as a another spectral map

Because I can use the default directories I keep it running like the below, but anyone else should make sure to set -d2.

$ while true; do perl radioscan.pl -flist "52-1108,1248-2200" -g 30 -r 2400000 -s 1.2 -w -c 751 -p -m -mr "52-1108"; sleep 1; done;

Running pyrtl graphfreq batch job 52 to 1108 Mhz at 1.2 Mhz spacings.
Using LTE Cell Scanner to find frequency offset from 751 Mhz station...Found Elonics E4000 tuner
42.6k frequency offset. Correcting 56 PPM.
Generating spectral map.
Generating another spectral map over only 52-1108.

python ./graphfreqs_offset.py 52000000 2400000 30 56
Found Elonics E4000 tuner
python ./graphfreqs_offset.py 53200000 2400000 30 56
Found Elonics E4000 tuner
python ./graphfreqs_offset.py 54400000 2400000 30 56
Found Elonics E4000 tuner
...
python ./graphfreqs_gnuplot.py 316000000 2400000 30 56
Found Elonics E4000 tuner
Dongle froze, reseting it's USB device...
Resetting USB device /dev/bus/usb/001/017
Reset successful
python ./graphfreqs_gnuplot.py 317200000 2400000 30 56
Found Elonics E4000 tuner
..
Generating page, moving images.

starting rsync...
Tuner/USB freeze solution with unplugging
edit: as of Jan 5th 2013, librtlsdr has added soft reset functionality

Since graphfreqs.py's initializing and calling of rtl-sdr happens so frequently there are sometimes freezes. To fix these the USB device has to be reset. In the past I would accomplish this by un and re-plugging the cord manually. But that meant lots of downtime when I was away or sleeping. So, I've added in a small C program to the perl script using Inline::C that exposes a function, resetusb(). It is used if the eval loop around the graphfreqs call takes more than 10 seconds. This means you need Inline::C to run this script. To look at the original C version with a good explanation of how to use it click here.

sub donglefrozen {
	my $usbreset;
	my @devices = split("\n",`lsusb`);
	foreach my $line (@devices) {
		if ($line =~ /\w+\s(\d+)\s\w+\s(\d+):.+Realtek Semiconductor Corp\./) {
			$usbreset = "/dev/bus/usb/$1/$2";
			resetusb($usbreset);
}}}
__END__
__C__
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <sys/ioctl.h>
#include <linux/usbdevice_fs.h>

int resetusb(char *dongleaddress)
{
	const char *filename;
	int fd;
	int rc;
	filename = dongleaddress;
	fd = open(filename, O_WRONLY);
	if (fd < 0) {
		perror("Error opening output file");
		return 1;
	}
	printf("Resetting USB device %s\n", filename);
	rc = ioctl(fd, USBDEVFS_RESET, 0);
	if (rc < 0) {
		perror("Error in ioctl");
		return 1;
	}
	printf("Reset successful\n");
	close(fd);
	return 0;
}

My 11 GHz solar intensity interferometer that uses an rtlsdr receiver w/gnuradio

$75 2x 18" satellite dishes w/mounts shipped
$10 2x Ku LNFB (PLL321 S-2, ~30ppm error)
$20 rtlsdr receiver (e4k ezcap, ~30ppm error)
$15 power combiner (cheaper ones work too)
$5 coaxial power injector (LPI 2200)
$20 coaxial power supply (LPI 188PS) + diodes
$20 100ft RG6 quadshield + connectors

Interferometry is possible as long as it is done before the rtlsdr gets involved. I am basically copying the MIT Haystack Very Small Radio Telescope but replacing the imprecise hardware integrator with an rtlsdr dongle and software defined radio. It is a clever, non-simple, interferometer system that uses the frequency error difference in the 11 GHz LNB clocks to create a beat frequency in the total power integrated. There are *no nulls* possible but the fringe modulation can still be read out as variations in count of bins that contain the beat frequency (in the total power fft). The frequency error in the PLL-based satellite LNBs is about 30 PPM which results in beat frequencies of ~100 KHz. For a detailed mathematical explanation see MIT Haystack's Basic VSRT Operation.pdf . The intensity interferometry technique was originally developed by Twiss & Hanbury-Brown or Roger Jennison. "The Early Years of Radio Astronomy: Reflections Fifty Years after Janskys Discovery" by W T Sullivan (2005) is an excellent source about Hanbury Brown and Twiss's side of it. The chapter "THE INVENTION AND EARLY DEVELOPMENT OF THE INTENSITY INTERFEROMETER" is fascinating. It covers not only the technical concepts but also historical context, detailed hands-on implementations, and other personal anectdotes. Also check out Jennison's book "Radio Astronomy" (1966)) as he invented the process of closure phase which uses a third antenna element to self-calibrate the array and resolve positional ambiguities from path induced phase shifts.

The correlation is done with a regular satellite stripline power combiner at the intermediate frequency (IF, ~950-1950 MHz) and then an rtlsdr dongle is used to measure the total power of a 2.4 MHz bandwidth of the intermediate frequency range. I use a gnuradio-companion flowgraph to take the total power and then do a fourier transform of the total power. In this fourier transform the fringes show up as a modulation of the count in the FFT bins which correspond to the difference in frequency between the two downconverters. In my case this is about ~100 KHz.

In the Haystack VSRT memos a line drop amplifier, or two, are sometimes put behind the respective LNBF IF coax outputs or the power combiner. With the rtlsdr dongle and relative short (<10m) baselines of RG6 this isn't required.

The GUI allows for setting the exact 2.4 MHz bandwidth of the IF range to sample and the total power FFT bin bandpass to where and what the LNBF beat frequency is. The file name is autogenerated to the format,

prefix + datetime.now().strftime("%Y.%m.%d.%H.%M.%S") + ".log"

The time embedded in the filename is later used by a perl script, vsrt_log_timeplot.pl, which converts and metadata tags the binary records to gnuplot useable csv format for making PNG plots.

The electronics and sofware sides are easy but manually repositioning the dishes swamps out the signal of interest. I'll try to follow the Haystack idea of two coupled Diseqc 1.2 compatible motor positioners mounted one on the other. In their design both dishes are mounted on a single PVC tube hooked to one of the positioners with a metal extension. My dishes can't rotate like theirs so I'll have to modify this design a bit. They use a serial relay to "push" the buttons on a physical Diseqc 1.2 motor controller remote. That seems a bit convoluted to me. I will buy a skystar2 (or hopefully cheaper) DVB pci card and under linux send raw Diseqc commands out by calling xdipo which accesses the linux DVB interface. Another alternative Diseqc motor controller would be using a 192 KHz USB soundcard and the DiSEqC Audio Generator software from Juras-Projects. Unfortunately the documentation for the hardware side of the audio generator is 404 now.

Download

Who else helped

I consulted with patchvonbraun a lot for the software/gnuradio side. I would not have guessed I needed to square the values from the beat frequency bins after the first squaring for taking total power. He even made a generic simulator for dual free running clocks LNBF intensity interferometers with a working stripchart in gnuradio-companion. You don't even need to have an rtlsdr device to run it; only an up to date install of gnuradio. It is a great way to understand how to do interferometry without a distributed clock signal.

patchvonbraun's: simulated-intensity-interferometer.grc


Physical

With this setup on a 1 meter baseline and a intermediate tuning frequency of 1.6 GHz IF (10700 MHz+(1600 MHz−950 MHz)= 11350 MHz) then given 70*(c/11GHz)/1m)=1.9 degrees it is not possible to completely resolve the solar disk (~0.5 deg) during drift scans. I have been told that the magnitude goes down in a SINC pattern as you widen the baseline and approach resolving the source but I will not resolve the sun initially. Since total power measures the envelope of the In the VSRT Memos "Development of a solar imaging array of Very Small Radio Telescopes" a computationally complex way to resolve individual action regions is done with a 3rd dish providing "closure" in the array on a slanted north-south baseline in addition to the existing east-west baseline. I try to point my dishes so that the Earth is passing the sun through the beam at ~12:09pm (noon) each day. To aid in pointing a cross of reflective aluminum tape is applied center of the dish. This creates a cross of light on the LNBF feed when it is in the dish focal plane and the dish is pointed at the sun. The picture below is from later in the day, the one of the left shows the sun drifting out of the beam as it sets. I made my LNBF holders out of small pieces of wood compression fit in the dish arm. There are grooves for the RG6 coax to fit ground out with a rotary tool. The PVC collars have slots cut in the back with compression screws going into the wood to set the angle.


The screenshot shows a short run near sunset on an otherwise cloudy day. The discontinuities are me running outside and manually re-pointing the dishes. But it does highlight how the beat frequency of the 2 LNBF varies as they warm up when turned on. It starts down at ~90 KHz but within 10 minutes it rises to ~115 KHz. After it reaches equilibrium the variation is ~ -+1 KHz. I could change the existing 80-120 KHz bandpass to a 110-120 KHz bandpass and have better sensitivity. But that bandwidth is something that has to be found empirically with each LNBF pair and set manually within the GUI for now.

patchvonbraun said it was feasible to identify the frequency bins with the most counts and that there was an example within the simpla_ra code,

"You could even have a little helper function, based on a vector probe, that finds your bin range, and tunes the filter appropriately."

The below close up of indoor testing showing how everything is connected on the rtlsdr side showing the power injector, e4k based rtlsdr (wrapped in aluminum tape), and the stripline based satellite power combiner for correlation. The two rg6 quadshield coaxial lines going from the power combiner to the ku band LNBF are as close to the same length as I could trim them. I use a 1 amp 18v power supply and coaxial power injector to supply power to the LNB and any amplifiers. This voltage controls linear polarization (horiztonal/vertical) and it can be changed by putting a few 1 amp 1N4007 in series with the power line to drop the voltage.

Software

tp-modes.grc produces binary logs that are pretty simple. The count of the LNBF beat frequency bins in the bandpass are saved as floats represented as 4 pairs of hexadecimal. When the integration time is set to the default 1 second then one 4 byte data point is written to the log every 0.5 seconds. I highly recommend not changing this for now. There is no metadata or padding. Here's a screenshot of a run using the utility "bless",

In order to convert the binary logs of 4 byte records into something gnuplot can parse I use a simple perl script,

#!/usr/bin/perl
use warnings;
use strict;

my $data = '/home/superkuh/vsrt_2013.06.13.12.26.47.log';
my $bytelength = 4; 
my $format = "f"; # floats (little endian)
my $num_records;

if ($ARGV[0]) {
	$data = $ARGV[0];
} else {
	print "you need to pass the log file path as an argument.";
	exit;
}

open(LOG,"$data") or die "Can't open log.\n$!";
binmode(LOG);

my $i = 0;
until ( eof(LOG) ) {
	my $record;
	my $decimal;
	read(LOG, $record, $bytelength) == $bytelength
		or die "short read\n";
	$decimal = unpack($format, $record);
	printf("$i,\t$decimal\n", $decimal);
	$i++;
}

Now I have the filename which gives the time the gnuradio-companion grc file started running. This is not the time I hit the record button and started logging. The offset is a second or two. Ignoring that, it is possible to use the start time encoded in the log file name to figure out when a particular measurement was taken. To do that I have to know the interval between entries saved to the binary log.

$ date && ls -l /home/superkuh/vsrt_2013.06.14.12.03.00.log && sleep 60 && date && ls -l /home/superkuh/vsrt_2013.06.14.12.03.00.log
Fri Jun 14 13:05:24 CDT 2013
-rw-r--r-- 1 superkuh superkuh 29644 2013-06-14 13:05 /home/superkuh/vsrt_2013.06.14.12.03.00.log
Fri Jun 14 13:06:24 CDT 2013
-rw-r--r-- 1 superkuh superkuh 30124 2013-06-14 13:06 /home/superkuh/vsrt_2013.06.14.12.03.00.log

((30124−29644)/4)/60 = 2

$ date && ls -l /home/superkuh/vsrt_null.log && sleep 60 && date && ls -l /home/superkuh/vsrt_null.logFri Jun 14 13:44:36 CDT 2013
-rw-r--r-- 1 superkuh superkuh 8 2013-06-14 13:44 /home/superkuh/vsrt_null.log
Fri Jun 14 13:45:36 CDT 2013
-rw-r--r-- 1 superkuh superkuh 488 2013-06-14 13:45 /home/superkuh/vsrt_null.log

((488−8)/4)/60 = 2

To know what time a log record corresponds to, take the time from the filename and then add 0.5 seconds * the index of the 4 byte entry in the binary log. This should be possible to write into the until loop so it outputs time instead of just index $i. The below example is a hacky version of my log parser that does just this. Here's an example output.

# UTC Epoch	# Beat Freq Bins
1371229380.0,	1.38292284646013e-06
1371229380.5,	1.37606230055098e-06
1371229381.0,	1.374015937472e-06
1371229381.5,	1.366425294691e-06
1371229382.0,	1.35845414206415e-06
1371229382.5,	1.36476899115223e-06
1371229383.0,	1.36480070977996e-06
1371229383.5,	1.36444589315943e-06
1371229384.0,	1.35775212584122e-06
1371229384.5,	1.36395499339415e-06
1371229385.0,	1.35322613914468e-06
1371229385.5,	1.36412847950851e-06
1371229386.0,	1.36531491534697e-06
1371229386.5,	1.3664910056832e-06
1371229387.0,	1.36144888074341e-06
1371229387.5,	1.35596496875223e-06
1371229388.0,	1.35830066483322e-06
1371229388.5,	1.3654090480486e-06
1371229389.0,	1.358990175504e-06
1371229389.5,	1.37098015784431e-06
1371229390.0,	1.387945303577e-06
1371229390.5,	1.38286770834384e-06
1371229391.0,	1.36734763600543e-06
1371229391.5,	1.36036248932214e-06
...
#!/usr/bin/perl
use DateTime;
use warnings;
use strict;

# ./vsrt_log_timeplot.pl /home/superkuh/vsrt_2013.06.14.12.03.00.log > whee2.log
# gnuplot> plot "./whee2.log" using 1:2 title "VSRT Test" with lines

my $data = '/home/superkuh/vsrt_2013.06.13.12.26.47.log';
my $bytelength = 4; 
#my $format = "V"; # oops, not this unsigned 32 bit (little endian)
my $format = "f"; # float
my $num_records;

if ($ARGV[0]) {
	$data = $ARGV[0];
} else {
	print "you need to pass the log file path as an argument.";
	exit;
}

my $dt; # declare datetime variable globally
extracttime($data); # $dt now has date object.

open(LOG,"$data") or die "Can't open log.\n$!";
binmode(LOG);

my $i = 0;
until ( eof(LOG) ) {
	my $record;
	my $decimal;
	read(LOG, $record, $bytelength) == $bytelength
		or die "short read\n";

	$decimal = unpack($format, $record);

	# This is a stupid/fragile way to deal with datetime
	# not having enough precision. It only works if the
	# record to record interval is always 0.5 seconds.
	my $recordtime = $dt->epoch();
	if (0 == $i % 2) {
		printf("$recordtime.0,\t$decimal\n", $decimal);
	} else {
		printf("$recordtime.5,\t$decimal\n", $decimal);
	}

	$dt->add( nanoseconds => 500000000 );
	$i++;
}

sub extracttime {
	my $timestring = shift;
	# /home/superkuh/vsrt_2013.06.13.12.26.47.log
	$timestring =~ /(\d{4}\.\d{2}\.\d{2})\.(\d\d\.\d\d\.\d\d)/;
	my $year_month_day = $1;
	my $time = $2;

	my ($year,$month,$day) = split(/\./, $year_month_day);
	$time =~ s/\./:/g;
	my ($hour,$minute,$second) = split(/:/, $time);

	$dt = DateTime->new(
		year       => $year,
		month      => $month,
		day        => $day,
		hour       => $hour,
		minute     => $minute,
		second     => $second,
		time_zone  => 'America/Chicago',
	);

	$dt->set_time_zone('UTC');
	return 1;	
}

Now I just have to make up a good gnuplot format and integrate the calls into the perl script.

But where are the fringes?!

Okay, I admit it. I don't have any yet. I'm getting there, though. Anyway, when I get all the software written and do start getting multiday averaged data and piping it into gnuplot this what I might see with respect to fringe modulation of counts in the FFT beat frequency bins.

70*(c/11GHz)/1m) = 1.9 degree ~3dB beamwidth
(15 deg/hour)/(1.9 deg) = 7.9/hour 
(7.9/hour)/(60 min/hour) = 0.132 fringe/minute

That doesn't resolve the sun and I'll need to expand my baseline to ~4m sometime.

70*(c/11GHz)/4m) = 0.48 degree ~3dB beamwidth
(15 deg/hour)/(0.48 deg) = 31.25/hour 
(31.25/hour)/(60 min/hour) = 0.52 fringe/minute

Decoding Pager Data with multimon and GRC receivers

Written by Thomas Sailer, HB9JNX/AE4WA, multimon (multimon.tar.bz2) supports decoding a large number of pager modulations.

On June 29th 2012 dekar told me about his updated fork of multimon, multimonNG, with better error correction and more modulations supported. As of right this instant those on 64bit linux should just use the existing makefile and *not* qmake or qt-creator to compile it. For the windows users (or anyone wanting more info) there's a precompiled version and blog post. Make sure to disable all the demodulators you don't need. I think especially ZVEI is quite spammy. This and this is what pocsag sounds like if you're wondering.

When I originally started playing and wrote this there were only a couple options for rtlsdr receivers to use with the multimon decoder. I used patchvonbraun's multimode to save .wavs and dekar's pager example GRC I modified for OsmoSDR sources linked below for raw, real time decoding. Lately (as of late 2012/13) a large number of receivers have been released that don't depend on GNU Radio. rtl_fm is one and there's an example usage below.

real time decoding rtl_fm

rtl_fm -f 930.353e6 -g 100 -s 22050 -l 310 - |multimon -t raw -a POCSAG512 -a POCSAG1200 -a POCSAG2400 -f alpha /dev/stdin

real time decoding w/dekar's pager_fifo

Dekar's multimonNG, a fork with improved error correction, more supported modes, and *nix/osx/windows support. In the screenshots below the signal is not pocsag. I thought it might be zwei but now I'm not so sure it's even pager data. Test samples of pocsag that Dekar links on his blog decode just fine.


pager_fifo_web.grc 
mkfifo /tmp/pager_fifo.raw
./multimonNG -t raw /tmp/pager_fifo.raw
gnuradio-companion pager_fifo_web.grc

In order to decode the pager data in real time you should use a first-in first-out file (fifo). Dekar's pager_fifo is designed to do that but you'll need to set the correct file paths for the File Sink yourself. In the copy downloadable here the File Sink's path is set to "/tmp/pager_fifo.raw". You should be able to run it without editing once you've made that fifo. Make sure to start multimon reading the fifo before you begin GRC and execute the receiver.

In my personal copy of dekar's pager_fifo the file and audio sinks are enabled while the waterfall, wav, and other sinks are disabled. To enable the disabled (grey) block select them and press 'e' ('d to disable). The audio sink is set to pulseaudio ("pulse").

gqrx install notes

When I wrote this up the original version by csete didn't support the hardware yet but mathis_, phirsch, Hoernchen, and perhaps others I've missed from ##rtlsdr on freenode had added librtlsdr support to gqrx; their repos are still listed by commented out. These days csete has added in rtlsdr support so you can use his original repository. 

#git clone https://github.com/phirsch/gqrx
# matthis is the only version I've personally tested (old)
git clone https://github.com/mathisschmieder/gqrx
# the original; supposed to have librtlsdr support now (new)
git clone https://github.com/csete/gqrx.git
cd gqrx 
# on Ubuntu, sudo apt-get install qtcreator , if you don't have it.
qtcreator gqrx.pro 	# press the build button (the hammer)
# Avoid qtcreator doing it manually.
qmake
make

./gqrx

Use with Ubuntu 10.04 and distros with old Qt < 4.7

You will almost certainly not get this error. But, someone might, so I'm leaving it here to be indexed.

If you're like me and run an older distribution then your Qt libraries will be out of date and lack a function required for generating the name of the files to be saved when recording.

/home/superkuh/app_installs/gnuradio/gqrx/gqrx/qtgui/dockaudio.cpp:100: error: ‘currentDateTimeUtc’ is not a member of ‘QDateTime’

Initially I thought it was a qtcreator thing so I tried to get more information by doing it manually,

qmake
make
g++ -c -pipe -O2 -I/usr/local/include/gnuradio -I/usr/local/include -I/usr/local/include -I/usr/local/include/gnuradio -D_REENTRANT -D_REENTRANT -I/usr/include/libusb-1.0 -Wall -W -D_REENTRANT -DQT_NO_DEBUG -DQT_NO_DEBUG_OUTPUT -DVERSION="\"0.0\"" -DQT_NO_DEBUG -DQT_GUI_LIB -DQT_CORE_LIB -DQT_SHARED -I/usr/share/qt4/mkspecs/linux-g++ -I. -I/usr/include/qt4/QtCore -I/usr/include/qt4/QtGui -I/usr/include/qt4 -I. -I. -o dockaudio.o qtgui/dockaudio.cpp
qtgui/dockaudio.cpp: In member function ‘void DockAudio::on_audioRecButton_clicked(bool)’:
qtgui/dockaudio.cpp:100: error: ‘currentDateTimeUtc’ is not a member of ‘QDateTime’

make: *** [dockaudio.o] Error 1

To get it to compile on these systems you'll have to do the below. (edit: This little change is now added into phirsch's.)

Ubuntu 10.04 has old Qt libs and gqrx uses a function call not in them. So, while I was waiting for Qt 4.74 to compile I decided to try a hack. I removed that function call with a static string of text. [edit] I later found comparable functions for Qt 4.6 and older.

If you are using qtcreator like the docs suggest you can double click on the error and go to the line. If not, it was in ./Sources/qtgui/dockaudio.cpp replace,

void DockAudio::on_audioRecButton_clicked(bool checked)
{
    if (checked) {
        // FIXME: option to use local time
        lastAudio = QDateTime::currentDateTimeUtc().toString("gqrx-yyyyMMdd-hhmmss.'wav'");

With something like this.

void DockAudio::on_audioRecButton_clicked(bool checked)
{
    if (checked) {
        // FIXME: option to use local time
        // use functions compatible with older versions of Qt.
        lastAudio = QDateTime::currentDateTime().toUTC().toString("gqrx-yyyyMMdd-hhmmss.'wav'");

And it'll compile and run correctly on my specific machine.

Compiling LTE Cell Scanner and LTE Tracker on Ubuntu 10.04

Before starting make sure to have a fortran compiler, FFTW, BLAS, and LAPACK libraries installed from the repositories.

sudo apt-get install automake autoconf libtool libfftw3-3 libfftw3-dev gfortran libblas3gf libblas-dev liblapack3gf liblapack-dev libatlas-base-dev

If you're using 12.04 just follow the instructions on the github page and everything is trivial. For 10.04 (lucid) users the the initial hurdle is cmake. LTE Cell Scanner requires cmake 2.8.8 and Ubuntu 10.04 only has 2.8 the finding of BLAS and LAPACK libraries will fail like,

CMake Error at CMakeLists.txt:1 (CMAKE_MINIMUM_REQUIRED):
  CMake 2.8.4 or higher is required.  You are running version 2.8.0.

Until you open CMakeList.txt and change the version number on first line to 2.8.0. After fixing that the BLAS and LAPACK issues come in,

cmake ..
-- Found ITPP: /usr/lib64/libitpp.so
CMake Error at /usr/share/cmake-2.8/Modules/FindBLAS.cmake:45 (message):
  FindBLAS is Fortran-only so Fortran must be enabled.
Call Stack (most recent call first):
  CMakeLists.txt:29 (FIND_PACKAGE)

You can see my installation notes before I figured it out. To fix it I searched for people complaining of similar problems on other projects and then replaced my *system* files with theirs, FindBLAS.cmake.

sudo cp /usr/share/cmake-2.8/Modules/FindBLAS.cmake /usr/share/cmake-2.8/Modules/FindBLAS.cmake.bak 
sudo cp FindBLAS.cmake /usr/share/cmake-2.8/Modules/

LAPACK will also fail this way. I used this arbitray cmake file, http://code.google.com/p/qmcpack/source/browse/trunk/CMake/FindLapack.cmake?r=5383. And this is a local backup in case that disappears.

sudo cp /usr/share/cmake-2.8/Modules/FindLAPACK.cmake /usr/share/cmake-2.8/Modules/FindLAPACK.cmake.bak
sudo FindLAPACK.cmake /usr/share/cmake-2.8/Modules/FindLAPACK.cmake

After fixing the cmake issues compile and install the latest IT++ (ITPP 4.2). Make sure to completely remove the old ITPP 4.0.7 libraries from the Ubuntu repository. When LTE Cell scanner compiles you can go back and restore the .bak cmake files. The rate of scan is about 0.1 Mhz per 10 seconds.

./CellSearch -v -s 751e6 -e 751e6
LTE CellSearch v0.1.0 (release) beginning
  Search frequency: 751 MHz
  PPM: 100
  correction: 1
Found Elonics E4000 tuner
Waiting for AGC to converge...
Examining center frequency 751 MHz ...
Capturing live data
  Calculating PSS correlations
  Searching for and examining correlation peaks...
  Detected a cell!
    cell ID: 414
    RX power level: -17.0733 dB
    residual frequency offset: 43592.8 Hz
  Detected a cell!
    cell ID: 415
    RX power level: -20.8041 dB
    residual frequency offset: 43592.3 Hz
  Detected a cell!
    cell ID: 209
    RX power level: -28.8524 dB
    residual frequency offset: 43581.2 Hz
Detected the following cells:
C: CP type ; P: PHICH duration ; PR: PHICH resource type
CID      fc   foff RXPWR C nRB P  PR CrystalCorrectionFactor
414    751M  43.6k -17.1 N  50 N one 1.0000580496943698439
415    751M  43.6k -20.8 N  50 N one 1.0000580490797574829
209    751M  43.6k -28.9 N  50 N one 1.0000580342133056355

Both positive and negative frequency offsets happen, but rarely in the same dongle.

LTE Tracker I haven't used as much yet (recently released) but it is included in the github repository cloned initially and should be compiled as well if you did the above. Check out the authors site for videos of it's use since an ascii paste of the ncurses like interface wouldn't tell you much. But... the start looks like this,

./LTE-Tracker -f 751e6
LTE Tracker v1.0.0 (release) beginning
  Search frequency: 751 MHz
  PPM: 120
  correction: 1
Found Rafael Micro R820T tuner
Calibrating local oscillator.
Calibration succeeded!
   Residual frequency offset: -48937.5 Hz
   New correction factor: 0.99993484110674779597
Searcher process has been launched.

Slightly altered GNU Radio Companion flowcharts

"The GUI stuff in Gnu Radio was rather an afterthought. Nobody really expected that you'd use it to build actual applications, but rather just use it as a way of making "test jigs" for your signal flows."

This section is my notes on how I made basic examples work, and how I edited those examples in very simple and often broken ways. Also, since gqrx, multimode, and other intergrated receivers came out I don't see any need to update these as things change. Most of this is very old.

While there are links to the originals in the summaries, these descriptions are of the versions modified by me; usually just sample rate and GUI stuff. While the sample rate or tuner width I set may be some large number, it'll become obvious what the limits of each other as you scan about and see the signal folding or mirroring. Using sample rates above 2.4 MS/s with gr-osmosdr is not recommended.

  • FM:
  • SSB:

    • Tips

    If it comes with a python file, try that first before generating one from the GRC file. When tuning, make sure to hit enter again if it doesn't work the first time or tunes to the wrong frequency. Always hit autoscale to start, and for FFT displays try using the "average" settings. I have set all audio sinks to "pulse" (pulseaudio) instead of say, "hw:0,0" (ALSA). You might have to change that. To get a list of hardwareuse "aplay -l". That'll show the various cards and devices. Use the format, "hw:X,Y" where "hw:CARD=X,DEV=Y". Some flowcharts have variables for it, others put it directly in the Audio Sink element. If you hear something interesting you can try comparing it to indentified samples from http://www.kb9ukd.com/digital/ or http://hfradio.org.uk/html/digital_modes.html. or the windows program, Signals Analyzer. Check http://www.radioreference.com/ or http://wireless2.fcc.gov/UlsApp/UlsSearch/searchAdvanced.jsp to see what's in the USA area at a given frequency.

    Multiple Dongles

    There are two ways to specify the use of multiple dongles. The first, correct, way is to set the "Num Channels" in the OsmoSDR Source block to "2" and then specify the device IDs in "Device Arguments" like, "rtl=0 rtl=1". Each specified device is seperate with a space from the previous one.

    The not so correct but still working way is to use multiple OsmoSDR Source blocks with "Num Channels" set to "1" and each with it's respective "Device Arguments" field set to "rtl=0" or "rtl=1", or so on.

    The OsmoSDR Source block has extensive help files at the bottom of it's properties if you scroll down.

    Editing

    To enable a block, select it and press 'e'. To disable a block select it and press 'd'. When disabled blocks will appear darker gray.

    If you open a .grc file and it looks like there are blocks missing (red error highlights and no connections between them) then it is likely the name of the block changed during some GNU Radio update. If your install is more than a month or two old this often happens. Update GNU Radio.

    It's easier to type in 1e6 than 1000000 so use scientific notation when you can in variable fields. If you double click on an element in a flowchart it usually includes a helpful "Documentation:" of most the variables to be set at the bottom. The GUI element grid position is a set of two pairs of numbers: "y,x,a,b" where the first pair "y,x," is position (y row, x column) and "a,b" is the span of the box. If you enter a Grid Position and it overlaps with another element it'll turn red and report the error and where the origin is of the element it overlaps with.

    Use the Grid Position (row, column, row span, column span) to position the graphical element in the window.

    The tab effect is done with notebooks.

    For RTL2832 Source the minimum sample rate is ~800KS/s, it's gr-baz(?) and generally not updated. Use OsmoSDR source. It's under "OsmoSDR", not "Sources" on the right panel). It has a 1MS/s minimum sample rate. It's not recommended to use sample rates above 2.4M.

    In older versions of gr-osmosdr and rtl-sdr I think automagic gain control (AGC) was on all the time so you didn't have to set the gain explicitly in the source in GRC. New versions require that and also require setting the chan 0. freq to something.

    The dongles seem to have noise at their 0Hz center frequency so the best performance is from selecting a band 100-200Khz offset from the center (depending on signal type). patchvonbraun's simple_fm_rcv is a great example of that.

    patchvonbraun's simple_fm_rcv

    The best sounding software I've found for listening to FM is patchvonbraun's Simple FM (Stereo) Receiver. I don't think it is very simple; it includes many advanced FM specific features like extraction of the 19k (pilot) tone next to some commercial FM broadcasts. It used to do RDS, I hear, and older versions checked into CGRAN still have it, but it is removed for simplicitly in this version.

    svn co https://www.cgran.org/svn/projects/simple_fm_rcv
cd simple_fm_rcv/
cd trunk
less README
make
make install
## it'll install to ~/bin/, so I use ~/superkuh/bin below
set PYTHONPATH=/usr/local/lib/python2.6/dist-packages:/home/superkuh/bin
# run the python script
python simple_fm_rcv.py
# or edit it
gnuradio-companion simple_fm_rcv.grc

    lindi's FM receiver

    Original: http://lindi.iki.fi/lindi/gnuradio/rtl2832-cfile-lindi-fm.grc , this was an example posted to ##rtlsdr by lindi. It used a file source which was decoded to wav and saved to disk. Seen in the screenshot above.

    Modified: http://superkuh.com/rtl2832-cfile-lindi-fm_edit.grc , had a frontend GUI and an increased sample rate. Right now the rate of the audio files saved out is... not very useful. But it sounds fine. Seen below.

    3.2 MS/s field of view, tune +-900Khz





    2h20's simple fm receiver

    2.8 MS/s field of view, no fine tuning.

    2h20 made available, with thorough explaination, a bare bones FM (mono) receiver to learn how to use GNU Radio. This was the first one I managed to get to work. Because the original h202's uses the RTL2832 Source and not the OsmoSDR Source you might experience tuner crashes if you scan too quickly. Make sure to un/replug in the dongle after these. It's best just to enter the frequency as a number.

    [Be aware this section of this page was written many months ago when rtl-sdr was different and I had little idea of what I was doing. xzero has since manually added signal seeking to this example.]

    My edit of 2h20's simple receiver does not add much, but I did replace the RTL2832 source with an OsmoSDR source to avoid tuner crashes. I also increased the sample rate to 2.8MS/s (to see more spectrum) and then increased the decimation in the filter from 4 to 8 to compensate so everything still decodes/sounds right. I also remove the superfluous throttle block.



    my offset tuning + recording example

    2.8 MS/s field of view, +-900Khz tuning, +-50Khz fine.

    This takes parts from a bunch of the other example receivers and repurposes them in presumably incorrect but seemingly working ways. It is a basic example of how to offset the tuner 200khz away from the center to avoid the noise there. I started with 2h20's simple tuner's GUI framework and removed almost all of the content. I copied, with inaccurate trial and error changes of sample rate and filter offset, sections of the offset tuning and other advanced bits from simple_fm_rcv and wfm_rx.grc. The tuner is tuned +200Khz. The freq_xlating filter is tuned +200Khz. The the bandpass filter is specified in a variable,

    firdes.complex_band_pass(1.0,1.024e6,-95e3,95e3,45e3,firdes.WIN_HAMMING,6.76)

    The net result is that the frequency of interest comes out of the tuner 200Khz below DC, and the freq_xlater "lifts it up" by 200Khz, and then it's bandpassed.

    I also blindly copied the RF power display, a toggle for saving the audio files out to disk, and a +-900khz tuning slider from other receivers. I added a second 'fine' tune +-50Khz. This is done by setting the frequency of the Xlating FIR filter to,

    freq_offset+fine+finer

    where freq_offset is the frequency offset from center (200Khz in this case), fine is the ID of a wx gui slider for regular tuning, and finer is the same for fine tuning. In order for the frequency display to show the proper value it was correspondingly set to a variable ID cur_freq,

    frequency-fine-finer

    I also made the current frequency display a editable text field so you can tune, copy, and paste. There are good examples of how notebook positioning works and includes simple scripting examples for the file field. This flowchart is simple enough to learn from but includes many elements pulled out of the very complex simple_fm_rcv from patchvonbraun. Without his explanation of the offset process I wouldn't have figured it out. All blocks are layed out by type and GUI elements in the same order as they appear when run. This should help you figure out Grid and Notebook positioning.

    The sound is only "okay". I think the signal is being clipped off at the edges a little bit. I am not sure if it is required to install patchvonbraun's simple_fm_rcv to use this, I do use some of his custom filter stuff.

    Usage

    Use the Waterfall for scanning through channels. Once located, look at the offset from 0 on the bottom display. Use that to set the tuning (and fine) slider and wiggle it till you get the signal crossing the band in the "Second Filter" top display. Switch to FFT view and look at the bottom "First Filter" display, use tuning and fine tuning to center the peak on the "First Filter" display. Or the other way around. It's personal preference. Ignore the noise you see at higher frequencies (900Mhz) at +0.2Mhz baseband. Although sometimes it gets folded in depending on tuning.





    SSB Receiver and data Recorder

    Created by Alexandru Csete OZ9AEC the notes say, "Simple SSB receiver prototype". This comes from the GNU Radio GRC examples repository over at https://github.com/csete/gnuradio-grc-examples/tree/master/receiver

    git clone https://github.com/csete/gnuradio-grc-examples.git

    I changed the way it saves samples for the sister decoder program by adding automatic generation of file names and an on/off tickbox toggle for recording. You might want to change the default directory by editing the variable "prefix". The key was

    "/dev/null" if record == False else capture_file

    in the File Sink 'file' field. I also changed the GUI so it was easier to find signals. Use the saved .bin files with ssb_rx_play to hear. Jumping around in frequency is a lot smoother when reading from disk instead of the dongle.




    Tuners...

    steve|m has used his 13MHz cell-phone clock as a reference for a PLL to generate 28.8MHz. He said he used 1v peak to peak.

    <steve|m> not really, just a picture and a short clip: http://steve-m.de/projects/rtl-sdr/osmocom_clocksource.webm http://steve-m.de/pictures/rtlsdr_external_clock.jpg
<steve|m> a motorola C139

    In the absence of any useful information about the RTL2832U clock here's some information about the R820T's clock system.

    Crystal parallel capacitors are recommended when a default crystal frequency of 16 MHz is implemented. Please contact Rafael Micro application engineering for crystal parallel capacitors using other crystal frequencies. For cost sensitive project, the R820T can share crystal with backend demodulators or baseband ICs to reduce component count. The recommended reference design for crystal loading capacitors and share crystal is shown as below.

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