RTL-SDR Buying Tips

[This was originally posted to a mailing list.]

First, a good starting point on RTL-SDR is the blog site www.rtl-sdr.com.

(I've mentioned it here before and forwarded some relevant posts about things you can do with an SDR such as the RTL-SDR.)

The RTL-SDRs are almost all the same chinese, ultra cheaply made receivers in the range of $15-25.   It isn't so much about which device is trustworthy, it's what tuner chip does it have.

At this point, I suggest getting one with the R820T2 tuner which is newer, seems to perform a little bit better, but costs around $5 more than the others.  IF you get an R820T (not T2) that will do fine as well.

Places that "specialize" in RTL-SDR and aren't too overpriced are:

• Nooelec, http://www.nooelec.com/store/,  They also sell through Amazon.
  
  Their "NESDR Mini 2 SDR" was mentioned on the net $25.  It has the R820T2 tuner chip.  It's not clear if they upgraded any of the other components other than the included mini-whip antenna which you will probably replace.
  
  http://www.nooelec.com/store/sdr/nesdr-mini2-rtl2832u-r820t2.html
  
•  RTL-SDR.com is also selling their own branded R820T2 usb dongles.   They also sell through Amazon.  They claim upgraded components  and a better oscillator (though not temperature controlled) than the usual ones which can easily have a -75 to +75 PPM error.

At this point, almost all of the devices come with an MCX connector so you will need an MCX adapter to hook it up to a real antenna. Both NooElec and RTL-SDR.com's amazon store have MCX adapters.

Also if you don't have any, get some USB extension cables (A male to A-female) around 10 ft in length.  These devices have no shielding, so you want to get them as far away from your computer as you can while sticking within USB length limits.

Try to get a good quality USB extension cable with a ferrite core near the end to cut some of the noise.  You might also want to buy some additional snap on ferrite cores.

Note: The frequency range on these is about 24 Mhz - 1,700 Mhz so you won't be able to do any HF with the exception of 10 meters and maybe 12 meters.  An upconverter can be used if you want to receive HF.

If you connect the RTL-SDR to an outdoor antenna, keep in mind that almost all of these devices have no viable ESD protection.

NBEMS, Radios and Digital Modes: Getting the Message.

Here's a screen shot from a recent Thursday night digital radio net that might help give you an idea of what it is all about if you haven't tried it.

The screen shot shows a received radiogram form as it would look on paper displayed on an Android tablet or phone.

Note: The only equipment used to receive this was an handheld radio (HT) and an Android Tablet. No cable, or interface, was used between the tablet and the HT.   The tablet's microphone decoded the audio coming out of the HT's speaker.

The app on the tablet is AndFlMsg which is a free Android application that implements a some parts of what's available in the FLdigi suites.

While in this case, the information for the form could have been relayed by voice, it could have easily been a picture, spreadsheet, or other file that would be difficult or impossible to relay by voice if the only available infrastructure was a radio.

Standard Container Manifesto

If you haven't seen it, see the  "Standard Container Manifesto" below.   It might help you understand some of the current buzz around container technology.   This one was added to the Docker README at one point but has been since removed.   There are better but longer descriptions.  

Note: to appreciate this, it helps to have been involved in the struggles of delivering enterprise IT where one of the core challenges, (if not the fundamental problem), is trying to get away from everything being somewhat different because it's all built by hand.

Oh, and if you aren't familiar with the story of the standard shipping container and its impact on global commerce, this looks like a reasonable overview: http://www.nytimes.com/2006/03/23/business/23scene.html?_r=0

1. STANDARD OPERATIONS

Just like shipping containers, Standard Containers define a set of STANDARD OPERATIONS. Shipping containers can be lifted, stacked, locked, loaded, unloaded and labelled. Similarly, standard containers can be started, stopped, copied, snapshotted, downloaded, uploaded and tagged.

2. CONTENT-AGNOSTIC

Just like shipping containers, Standard Containers are CONTENT-AGNOSTIC: all standard operations have the same effect regardless of the contents. A shipping container will be stacked in exactly the same way whether it contains Vietnamese powder coffee or spare Maserati parts. Similarly, Standard Containers are started or uploaded in the same way whether they contain a postgres database, a php application with its dependencies and application server, or Java build artifacts.

3. INFRASTRUCTURE-AGNOSTIC

Both types of containers are INFRASTRUCTURE-AGNOSTIC: they can be transported to thousands of facilities around the world, and manipulated by a wide variety of equipment. A shipping container can be packed in a factory in Ukraine, transported by truck to the nearest routing center, stacked onto a train, loaded into a German boat by an Australian-built crane, stored in a warehouse at a US facility, etc. Similarly, a standard container can be bundled on my laptop, uploaded to S3, downloaded, run and snapshotted by a build server at Equinix in Virginia, uploaded to 10 staging servers in a home-made Openstack cluster, then sent to 30 production instances across 3 EC2 regions.

4. DESIGNED FOR AUTOMATION

Because they offer the same standard operations regardless of content and infrastructure, Standard Containers, just like their physical counterpart, are extremely well-suited for automation. In fact, you could say automation is their secret weapon.
Many things that once required time-consuming and error-prone human effort can now be programmed. Before shipping containers, a bag of powder coffee was hauled, dragged, dropped, rolled and stacked by 10 different people in 10 different locations by the time it reached its destination. 1 out of 50 disappeared. 1 out of 20 was damaged. The process was slow, inefficient and cost a fortune - and was entirely different depending on the facility and the type of goods.
Similarly, before Standard Containers, by the time a software component ran in production, it had been individually built, configured, bundled, documented, patched, vendored, templated, tweaked and instrumented by 10 different people on 10 different computers. Builds failed, libraries conflicted, mirrors crashed, post-it notes were lost, logs were misplaced, cluster updates were half-broken. The process was slow, inefficient and cost a fortune - and was entirely different depending on the language and infrastructure provider.

5. INDUSTRIAL-GRADE DELIVERY

There are 17 million shipping containers in existence, packed with every physical good imaginable. Every single one of them can be loaded on the same boats, by the same cranes, in the same facilities, and sent anywhere in the World with incredible efficiency. It is embarrassing to think that a 30 ton shipment of coffee can safely travel half-way across the World in less time than it takes a software team to deliver its code from one datacenter to another sitting 10 miles away.
With Standard Containers we can put an end to that embarrassment, by making INDUSTRIAL-GRADE DELIVERY of software a reality.

Better PC Sound Card Oscilloscope software (windows).

TL;DR - Visual Analyzer, PC Sound Card Oscilloscope software.  Nice spectrum analyzer.  Worth checking out.   http://www.sillanumsoft.org/prod01.htm


Through a really good YouTube Post on using an SDR for Frequency Deviation Measurement on FM transmitters I learned about Visual Analyzer. I should probably do a separate post just on this.

Previously I used Xoscope on Linux and Zeitnitz Soundcard Oscilloscope (http://www.zeitnitz.eu/scope_en).

I had also found, but not used Zelscope, Soundcard Oscilloscope and Spectrum Analyzer.

I originally got some pointers on sound card osclloscopes, from Virginia Tech's Introductory Electronics courses that were based on their Lab in a Box, so that students would have all of their own materials for doing the electronics work without having to be in a physical lab.   See:

Virginia Tech, Experiment 12, Calibrating a Sound Card Oscilloscope

I only went so far with sound card oscilloscopes, because shortly after I started experimenting, the Rigol DS-1052E oscilloscope became available within my budget.  I bought it for $400 direct from China.  The Rigol caused a little bit of a revolution in terms of oscilloscope availability and pricing.

That was all back in 2009 and 2010 when I started reading a lot more about electronics.  In December, 2009, I finally took the exams from my amateur radio license.  I passed both Technician and General with 100% and went back for the Extra Class at the next exam session.  I got one wrong on my Extra.

Of course, the interesting bit that got me here writing this today is that the RTL-SDR stick can be used as the analog (ok radio frequency) front end for a software oscilloscope, spectrum analyzer, deviation meter, etc.  Especially for those of us without much in test equipment.

Intel Atom (Avoton) Mini-ITX (NAS) Server Build Notes

I'm building a mini-ITX NAS style server using Intel's low-power Atom server chip, known as Avoton.  The highlights are 8 cores, 64 GB max memory, yet passively cooled, quiet and low power, 20W TDP.The system's idle power usage without spinning disks is only 14 Watts. This makes it ideal for a SOHO file server, NAS server, lab box, etc.

The system I'm assembling resembles iXsystem's FreeNAS mini.  The main difference is that I went with the Supermicro motherboard instead of the ASRock motherboard.  I'll compare the two motherboards later and/or in a separate blog post.  However, I'll summarize my decision as The ASRock is better if you are going for a pure storage (NAS) box.  I went with the Supermicro as a better general purpose system with USB 3.0 ports and 4 x GbE ports.

Components:

• Supermicro AISAi-2750F Motherboard 
• Supermicro Chassis and 250W Power supply 721TQ-250B
• 16 GB: 2 x 8 GB Crucial SO-DIMM with ECC

Case and Power Supply

One of the most difficult decisions was trying to find a good case and power supply.  There is a lot of poorly designed cases.  There aren't many reviews for mini-ITX NAS-style cases. Through the reviews that are available I found one good choice which is also the same case that iXsystems uses for the FreeNAS Mini, the Ablecom CS-M50. Unfortunately the Ablecom isn't sold in the US directly.  It is primarily sold to OEMs in large quantities. I stumbled around for a while until a kind person clued me in that Supermicro sells the Ablecom CS-M50 as the Superchassis 721TQ-250B. It is even linked from the page for the A1SAi-2750F motherboard and I didn't notice it or assumed it would be yet another crap case.

The summary is the Ablecom CS-M50, aka Superchassis 721TQ-250B is a very nice case with real hot swap drive support. The most detailed reviews are actually for the FreeNAS Mini.  You can also find some reviews searching for the Ablecom CS-M50.

The one problem so far is that the front panel USB ports are USB 2.0.  The A1SAi motherboard has header connectors for USB 3.0, which use a different style header connector.   Currently, I've got no front panel USB ports. I've emailed Supermicro support.

Other People's Builds

Here are some of the sources that I used in making my decisions:

• My FreeNAS Build with The Supermicro A1SAi-i2750f (reddit, billakay)
• Pictures on Imgur
• /My FreeNAS Build with Supermicro A1SAi-2750F (FreeNAS Forum)
  

To Do

• Determine what combination of hypervisors and operating system
• Linux Host + VirtualBox
• Linux Host + KVM
• VMware ESXi
• FreeNAS native FreeBSD
• Solve Front Panel USB port connectivity problem:
• Ideally there is a board from Ablecom, Supermicro or someone else that will give me USB 3.0 front panel ports.
• Alternatively, an adapter cable that gives me USB 2.0 ports would be preferred.

Things I've Learned

• The Supermicro 721TQ-250B case is the same as the Ablecom CS-M50 and is available at retail in the US.
• The AST2400 IPMI BMC controller with fully integrated keyboard, video, and mouse, iKVM is very nice. I could have configured the system out of the box without ever attaching a monitor to.
• The Supermicro/AST default Username and Password for IPMI is UPPER CASE and CASE SENSITIVE.  I mistakenly thought I couldn't access the BMC until I configured it through the BIOS.  The whole problem was the the default username and password were both all upper case.
• As a result, the system is INSECURE out of the box. Change your IPMI/BMC username and password from the default as soon as possible. 
• IPMIView from Supermicro/AST is pretty nice. It is a standalone Java Application. However the web browser interface is just as good or better for a single system.
• The BIOS watchdog feature causes the system to be reset every 5 minutes.  Nothing is logged to the event log.  Don't set it, at least until you understand how to use it.   I think the Linux kernel is setting the hardware watchdog. 
• An improperly seated SO-DIMM, caused the system to hang at BIOS POST, with the code B4.  However there were no beeps and I couldn't find a description of text error codes. The manual only gives the beep codes.

Hopefully this info will help others.

Amateur Radio information on modern social networking.

I'm slowly starting to get some of the appeal of Reddit.    At first I was drawn there by /r/rtlsdr, as there didn't seem to be much info elsewhere.   There is a bit of a digital divide, for on-line sources many hams go to QRZ.com with it's 1990's design and god awful ads flashing all over the page.  Try as you might, some of the old guys can't remember to try anything but QRZ.com. The other big source of info is Yahoo groups which are starting to show their age, but have been made much less useful due to Yahoo trying to figure out how to get more page views.

So two useful places to get answers to amateur radio related info:

1. Reddit: /r/amateurradio  [http://www.reddit.com/r/amateurradio/]
2. StackExchange: ham.stackexchange.com [http://ham.stackexchange.com/]

Decoding 433.92 Mhz devices with RTL_433.

I've been doing a bit of playing with merbanan's rtl_433, which uses the rtl_sdr code to decode signals from 433 Mhz ISM devices that mostly use On-Off-Keying.

So far I've been working on decoding

• Lacrosse TX-7 temperature and humidity sensors, same protocol as TX-3, TX-6.
• DSC wireless security contacts (door/windows, smoke and carbon monoxide detectors)

There is a lot I've learned from playing with the devices using rtl_433 and digging into the code.  I need to write it up because there are almost no instructions.

I've posted the LaCrosse code to github and submitted a pull request to merbanan/rtl_433.

I'm successfully decoding the DSC contacts using a separate Python script that parses the debug output from rtl_433.  I need to write a new pulse decoder for rtl_433 in order to handle the DSC protocol as it's a little different than other pulse or distance coded signals. It doesn't send anything for a zero (0) bit, so there can be long periods (up to 8 bit slots) of no signal.

For more info, contact me if I haven't posted here or to github.

Update: 2015-01-11, merbanan processed a whole bunch of pull requests, including mine, so the LaCrosse TX-7 support is now in the main merbanan/rtl_433 github repository.

I haven't pushed any code for the DSC sensors yet. I have to decide how I want to do the decoder and call back yet.  Anything I push will probably be only be in rct/rtl_433 for a while as it is likely to be experimental.