Friday, April 17, 2015

New Toys: Getting Deeper into Software Defined Radio (SDR) (AirSpy and HackRF Blue)

This is mostly a tease / place holder.   Around Christmas time I decided to get deeper into Software Defined Radio (SDR).  So I ordered an Airspy and a Hack RF Blue.   So far, I've received the AirSpy and am enjoying it very much.  The Hack RF Blue should hopefully be here soon.

Previously I've been using the $15-20 RTL-SDR dongles.  These are very cheap and useful, but plagued with lots of noise, frequency inaccuracies and other problems.  Still they are a great way to get started and start learning.

The AirSpy is a world of difference from the RTL-SDR dongles.  One of the reasons that I bought it was  a number of people who seemed to have deep RF engineering backgrounds seemed to be pretty excited about it.  There are many good reviews available.

I ordered the HackRF Blue to experiment with GNU Radio and especially try some of the transmission capabilities for digital RF hacking.  Initially I'll probably be doing further experiments with simple 433 Mhz devices.

I expect based on receivers that the HackRF's receiver will not be as good as the AirSpy's by a good margin, for sensitivity, selectivity, etc.. However, the HackRF is capable of operating on a much wider frequency range (10 Mhz - 6 Ghz) than the R820T (24 Mhz - 1.8 Ghz) tuner chip inside the AirSpy.

More to come.

Your Radio's Reverse button / Quickiy Checking the Repeater's Input Frequency

[This was originally published on a mailing list, but seemed worth making more widely available.]

Some amateur radios have a "Reverse"(*) button that swaps the repeater input and output frequencies, allowing you to quickly monitor the repeater input and transmit on the repeater output.  When I first started out, I didn't realize the value of this.

The benefits of this feature are:

  • You can quickly listen to the repeater input to determine if someone transmitting is close enough for you to use simplex and free up the repeater.
  • If the repeater isn't working, you can get anyone who is monitoring the repeater's output and is within simplex range, to hear you by transmitting on the repeater's output.
  • During time of malicious interference or other search operation, if we all switch over to monitoring the input and make note of whether we can hear the transmitting station, we can use the information to figure out roughly what area the transmitting station is in.

And finally, the benefit that is relevant to the original topic, hitting the reverse button on many radios is a quick way of seeing what frequency your radio is programmed to transmit on for a repeater.  Your radio display will need to be in a mode to show the frequency rather than the label.

Check your radio's manual to find out how to activate the reverse feature as the button might have an obscure label.  A few common one:
  • Wouxun - It's the scan button.  (A quick press and release).
  • Baofeng UV-5 - The * button.  (A quick press and release). 
  • Many Yaesus - Home/Reverse, HM/RV, Rev, etc.

RTL-SDR Buying Tips

[This was originally posted to a mailing list.]

First, a good starting point on RTL-SDR is the blog site

(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,,  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.
  • 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'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:


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.


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.


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.


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.


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.