Tiny Python Panadapter (QST 4/2014)

[This posting refers to my QST magazine article, "A Tiny Python Panadapter", April, 2014, pp 33-38.  For latest information, see my website. The code repository and a support mailing list are available at SourceForge.net.]

Message from Gary KM5TY:

I'm interesting in putting together my own panadapter, however am not gelling with the idea of the low bandwidth around a signal / amount of spectrum visible with just a sound card. I am thinking that a dedicated sampling board taking in 500kHz to 1.5MHz possibly more would be much more interesting. What do you think of adding such a piece of hardware to a Raspi or Beaglebone? Would the python code be a bottle neck for the data?

Of course, more bandwidth would be very nice.  Unfortunately, to go beyond the simple soundcards for the Tiny Python Panadapter would require considerable new work or expense.  You'd have to consider the following

• Limited CPU power of the tiny cards.  The RPi is already marginal with a 48 kHz sample rate (equivalent to 192 kBytes/sec). [Note added: We've recently made a big improvement for the Pi by downgrading to USB1.1.  The default USB 2.0 can't handle our continuous stream.] You could get to higher rates by starting over with hand-tailored C/C++ code, but there would still be a limit.
• Cost.  The USB soundcards and the RPi/BBB are commodity items that let us do interesting things in the sub-$100 range.  Fast ADC boards are going to be more expensive, if they are available for small platforms -- or you can design & build your own out of chips.
• Proportionality.  The systems you're suggesting are on the market already - like the QS1R and the Flex 6000 line.  These are great products, but expensive.  They are built with high performance FPGA and/or PC-level computing power.  It would be interesting to develop and open-source a free alternative project.  (Some are already out there, like openHPSDR.) But that's well beyond TPP's scope.

On the one hand, it's fun to try to squeeze all the performance you can from a $35 or $45 computer board.  On the other hand, be realistic!  It's so much easier to work with a modern full-size PC.  They are incredibly fast, even the budget models.  How many hours of programming time is it worth to cram the functionality into a tiny board, while saving only a few hundred dollars?  (My time is worth something, isn't yours? :)  In the end, cheap hardware and miniaturization are good, but they're not everything.

It's economic thinking like this that led me to see what could be done with Python on the tiny boards.  At least for me, Python is much "cheaper" to develop with than the C/C++ alternatives.  The added benefit was that it should be easier for "newbies" to pick up and modify.

Merry xmas, already, from QST

Watch "QST Holiday Video 2012" on YouTube

QST & digital QST

The new digital QST edition is now on the web, accessible to ARRL members.  It's a good effort -- at least if you like the new web magazine reading experience.   It is being provided to members as a no-extra-cost addition to the traditional print version.

I hope the pdf version won't go away completely.  That's the format that appears on the annual publications CDROM and on the QST web archives up through 2011. The new format is fine (well, if you like it!) for on-line reading and limited off-line reading, too, but it is a proprietary and DRM-restricted format that probably won't be convenient (if readable at all) 50 years from now.

I was interested in the new QST logos that are cropping up.  There are several variations. One is at the top of this post (I understand it is for the iOS app), and here is another:

 

But I like to look through the QST archives to how QST presented itself in the very earliest days.  The first "logo", from 1915, was this neoclassical marvel:

 

Then, in the late teens and into the twenties, you might have seen this one.  (Color added.)

This is the classical logo for me.  Its block lettering and at least some of the lightning bolts continue into the modern era.  The slogan now says "Amateur Radio" instead of "the Wireless Amateur".  I like this old graphic, but I'm pleased that there is so much continuity in today's version.

Finally, take a look at the first digital QST cover (June, 2012):

Bold and hyperactive design, and presented twice for good measure!

QS1R SDR QST Review

My first-ever product review for QST is coming in the September, 2010, issue.  This is for the Quicksilver QS1R Software Defined Radio.  ARRL members may find it here. [pdf]