Let's hear it for AM radio!

NYTimes: A Quest to Save AM Before It’s Lost in the Static http://nyti.ms/1aX6J4Y

So *you* have radio interference problems?

If you want to work at the National Radio Astronomy Observatory at Green Bank, WV (my stomping ground in ancient times), you better be prepared to leave your technology behind.  It's a little ironic, because they have some of the most powerful computers, receivers, and electronics you would ever hope to use, but all the local equipment is rigorously RFI-suppressed and tested in anechoic chambers before it is installed.

Check out "The Enemy Is Us" (pdf).

Added: NRAO Green Bank is near the center of the National Radio Quiet Zone.  This is a much larger area (13,000 sq. miles) where all radio emitters by law have to be coordinated to minimize impact at NRAO.

Luddite Cellphone Report

For a few years, I've been telling folks about how I've gone from a $100/mo. smart phone service to  $10-15, non contract, on a barebones Tracfone device.  I don't need e-mail and Internet connectivity when on the hoof, and I have a Nexus 7 tablet for navigation and portable use. Lately, we've had a weird sequence of events that got me to re-evaluate, but the situation is stabilizing now.

The story outline:

1. Noticed that my car's Bluetooth hands-free system isn't functioning.  After a few days,
2. Leaning over to check my pool water, and my Tracfone fell out of my pocket into the deep end.
3. Phone is retrieved after 5 minutes and placed aside to dry out.  Not much hope, as my last Tracfone suffered the same fate and never came back.
4. Recalled that at least one smart phone is now being advertised as waterproof (or resistant?).  Maybe that would be a good one to have?  It would be nice to have mobile yelp and other services like my friends all seem to have...
5. Trying to do some banking business, I discover that I'm blocked because I signed up for 2-factor authentication.  I can't add my wife's phone to the list without receiving a code on my dead phone.  (I could call the bank about this, but that's a last resort.)
6. Google's 2-factor process at least allows me to use one of my one-time pass codes since, thankfully, I haven't lost my wallet.  Anyway, I better get a phone back with my old number asap.
7. The quickest and easiest way to get my number working again is to go back to Tracfone.  I ordered a reconditioned LG.
8. Phone arrives, costing a little over $20 including overnight air.  It wants me to charge for "5 hours", but charging is complete after about 2 hours.
9. Now to the T'phone website to register the new unit and hopefully snag my old number back. End up with a human operator of uncertain nationality talking through a horrendous phone circuit.  She said many things that I did not understand, but finally it seemed we agreed on the basics.  (I hope I did not agree to sell my firstborn.) My number should be effective overnight.  Actually, it only took an hour or so.
10. The new phone became registered in stages.  At first, I could dial out, but not receive calls.  Then it seemed I could send text message, but not receive them.  After 1-2 days, we seem to be fully registered wherever cellphones get registered.
11. Car's hands free Bluetooth is still bust.  I'm guessing that repair will either be free (find the right reset button) or probably 10X the cost of the new phone.

So I'm outfitted with a new (old) phone that is rather snazzier than my previous Motorola W376g.   Still no email, no yelp, etc. but it's a phone.

Raspberry/Beagle/Core Benchmarks

Measured the other day using iPython:

iPython's "timeit" function is hardly the last word in benchmarking, but it can be very useful if you're thinking about Python applications.  Raspberry Pi is very powerful compared to Arduino, say, but very slow compared to modern desktop machines.   No surprises, but I haven't seen relative benchmarks before.

Lousy Saturday on 40 meters

Solar weather (M class flare) makes the low HF bands very quiet this morning! Some day I have to dig in and understand the scale on this map.  It says we're affected by "1 dB" on 40 meters, but I'd say it's more like 30 dB from listening on the band.

Check http://www.swpc.noaa.gov/drap/global.html for the latest.

Raspberry Pi - 30X more time for coffee

alliedelec.com

My Raspberry Pi is benchmarking about 30X slower than one thread (out of 8) on my desktop Core i7 processor. It's an interesting challenge to do real-time Python / wxWidgets programming on the little guy, but we're making progress.

Cable to U-Verse and back again

Executive summary: AT&T U-Verse out, Comcast cable in.

I've been living as an Amateur Radio operator with AT&T's U-Verse service for about 18 months.  It was a great experiment, to see whether ham HF operation could be compatible with U-Verse's VDSL2 signalling.

VDSL2 delivers a bit stream over channels stretching from a low frequency to over 8 MHz, so it was a challenge to work at power levels over 50 W or so in the 160, 80, or 40 M bands.  We tried lots of things -- ferrites everywhere, shielding, etc.  At the same time, AT&T's technology improved, with higher bit rates and more tolerant modems.  We weren't too unhappy as U-Verse customers -- but that was only because I don't spend a lot of time on the air (especially QRO) during TV viewing hours.

Still, I have grown tired of having to think too much about my TV, Internet and phone service.  They should just work!  Even for radio amateurs.  Back to the cable world -- Comcast.

The problems with Comcast will undoubtedly come.  Maybe they'll throttle me if I don't watch enough NBC shows. But in 2 years, maybe we'll see Google or Verizon or somebody offering something more attractive?  Stand by.

KX3 IQ & Python SDR

It's a work in progress, but here's a shot of my Python / wxPython / Numpy "panadapter" display for the Electraft KX3.  The KX3 provides a very nice IQ output (wideband, quadrature audio), covering +/- 24 kHz around the VFO tuning frequency.

I have long been interested in building an SDR software backend using Python et al.   Two principles: (1) You don't understand it if you haven't coded it, and (2) Python is the quickest and often best way to put together complicated software.  It's most at home on Linux systems, but it is not hard to port most applications to Windows.  (Not quite so easy to port: hardware-oriented stuff like audio and Ethernet.)

Like most "friendly" apps, you find that 95% of the work goes into the display and user interface.  The numerical part is almost trivial, using Numpy:

    data = np.array(iqdata[::2] + iqdata[1::2]*1j)
    z = np.roll( fft.fft(data), SIZEC/2)  # place center freq in center
    pwrwork = pwrwork + np.square( np.absolute(z) )

The total code size is about 590 lines at this point.

This application (kx3iq.py) is really a remote control app.  I "beam" the IQ data from the KX3 via my Beagleboard XM and a UDP Ethernet stream to the Python app across the room, with Hamlib rigctld provide rig control.  Using 16 bit 48 kHz sampling, that's a data rate of ~200 kB/s without any compression -- doable over most ISP's these days, if you want a long distance remote.