Monday, September 29, 2014

More SteppIR Excitement

Matt and Andrew from XX Towers stopped by to repair the latest problem with my 3-element SteppIR beam antenna.

After a recent storm, I discovered high-ish (2.2) SWR on the lower bands and approximately 0 dB Front-to-Back ratio.  Effectively, I had a so-so rotatable dipole.  (Still, it was fine for many contacts with JT65.  Sometimes directivity is over-rated!)

The XX guys found that the inner tapes for one half of the director and one half of the reflector were broken.  As a precaution, I had ordered a complete spare EHU (central steppin motor and tape unit). Matt and Andrew were able to cobble together the two good half units into one full element. So we were able to put up a net of two new passive elements, restoring us to normal SWR and F/B performance, saving us having to order another new EHU and scheduling another service day.  Amazing!

We hope this fix will hold us for some years to come.  Crossing fingers.

Friday, August 15, 2014

Radio Warmup Issues

The WSJT-X software has various uses.  One neat one is to measure frequencies and drifts accurately.


This is the warmup curve for the TenTec Orion 575AT.  Ambient temperature is 75F, and we're starting from that temperature and watching the drift in the apparent frequency of the 15 MHz WWV signal.  The receiver is tuned to 14.999700 USB, so the "correct" response would be a WWV carrier appearing at 300 Hz on the spectrogram.  The WWV carrier (strong red trace) had a starting point (ambient) at about 280 Hz, but this plot begins a little after warmup has started. (The other, blue/yellow traces are modulation sidebands that can be ignored.)

You can see that the initial warmup (fast drift) is over after about 6-8 minutes.  A slow drift continues for another 10-15 minutes, with the apparent frequency stabilizing around 302 Hz.  But after 30-50 minutes, an even slower downward drift comes in that brings the reading down to ~298 Hz. (This is getting into the weeds of ambient temperature stability, etc.  For real statistics, you'd have to repeat all this under various conditions.)

Is this result good or bad?  The initial 20 Hz offset is about 1.3 ppm, while 2 Hz is 0.13 ppm, relative to the 15 MHz signal. The TenTec specification for this radio is +/- 3 ppm over the operating temperature range. The Orion uses a temperature compensated crystal oscillator - TCXO. The oscillator has a screwdriver adjustment for frequency, which I carefully tweaked in 2005.

Clearly, we are in spec at this particular operating temperature, but in fact the specification does not really tell us what to expect in terms of accuracy or stability at any particular ambient temperature. 

I may be in the minority, but I like to be able to use my gear for precise frequency measurement.  (And not as an expensive thermometer!) Some newer rigs are better.  For example, the Flex 6300 and 6500 offer a "0.5ppm TCXO", while the 6700 has a "0.02ppm OCXO" (oven stabilized crystal oscillator.) Flex offers an expensive add-in GPSTCXO option (GPS stabilized TCXO) that claims 5 x 10**-12 stability over 24 hours.

These numbers are helpful, but if you really want to compare time and frequency standards, you need to consider the Allan Variance, which is a measurement of stability on different timescales.  (See informative PowerPoint by H. Fruehauf, or comprehensive Wikipedia article.) What we usually need for precise amateur communications (say using advanced WSJT-style modulation at microwave frequencies) is stability over tens of minutes.  The vendors' specs really don't tell you that. 

Monday, July 21, 2014

Fun with WSJT-X

Since this weekend's ARRL 100th Convention, I've been trying out WSJT-X, the latest from Joe Taylor K1JT in his series of "Weak Signal" programs.  It supports the JT65 and JT9 digital modes, mainly for HF communications (1.8 - 30 MHz).  It's a more modern and user-friendly program than the original WSJT.

The JT65 mode, shown here as a waterfall spectrogram in the 17 M band, is Joe's classic mode.  It uses 64 tones plus a pilot to convey the digital message in a ~200 Hz band.  This selection is interesting, because the weak WSJT-X signal (JA1VGV) is hidden behind a strong RTTY station -- the two big vertical bars.  The JA station is -17 dB relative to the SSB noise level, while the RTTY signal is probably > 0 dB. 

A contact goes in 1 minute "chunks": sending for one minute (actually, 48 sec.) and receiving for one minute.  The divisions of transmit/receive are shown as red horizontal lines. (The waterfall is stopped for 48 sec during transmit.)

I use two power levels for JT65. Normal is 5 Watts.  When conditions are tough, I can ramp up to "QRO" -- 20 Watts.  To go higher than that is considered unsporting, I think!

JT65 is nice, but JT9 is better.  It uses the same message structure, but with only 9 tones that are spaced more closely.  JT9 is much more efficient in terms of spectrum utilization (by a factor of ~10), so it is clearly a better solution for crowded HF bands.  Unfortunately, most of the JT65 software now in use does not support JT9.  WSJT-X supports both.

Sunday, July 20, 2014

ARRL 100: Report from Hartford


The first 100 years of Amateur Radio (and the American Radio Relay League - ARRL) is now history. The National Centennial Convention closed that chapter yesterday in Hartford CT. The second chapter is slowly opening.

The League put on a great conference in the Connecticut Convention Center; a fine venue in an interesting city. If you hiked around the newly developed riverfront, you would come to the the Old State House and a lively street scene. Great food and music!

There is an occupational hazard in ham radio and the ARRL. We sometimes focus too much on how we got here – our 100 year history – and not so much on where we are going. A lot of us are old-timers with nostalgic thoughts about how we got into the hobby long ago, our first rigs, the controversies along the way, "Rotten QRM" and so on.

Conference presentations did try to look ahead. Craig Fugate KK4INZ, FEMA Administrator, gave a compelling view of Amateur Radio as a vital backup emergency service "when all else fails". The challenge is to go back to the future – to be sure you can communicate when the public telephone and data networks are completely off-line. High technology comm. systems have proven to be surprisingly brittle, just when you need them most. It was amazing to receive that kind of endorsement, personal and professional, from a high place in government.

Joe Taylor K1JT gave another keynote talk that was billed as future-oriented. Joe is a friend who is well-known as the driving force behind the WSJT weak signal communications software, a physicist and astronomer, a regular guy, and, yes, a Nobel Laureate. Even K1JT's "futures" talk was heavily biographical and historical, describing a moving personal journey that brought the audience to its feet.

Both Fugate and Taylor were given well-deserved ARRL Medals of Honor.

Futures? I found the forum talk by Frank Lloyd AA7BQ to be the most challenging. Frank is the guy behind QRZ.com, the well known callsign database and forum site. From humble beginnings redistributing the early FCC tape-based callsign data, QRZ has grown into a leading edge cloud-based Internet service, with a staff of 4 or 5 people. The site claims to be the number one Amateur Radio web site.

QRZ.com's basic service is free, but it has a number of subscription services at prices $20 per year and up. The latest is an on-line logbook service and accompanying award program. The front-end website for logging and log analysis looks quite appealing. I expect it will be a serious competitor with other on-line services like LoTW and eQSL.

What might that mean for ARRL's future? ARRL still needs to continue to reinvent itself for the Internet era. Increasingly, ARRL's identity will (and should) be as an Internet service provider – in addition to the traditional member service, technical, and regulatory roles. The League does have its big website (with lots of good content, but lots of problems, and only a weak forum system) and the LoTW program. LoTW is widely considered to be security-heavy and user-unfriendly, aimed at qualifying for ARRL awards, but having little "social media" orientation. All that said, it does serve an important role!

http://www.arrl.org/arrl-second-century-campaign
One of the problems for ARRL is finding a new revenue model to support an aggressive Internet program. The $39 dues are amazingly low, given all the services that are supported not to mention QST. Many hams are happy to pay another $39 or more to QRZ.com or similar services. That should be sending a message to the League.

Transitioning to digital publications is hard for any print publisher, but it is necessary. Digital QST is a first step, but it still has too many limitations that come from the print world. Where is Digital QEX – and other kinds of digital newsletters or forums on special topics?

That's the big challenge. The League has to stay relevant on the Internet! Oh, and on the bands, too. :-)


Friday, June 13, 2014

IPV6 ready

Comcast has blessed me with a working IPv6 connection, viz http://test-ipv6.com/:



What does it mean?  It means that we're all set when some of the Internet service providers are forced to use the new IPv6 addresses when there are really no IPv4 addresses left. (That's likely to begin soon.) It also means I'm behind the curve technically.  I understand IPv4, more or less, but v6 seems very different and a lot more complicated.

Comcast also upgraded us to 100 Mb/s download (from 50) without fanfare.  That's nice, but I'd rather have had a 50% price cut.

Wednesday, May 14, 2014

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.

Sunday, April 27, 2014

Internet Speed Tests

At AA6E, we are using the Comcast "Xfinity" "blast" service, which originally provided 50 Mb/s download, but now seems to have been quietly upgraded to ~100 Mb/s. Oh, we seem to have IPv6 service now, too.  Effectively using that in my home network will be a challenge. (One that I don't need at this time!)

Test with http://speedtest.comcast.net (MA server):


but Boston is not 5300 miles away!

Comcast (NJ Server):


Broadband Reports offers a more sober report http://www.dslreports.com/ (NJ):


The list price for this service is pretty steep IMO ($60/mo), but a slower service is not much cheaper.

Thursday, March 06, 2014

Nice things from Getty Images

Getty Images has a new program that lets you use some of their large supply of professional images for free for nonprofit purposes.  It's called their "Embed Images" service.  It's less flexible than you might want.  You can scale the image, but apparently can't crop it. You have to use their embedded viewer. (They give you an "iframe" to insert in your HTML.)

Still, there are possibilities.

Can I embed in a blog post? Let's give it a try:

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