Clifton Laboratories 7236 Clifton Road  Clifton VA 20124 tel: (703) 830 0368 fax: (703) 830 0711

E-mail: Jack.Smith@cliftonlaboratories.com
 

 

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November 2008 Archives

 

27 November 2008

I've added a discussion from Kenneth Davies's NBS Monograph 80 on ionospheric radio propagation to my Signal Statistics page, as well as signal level data collected at short (100 ms) intervals with a spectrum analyzer. The revision supports my observations that the signal fading I've observed follows Rayleigh statistics, at least for data collected up through 7 MHz. At 15 MHz, WWV's fading statistics look more like Rician fading.

 

26 November 2008

Between the holidays and waiting for printed circuit  board deliveries, I've had a short break.

I received prototype printed circuit boards for my active antenna coupler and a revised active antenna element. The antenna element boards were unusable, as several pads for surface mount transistors were merged into ground. My circuit board vendor will replace them at no charge to me, since it was a manufacturing problem, but I'm unlikely to see the replacements for several weeks. (I'm using SparkFun's prototype service for these boards�double sided boards with solder mask and silk screen on both sides�at $2.50 per square inch. This is a very reasonable price but it's usually a three week turnaround.) The coupler boards�ordered without mask and silk screen from a different source�were usable, although I made a couple of errors and also found it necessary to revise the design in a few respects.

Top view of coupler unit. It has a switchable AM medium wave band reject filter and three isolated, buffered output ports.
Rear view of coupler showing the three buffered output ports, and other inputs.

I'll finish a second revision board layout, close enough to final to justify a solder masked, silk screened PCB in the next few days and order several prototypes.

I'm still trying to find a cost-effective way to label the front and rear panels. Small quantity production of appliqués or silk screening plastic panels results in very high unit costs.
 

18 November 2008

I'm a fan of Neal Stephenson's books, and the last few days have been spent reading his latest, "Anathem."

Stevenson's work defies easy categorization. His classic Cryptonomicon , for example, seamlessly blends World War II codebreaking history with adventure and a touch of science fiction. His three-volume Baroque Cycle (Quicksilver,The Confusion and The System of the World) is a romp through the late 17th and early 18th century, featuring Sir Isaac Newton, John Hooke amongst many others. It's historical fiction, after a fashion, but it's most certainly not historical fiction as you might normally think of it�throw Newton, Hooke, King Charles II, Leibniz, the Countess of Qwghlm and several dozen other dramatis personae into a blender on high speed for two minutes, add a dash of pirates for flavor and serve over ice and you get an idea of Stephenson's ability to mix real and imaginary (Countess of Qwghlm, for example) characters.

Anathem is a departure for Stephenson, as it's closer to classic science fiction than anything he has written since Snow Crash. Anathem is set on an earth-like planet. Arbre, where theoretical science and mathematics is the province of "avouts" who live a life apart from the rest of the technology-using world, populated by the "extramuros" who live in sæcular world. Avouts are "collected" at an early age and live in "maths" or groups of maths,  known as concents. Maths and concents are a blend of university and monastery/convent (co-educational, and "liaisons" between the male and female avouts are permitted). Avouts may leave their maths and visit the sæcular world (and vice-versa) only during the 10 days of Apert. If you are a member of a decenarian math, Apert is once every 10 years; the most restricted are the millenarian maths who recognize Apert only once every 1,000 years.

The sæcular/avout system has existed on Arbre for thousands of years, but has been periodically disrupted when the sæcular world collapses into war, events known as "sacks" by the avout.

The separation between the sæcular world and its government and the avouts is not perfect, and it is possible, on rare occasion to place avouts at the service of the sæcular powers.

In order to avoid spoiling Stephenson's plot, I'll refrain from details, but something never before seen on Arbre occurs that challenges the existence of the planet and its society. A small group of avouts must work with, or at least appear to, the sæcular powers to preserve Arbre and its civilization.

At the core of Anathem is quantum theory and the "many worlds" interpretation of the quantum wavefunction.

Anathem is not going to be to everyone's taste, but I enjoyed it. If you begin reading it, please stay with it�after the first 100 or 150 pages, you begin to realize why Stephenson has started the book the way he did, and when you've finished it, you will understand even better why Arbre seems to be a shadow of Earth.

 

16 November 2008

The "official" statistics from http://marketshare.hitslink.com/report.aspx?sample=25&qprid=32&qpdt=1&qpct=4&qpcustom=Firefox&qptimeframe=D&qpsp=3561&qpnp=31 show Firefox (versions 2 and 3 total) with 20% or so of the browser market.

Visitors to Clifton Laboratories prefer Firefox by a much greater percentage, as reflected in the table below, with statistics for October 2008 visits. Firefox browsers are reported as "Netscape" by my web hosting service. (MS Front Page views are from my updates, as I use Front Page as my HTML editor.)

Firefox users accounted for 41 to 45% of requests during October 2008. Some small percentage of the two Netscape categories may represent old Netscape  browsers, but the overwhelming majority are Firefox.

I've used Firefox for several years�and Thunderbird E-mail�and I highly recommend both.

Pct Requests   Browser
50.14%    MS Internet Explorer
41.02%    Netscape
4.16%    Netscape (compatible)
2.76%    Opera
0.54%    msnbot
0.51%    msnbot-media
0.45%    Googlebot-Image
0.11%    MSFrontPage
0.07%    Yanga WorldSearch Bot v1.1
0.04%    Baiduspider+(+http
0.04%    ia_archiver (+http
0.03%    Mozilla oder so
0.03%    MSR-ISRCCrawler
0.02%    Gigabot
0.02%    SeznamBot
0.02%    Speedy Spider (http
0.02%    ia_archiver
0.01%    User-Agent
0.01%    psbot
0.01%    Yeti

 

 
10 November 2008

I've added two new plots to the Signal Statistics page with fast data collection of a pure ground wave signal, from a non-directional beacon. It shows an almost perfect match with a Gaussian distribution, which is expected for a signal arriving by only one path, groundwave.

 

09 November 2008

I've added two plots to the Signal Statistics page with fast data collection, one amplitude reading every 1.7 seconds. The data shows similar statistical properties with the data collection over longer periods with slower sample intervals.

 

08 November 2008

I've added a new page FM & TV Subcarriers with spectrum analyzer views of FM broadcast and TV aural subcarriers.
 

07 November 2008

I've added a new page Signal Statistics discussing some of my recent skywave and groundwave measurement data. It may help explain why we amateur radio operators see signal fading.

 

02 November 2008

As usual, I've moved the October updates page to archives, viewable by clicking here or through the Archive table link at the top of this page.
 

02 November 2008

I received sample audio transformers from Walters OEP in the United Kingdom in October and have added measurement data to my Non-Linear Transformer page. The OEP8000 transformer is a decent performing device, with lower distortion than many of the other parts I've measured, being nearly as good as the Bourns part.