Monthly Archives: December 2008

More Hardcore Homebrew — Cutting Quartz Crystals

Yesterday’s linked article about negative resistance oscillators got me thinking about the possibility of creating a radio where literally every component was made by hand. Okay, I’m not quite ready to make my own wire, but the zinc oxide oscillator that Nyle Steiner seemed like it was only one step away from reaching a reasonable approximation to that goal: instead of a transistor, it used an oxidized strip of zinc. Making potentiometers and capacitors isn’t that hard: the book Voice of the Crystal will give you some ideas about those.

The one element that seems like a specialized, manufactured bit of kit is the quartz crystal. But I suspected that even this could be manufactured, I just didn’t know where to look for information. But then I rembered that my ARRL membership included access to historical back issues of the QST magazine archive, going back to the time of World War I. Sure enough, a short search later uncovered a pair of articles from 1935 by Ivan Loucks, W9ON. Sadly, I can’t reproduce links to the articles here (they are copyrighted), but the first is from the Jan, 1935 QST, and is entitled Cutting Quartz Crystal Plates and the second from February is entitled Grinding and Finishing Quartz Crystal Plates. Combined, the two articles give a pretty good description of how quartz crystals can be cut from raw quartz, dimensioned and then ground and polished into crystals suitable for making oscillators.

This information opens up the possibility that you could make a radio transmitter with no premade components. I think that’s pretty interesting.

Addendum: Here is a history of the development of quartz crystal technology. It pointed me at an additional pair of articles about crystal control by J. Herbert Hollister from 1928 and 1930 in QST. From the article Quartz Crystal Facts, Hollister opens with this:

With just a year of the narrowband era behind us, we find the ranks of the quartz crystal exponents growing daily. At this time last year most of us thought crystal control was only some trick arrangement for the other fellow to play with and squander his money on. There were few, however, who did not envy the crystal controlled station with the beautiful bell-like note which was always to be found at exactly the same point on the dial.

Zinc Negative Resistance 80 Meter CW Transmitter.

The Spark, Bang, Buzz website has a lot of really interesting low cost electronics experiments involving homebrewing electronics components. Like making your own vacuum tubes, cathode ray tubes, and negative resistance devices. The last is very cool: using a heat treated piece of zinc, you can make a simple oscillator which was documented in the following youtube video. I’m gonna have to try this sometime.


httpv://www.youtube.com/watch?v=uLYQgrFPB3k

The transmitter sounds a bit chirpy, but check out the schematic! It’s pretty darned simple, it’s hard not to accept a little chirp.

Santa Mark and Elf Scrappy

Carmen got a cute little elf hat for Scrappy. He didn’t scratch or fuss too much, but neither was he especially happy. We decided to get a quick picture of him, and then gave him a little cat treat and let him get rid of his elf hat.

On Serving Web Pages…

I must admit, I’ve been running WordPress for quite some time, and for the most part, I’m pretty happy with it as weblogs go. But there are a couple of things that bug me about it. For one thing, it isn’t really very simple. In fact, it’s not just that it isn’t simple, it’s that it’s complexity seems far outpaced by its utility. Allow me to explain: WordPress requires the installation of a bunch of fairly complicated software. It needs Apache (I have heard of it running with other webservers, but such a configuration isn’t well supported in my experience), PHP and MySQL. While the default installation is okay for modest blog installations like my own, to be able to support a decent load, there is the need to use caching plugins, perhaps offloading static content onto a different webserver, and generally a lot of performance tuning.

For instance, here is the output for running “siege”, which simulates a 15 simultaneous users trying to access my blog:


Transactions: 54 hits
Availability: 100.00 %
Elapsed time: 10.86 secs
Data transferred: 2.06 MB
Response time: 2.15 secs
Transaction rate: 4.97 trans/sec
Throughput: 0.19 MB/sec
Concurrency: 10.68
Successful transactions: 54
Failed transactions: 0
Longest transaction: 5.36
Shortest transaction: 1.53

10.68 transactions per second seem like it might be okay, but it’s no where near saturating the link speed. On the other hand, if you are serving mostly static content, you can use a server like thttpd. Here’s the output of a similar siege session simulating 200 simulatenous users:


Transactions: 4249 hits
Availability: 100.00 %
Elapsed time: 10.62 secs
Data transferred: 13.21 MB
Response time: 0.01 secs
Transaction rate: 400.09 trans/sec
Throughput: 1.24 MB/sec
Concurrency: 2.41
Successful transactions: 4249
Failed transactions: 0
Longest transaction: 0.27
Shortest transaction: 0.00

It’s running flat out: each page actually loads two files, so we get 400 transactions per second. The thttpd server haul’s major ass.

Okay, yes. The WordPress blog is running all sorts of dynamic code, but 99% of the time, it’s producing precisely the same static content. We aren’t really getting a huge payoff for our huge decrease in available throughput. We could serve literally hundreds of simultaneous users with even modest hardware if we made better use of static content.

It seems to me that there could be a nice weblogging system based upon this rather simple observation.

Google Code University

One of the greatest things about computing technology is simply how much information is available to anyone who is interested. Technical reports, papers, and most importantly, open source software tools are all available to whomever wants them. This represents a significant democratization of technology. Major universities like MIT are even making entire college level courses available to the public.

It’s nice to see that Google is trying to do the same by establishing the Google Code University. Lots of good information available here.

Google Code University – Google Code

This website provides tutorials and sample course content so CS students and educators can learn more about current computing technologies and paradigms. In particular, this content is Creative Commons licensed which makes it easy for CS educators to use in their own classes.

The Courses section contains tutorials, lecture slides, and problem sets for a variety of topic areas:

  • AJAX Programming
  • Algorithms
  • Distributed Systems
  • Web Security
  • Languages