brainwagon "There is much pleasure in useless knowledge." — Bertrand Russell

31Jan/090

Overnight WSPR spots on 40m

I got home fairly late last night, and wasn't up to any serious radio activities, but I did activate my WSPR beacon on 40m, and let it run. This morning, around 8:00AM local time, I was treated to a pretty good haul of DX spots especially from VK4 land. I had spots from VK4ZW, VK4YEH, and VK4ZBV, as well as ZL3IN and 7L4IOU. I think it's about time for me to make up a new spot map.

I'm shifting the beacon over to 30m, then it's time to prepare goodies for the superbowl party at Sandy's tomorrow.

Addendum: Shifted over to 30m, and managed to get VK6DI from Western Australia. Awesome, I think that's a new personal distance record. Yep, that's about 700 miles farther than my previous record via 9V1LF.

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30Jan/090

It once was lost, but now is found…

This morning as I was heading out the door, I scanned my bookshelves for something that I could read during my lunchbreak. Much to my astonishment, I saw this book:

ssdra

Yes, that's right: a copy of Wes Hayward and Doug Demaw's classic Solid State Design for the Radio Amateur. I'd been looking for this thing for months without any luck, but it turns out my wife had seen it lying around the house and had done what you are supposed to do: put it back on the shelf.

There has been a lot of discussion about SSDRA on the QRP-L mailing lists: used copies go for astoundingly irrational quantities of money (in excess of $200). While I think this is absurd, I do the book is very good, and I like it even better than its touted replacement Experimental Methods in RF Design. I can't wait to dig into it some more.

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29Jan/091

A Stereo Picture

Here's the gang I work with at Pixar Animation. This was taken with the incredibly low budget technique of snapping a picture, moving the camera, and snapping another one. Of course, a couple of us moved in the interim, but thanks to the judicious work of Reid, who carefully stitched and offset various bits, it works remarkably well.

group

29Jan/091

On the politics of clubs..

Steve has an interesting post entitled "Golden Rule and Imagined Worlds" on his blog. It's an interesting post, suggesting that transparency and equality are the basis for a good club.

I'm not sure I disagree, but I am going to take a different tactic, and it will be of the following form: how much "organization' does your club really need?

Imagine that you loved ham radio a whole lot, and found two or three others that really did too. Because you all like it, it's natural to want to dedicate time to pursue it, and to share your interests with like minded fellows. So, perhaps you decide that you can go to a local pancake house on a particular day and talk about radios. Surely nobody here has any power over any body else: you are expected to pay for your own pancakes, and if you don't like the conversation any more, you stop showing up. There is no need for a "president" or a "secretary". If someone wants to (say) put up a synopsis of the discussion on the web so that others can see what you talked about, well, then they can do that. If you don't want that to be your job, then don't do it: nobody is forcing you. If they aren't discussing what you like to talk about, then find some others who do, and go to lunch with them.

But from these simple beginnings, things get more complicated because people think that if they just pooled their money, they could do something interesting. They could build a club station, or a repeater, or even buy up old rigs, fix them, and give them to new hams. If it's just a couple of people, they usually just make an agreement, and do it. But if it gets to be a reasonably large number of people, they might disagree upon what exactly the priorities should be for their donated money. So, they decide to elect a leader, whose thankless job is to try to intuit what they really should be doing. Maybe that works okay, until the group grows a little bit more. Then, the total amount of money gets larger, and it's too big of a responsibility for just one person. So, you start electing a board, and keep minutes, and draft bylaws and...

Hey, weren't we supposed to be doing radio stuff? Why is our copy of Solid State Design for the Radio Amateur getting dusty, while our Robert's Rules of Order are getting dog-eared?

Any club that doesn't spend 99% of its time actually doing the thing they were formed to do is no club I want to participate in. The more money you contribute, the more bureaucracy is needed to manage it. Here's an idea: keep your money, and keep your amateur radio activities something you do with friends. If they try to assert power over you, just laugh, and hang out with someone else. Spend your time doing stuff, rather than discussing stuff.

Filed under: Amateur Radio 1 Comment
28Jan/091

Bill’s ET-1 / FETer (Transceiver Made with One FET)

Bill is building an FETer (Transceiver Made with One FET) as published in Sprat by G3XBM. I don't get Sprat (but should), but you can get the design off this web page. A very simple, truly minimal design. It's like a haiku constructed from solder. I have some MPF102s in my junkbox. I might just have to give it a try.

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27Jan/090

TEMPEST: A Signal Problem – Hack a Day

I'm not 100% obsessed (more like 98%) with radio topics: this morning, I found this link on Hack a Day which provided a link to several articles having to do with TEMPEST. I've blogged about TEMPEST before, but for those who haven't heard of it before, it's a way of eavesdropping on electronic signals by listening for insecure, electronic emissions. I'd seen some of these before, but I hadn't seen this work on evesdropping on USB keyboard emissions:


Compromising Electromagnetic Emanations of Keyboards Experiment 2/2 from Martin Vuagnoux on Vimeo.

I also hadn't seen TEMPEST: A Signal Problem, a paper recently released under the FOI detailing the history of TEMPEST. Very interesting.

24Jan/091

New Japanese Satellite — PRISM

Got a quick recording of the PRISM satellite, launched on the 23rd, as it came over my location. It was booming in, very fast Doppler. Here's a recording and a quick spectrum of it, click on the image to get the spectrum of the 2 minute mp3 recording.

prism

MP3 of the Japanese PRISM satellite on 437.250

24Jan/090

More ngspice experimentation: a harmonic filter

Goofing around while watching Battlestar Galactica (which incidently is one of the most depressing, soul-less, unfun thing to watch that I can imagine) and decided to look up George Dobbs' QRP harmonic lowpass filter design, and see if I could get it to analyze using ngspice. I picked his design for 30m, and created the following ngspice model:


* low pass filter for 30m
VIN 1 0 ac 1 sin
C1 1 0 270pf
L2 1 2 1.09uH
C3 2 0 560pf
L3 2 3 1.257uH
C5 3 0 560pf
L6 3 4 1.09uH
C7 4 0 270pf
Rload 4 0 50
.ac lin 40 10000000 12000000
.plot ac 10*log10(v(4))
.end

Here's the output, plotted on a logarithmic scale:

filt

Seems like it works pretty well, although the peak is actually just above the 30m band.

Addendum: Ah. The vertical axis isn't correct, since I used the log instead of the log10 function. The overall shape is correct, but the scales are off. I updated the code above, and I'll redo the graph in the morning using the appropriate labels. It might also be fun to screw up my amplifier design a bit by introducing clipping, and then combining it with this filter and see how it cleans up the waveform.

Addendum2: Here's the updated filter response, charted over a much larger frequency range. This harmonic filter would be very effective.

filt1

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23Jan/090

QRP Transmitter Design

Here's a nifty PDF on QRP transmitter design. It looks like it might have been cribbed from one of Doug Demaw's books (which you should buy if you are interested in this stuff), but it's just a few pages long, and is quite practical. I think I'm actually getting to the point where I understand what's going on here.

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23Jan/091

Common emitter amplifier design using ngspice…

Okay, I've been reading some of my variou sources on amplifier design including EMFRD and the ARRL Handbook, and decided to try to test my understanding of them by coding up a simple common emitter amplifier, and then testing the model by plotting out the voltages using ngspice, the open source version of the popular Spice code that runs on my linux box. Normally, you'd use a schematic editor to create the circuit, then compile it to a net that spice can read. But for simple circuits like this (and by looking at the examples on All About Circuits, I didn't find it hard to just type in the model by hand. I don't have too much time to go into the details, but here is the code:


# a common emitter amplifier design by Mark, K6HX
# mostly as a tutorial for using ngspice
vin 1 0 dc 3
vsig 2 1 sin(0 .316 10140000)
vcc 3 0 dc 13.8
r1 3 4 27350
r2 4 0 2650
Cin 4 2 10uf
Q1 5 4 6 mod1
Rc 3 5 1780
Re 6 0 220
Cout 5 7 10UF
Rload 7 0 5MEGA
.model mod1 npn
.tran 0.004u 0.12u
.plot tran v(2,1) v(7)
.end

The signal is a 10Mhz sinusoid (I'm eventually interested in making a 30m beacon). The vin voltage source is a dc offset, which basically gets stripped by the Cin capacitor. The signal is then biased by the resistive divider formed by R1 and R2, and then fed as the base voltage into Q1. The gain is approximately -Rc/Re, in this case very close to approximately -8. The voltage is measured across a 5Mohm resistor (modelling the internal impedence of a meter, I just picked 5M ohms at random, mine is closer to 9.18Mohm).

Anyway, here is the plot of the input signal (the smaller amplitude) and the inverted output signal.

amp

I'm learning a lot.

Addendum: Here's the schematic, drawn with a sharpie on a napkin:

amp1

Filed under: Amateur Radio 1 Comment
22Jan/090

Klunky Schematic Drawing

screenshotNeed to make a quick and dirty schematic drawing? Try the Klunky Schematic Drawing page.

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22Jan/090

Six Oscar Nominations for Wall-E!

This morning I awoke to find that Pixar's Wall-E had been nominated for an incredible six Academy Awards!

  • Best Animated Feature Film of the Year
  • Achievement in Music Written for Motion Pictures (Original Score)
  • Achievement in Music Written for Motion Pictures (Original Song)
  • Achievement in Sound Editing
  • Achievement in Sound Mixing
  • Original Screenplay

Pixar's short film Presto also got a nod in the Best Animated Short Film Category.

21Jan/091

All About Circuits on Feedback

lemons2I was digging around information on common emitter amplifier design, and encountered this link which seemed quite helpful. Digging around the All About Circuits webpage, which seems to be a very useful online reference. It helped me understand the presentation that I've been reading in my copy of Hands-On Radio Experiments. More on that soon.

Addendum: My wife just told me that she originally read the title of this blog entry as All about Citrus, and wondered why I would be writing about lemons and oranges. Heh. She should get some sleep.

20Jan/091

From the Inaugural Address of William Howard Taft

I don't speak about politics on this blog very often. Frankly, I don't find politics itself to be very interesing: it is a sphere of human discourse that I find all too obsessed with appearance over substance, and expediency over justice. While this might form the basis of a faintly amusing reality TV show, it's not at all funny when you realize that your rights as an individual are subject to the whims of such forces.

But today is Inauguration Day. President Barack Obama has taken his oath, and is now our 44th President. I think that requires some brief acknowledgement, and this message might serve as a brief letter to my future self regarding what I was feeling on a day where perhaps, just perhaps the nation changed course (hopefully for better).

During the endless news coverage leading up the ceremony, one of the talking heads on the news mentioned that 100 years ago to the day, President Taft asserted during his speech that "Negroes were Americans", and that it was remarkable that 100 years ago, this was not so completely accepted that it required explicit mention. I found that intriguing, and dug out Taft's Inaugural from The Avalon Project:

.The Avalon Project : Inaugural Address of William Howard Taft

I'll quote the part having to do with racial relations, and place some emphasis that I'll explain below::

I look forward with hope to increasing the already good feeling between the South and the other sections of the country. My chief purpose is not to effect a change in the electoral vote of the Southern States. That is a secondary consideration. What I look forward to is an increase in the tolerance of political views of all kinds and their advocacy throughout the South, and the existence of a respectable political opposition in every State; even more than this, to an increased feeling on the part of all the people in the South that this Government is their Government, and that its officers in their states are their officers.

The consideration of this question can not, however, be complete and full without reference to the negro race, its progress and its present condition. The thirteenth amendment secured them freedom; the fourteenth amendment due process of law, protection of property, and the pursuit of happiness; and the fifteenth amendment attempted to secure the negro against any deprivation of the privilege to vote because he was a negro. The thirteenth and fourteenth amendments have been generally enforced and have secured the objects for which they are intended. While the fifteenth amendment has not been generally observed in the past, it ought to be observed, and the tendency of Southern legislation today is toward the enactment of electoral qualifications which shall square with that amendment. Of course, the mere adoption of a constitutional law is only one step in the right direction. It must be fairly and justly enforced as well. In time both will come. Hence it is clear to all that the domination of an ignorant, irresponsible element can be prevented by constitutional laws which shall exclude from voting both negroes and whites not having education or other qualifications thought to be necessary for a proper electorate. The danger of the control of an ignorant electorate has therefore passed. With this change, the interest which many of the Southern white citizens take in the welfare of the negroes has increased. The colored men must base their hope on the results of their own industry, self-restraint, thrift, and business success, as well as upon the aid and comfort and sympathy which they may receive from their white neighbors of the South.

There was a time when Northerners who sympathized with the negro in his necessary struggle for better conditions sought to give him the suffrage as a protection to enforce its exercise against the prevailing sentiment of the South. The movement proved to be a failure. What remains is the fifteenth amendment to the Constitution and the right to have statutes of States specifying qualifications for electors subjected to the test of compliance with that amendment. This is a great protection to the negro. It never will be repealed, and it never ought to be repealed. If it had not passed, it might be difficult now to adopt it; but with it in our fundamental law, the policy of Southern legislation must and will tend to obey it, and so long as the statutes of the States meet the test of this amendment and are not otherwise in conflict with the Constitution and laws of the United States, it is not the disposition or within the province of the Federal Government to interfere with the regulation by Southern States of their domestic affairs. There is in the South a stronger feeling than ever among the intelligent well-to-do, and influential element in favor of the industrial education of the negro and the encouragement of the race to make themselves useful members of the community. The progress which the negro has made in the last fifty years, from slavery, when its statistics are reviewed, is marvelous, and it furnishes every reason to hope that in the next twenty-five years a still greater improvement in his condition as a productive member of society, on the farm, and in the shop, and in other occupations may come.

The negroes are now Americans. Their ancestors came here years ago against their will, and this is their only country and their only flag. They have shown themselves anxious to live for it and to die for it. Encountering the race feeling against them, subjected at times to cruel injustice growing out of it, they may well have our profound sympathy and aid in the struggle they are making. We are charged with the sacred duty of making their path as smooth and easy as we can. Any recognition of their distinguished men, any appointment to office from among their number, is properly taken as an encouragement and an appreciation of their progress, and this just policy should be pursued when suitable occasion offers.

But it may well admit of doubt whether, in the case of any race, an appointment of one of their number to a local office in a community in which the race feeling is so widespread and acute as to interfere with the ease and facility with which the local government business can be done by the appointee is of sufficient benefit by way of encouragement to the race to outweigh the recurrence and increase of race feeling which such an appointment is likely to engender. Therefore the Executive, in recognizing the negro race by appointments, must exercise a careful discretion not thereby to do it more harm than good. On the other hand, we must be careful not to encourage the mere pretense of race feeling manufactured in the interest of individual political ambition.

Personally, I have not the slightest race prejudice or feeling, and recognition of its existence only awakens in my heart a deeper sympathy for those who have to bear it or suffer from it, and I question the wisdom of a policy which is likely to increase it. Meantime, if nothing is done to prevent it, a better feeling between the negroes and the whites in the South will continue to grow, and more and more of the white people will come to realize that the future of the South is to be much benefited by the industrial and intellectual progress of the negro. The exercise of political franchises by those of this race who are intelligent and well to do will be acquiesced in, and the right to vote will be withheld only from the ignorant and irresponsible of both races.

The thing that I found interesting was that even while Taft was asserting that Negroes were Americans, he was asserting the rights of states to create literacy tests (what we now refer to as Jim Crow laws) to keep the "uneducated and uninformed" from participating in elections. Such laws were passed in many states, and were routinely used to prevent blacks from registering to vote. It wasn't until the 1960s that these laws were struck down, by the Voting Rights act of 1965, and by decisions in the Supreme Court like Harper v. Virginia Board of Elections, and South Carolina v. Katzenback. Yesterday, we celebrated Martin Luther King Day, and of course Dr. King was responsible for voter registration drives in Alabama, precisely because of this issue.

As I watched the news coverage, there is one thing that I realized, looking at the images of African-Americans waiting for the inauguration to begin. There is something in their faces that I can understand intellectually, but which I acknowledge I cannot feel, at least with anything approaching their intensity. I voted for Obama because I believe he is a thoughtful man, with good ideas and good ideals. But for many Americans, he's much more than that. He's a symbol of progress.

Here's hoping that he'll be more than symbol, that he'll be an agent of real change.

Good luck, Mr. President.

Filed under: Politics 1 Comment
19Jan/090

A Universal VXO by George Dobbs G3RJV

Well, you can't do better than an article by the legendary George Dobbs, G3RJV. The circuit that he has closely resembles the oscillator that I just built, with a few distinctions.

A Universal VXO by George Dobbs G3RJV

vxo

The general topology is the same, but the resistive voltage divider that feeds the base of the transistor has resistors of 33K and 10K in George's design, while they are a simple 10K/10K in the EMRFD design. In other words, EMRFD biases the transistor with half the supply voltage, while George's design is more like divide by four. George's design says that the capacitive divider should have 100pf capacitors, EMRFD specifies the very high 390pf. The resistor that grounds the emitter is a 2.2k ohm resistor in EMRFD: George specifies a 1K ohm.

Addendum: My oscillator sounded a bit chirpy, and with some additional harmonics, so I began to look up designs for harmonic output filters. Of course, Dobbs has another excellent resource containing worked out designs for all ham bands.

Addendum2: Here's a link to the GQRP clubs technical info page, which is a superset of the information provided in the link above.

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