I posted a message on qrp-l just recently regarding selecting the right operating frequency for colpitts oscillators. In the schematic you'll notice the connection between a pair of series capacitors. I had wondered if possibly this was behaving as a voltage divider. One member of the list, Nick Kennedy, had an interesting explanation for how it works. With his permission, I am repeating his post here:
I think the capacitors are a voltage divider, sort of, but a voltage adder too. Depends on where you're standing.
Let's say for example that the caps have a reactance of -100 ohms apiece. The total would be -200 ohms, so the inductor would also have 200 ohms reactance at the resonant frequency. The circuit is driven by the voltage across source resistor in parallel with the lower capacitor. Looking at that element (-100 ohm capacitor) in isolation, it is in parallel with 200 - 100 ohms or 100 ohms inductive, so it is driving a parallel resonant circuit.
The resulting circulating current of course creates twice the drop across the 200 ohm inductor as across the single -100 ohm capacitor. And the voltage across the other capacitor is the same and in phase, so the two voltages are additive. The voltage at the gate is twice that across the lower capacitor. So looking at the two capacitors separately, we have a divider but looking from gate to ground, and adder.
You can do the though experiment with unequal caps too, say 70 ohms and 30 ohms. You still find the source resistor driving a parallel resonant circuit and a greater voltage from gate to ground than across either of the two caps.
"I think Mengele’s case highlights how the idealised image of the objective Academic, struggling only to further knowledge, can be a road straight to hell."
A quote from this post on the Phineas Gage Fan Club blog. It's a grand post, I highly recommend reading it. The author considers Mengele as model of villainy and evil. There is an interesting thought here. Mengele wasn't one-dimensional. He was not pure evil, although he did some terribly evil things. Many speak of him having a playful side. Hitler, I have read, was very cordial in person and had a great sense of humour. The holocaust is an example in many ways of pronounced faults in human psychology that we must all be personally aware of and careful about. The author in the aforementioned post mentions the danger of logic without controls. Logic is a tool. It is an extremely valuable tool, but if it is not regulated by morality and ethics it can lead in bad directions.
We can see this when we consider the behaviour of individuals in the Enron scandal, or even spammers. The behaviour they took part in is to a person in their position completely logical and reasonable. This is evaluating the situation without the benefit of ethics. Pure logic can be very destructive without an ethical framework within which it can be contained.
The Phineas Gage Fan Club blog has just put a post up on audiophiles and the limitations on hearing. It has a good discussion of why many people will believe the bunk presented by subjective reviews. Another point mentioned by the author, that I have not previously elaborated upon, is differences in hearing abilities. We know, for example, that sensitivity to high frequency audio drops off as a person ages. This rate is not constant, and varies by individual. It is also extremely common for people to have greater sensitivity to all sound in one ear or the other. I've never heard of audiophiles taking hearing tests to determine these characteristics of their own hearing, then tuning the system in a compensatory fashion. All audiophile review sites, in my opinion, should post a profile of the reviewer's own hearing sensitivity. Only by doing so is it possible for the reader to insure that he experiences the same response from the system.
It is possible to claim that perhaps I am going overboard on this. There is a lot of money involved in this realm, and people should be able to make informed decisions on what they buy. I am in no way condemning the ultimate goal of the audiophile - that is, the pursuit of high-quality audio reproduction for personal enjoyment. I listen to a lot of music(mostly bluegrass and old time, oddly enough), and music brings a great deal of joy into my life. The pursuit of a well-built and designed stereo system is a worthy and interesting one. The problem is that if we are to accept audio cables worth $7,000, and audio amplifiers worth $20,000, it behooves us to be very careful in our evaluation of the claims made about these products.
Extraordinary Claims Require Extraordinary Proof
That truism is a profoundly unpopular one. It means work, hard work. Physicists and chemists and mathematicians and other scientists spend their entire lives satisfying this maxim. It is because of the demand for proof and logical reasoning that we have computers today. We have better steel, better food, better water, better concrete, better everything than ever before. It is said that the steel in the hull of the Titanic was of such poor quality that today it would not even be used in rebar. We have achieved miracles and forged the impossible through persistence and ingenuity. Why should I not ask the same of stereo systems? Is it unreasonable to demand of audio the same methodology that has served us so well in other fields? The demand for real numbers, for real science, exists not to diminish the field. It exists to expand the field. The goal is to shed the husk of mythology and smelt out the scummy dross of subjective measurement, so that only the pure truth may remain. We are on a hunt for gold, and only methodical and careful refinement can extract it.
Of course, if we just declare pyrite to be gold we can go home early and get drunk. Decisions, decisions...
I was talking with a friend recently about atmel AVR chips. Specifically, he was looking at the ATtiny44. This part has 4kB of flash, but it has two sister components with 2k and 8k as well. These are the ATtiny24 and the ATtiny84, respectively. My leaning is towards the higher flash, just because I'm lazy and like bootloaders:) I decided to do some investigation on price to see where these chips are sitting. I use Digi-Key's canada site, being in canada it's more convenient for me. The ATtiny24 sells for $2.06, the ATtiny44 sells for $2.32, and the ATtiny84 sells for $3.13. That first 2k is worth 26cents, the final 4k is worth 81 cents. On a per kilobyte basis, the 4k in the '84 is almost twice as expensive as the 4k on the '44.
This just came in over email from EDN, the 2007 microprocessor directory. With Microchip and Atmel out there, and Renesas, Rabbit, NXP, etc. it's hard to know just what's available. EDN has rounded them all up on one site for your perusal. It's quite a list, the PDF version is about 130 pages.
Nota bene: This is substantially a rant about people being stupid.
The results are in from the Radiohead 'experiment'. In spite of it being available online for people to pay what they wished, it was still distributed significantly on filesharing networks. Here's the thing that gets me. After all this time, they still don't get it. One pundit says:
"If the community rejects even forward-thinking experiments like this one, real harm is done to the next generation of experimentation and change,"
Good grief! There are 13 year old teeny boppers on myspace who get it. There are people who don't know what an operating system is, who get it. I am going to point out something that, in spite of it being blaringly obvious to many of us online, still seems to have eluded the minds of the few. The internet is for moving and processing information. Music is information. What will the internet do with it? Move it and process it. People participate in this because they are using the internet for what it's best at. Seriously, there are little kids who understand this. But the music industry doesn't. Musicians: Your music will always be on filesharing networks. You won't get it off. You can't get it off. I know this can be frustrating, people are doing things you don't want them to do with your creation. All I can offer as solace is the reality that if it's on the network, that means people like it. They enjoy it. Filesharing networks are systems built on popularity. What this means for you is that your name is out there and you can actually sell your music. It is far worse to not be on the network at all, than to be all over it. My advice is to accept it, find ways to use it to your advantage. At the very least, you have created something that has brought a great deal of joy into peoples lives.
I still haven't got the aforementioned image running on my emulator yet, but I have managed to get myself an account on a public system running ITS. Now that I'm using ITS I'm beginning to see the code of RMS in a new light. See, he was a big ITS hacker back in the day. You can see the influence in his code. info, emacs, and hurd all have that feeling. As you use ITS, it starts to make a lot more sense.
I'm not sure how many of you have heard of ITS. It stands for the Incompatible Timeshare System. This was developed at MIT, by hackers, for hackers. Before UNIX, it was the preferred OS of the hacker. The quirk with ITS is that it has no security. None whatsoever. Usernames exist only for the convenience of being able to identify each other. In many ways, Wikipedia is application of these principles. Stark proof that signal can, in fact, outpace noise.
I have been of late hunting high and low for a usable ITS image. I found a distribution that is far more complete than the one I had been using, but everyone linked to ftp.its.os.org for it. That site is now down, and it looked like the image had never been mirrored. Astoundingly, this is where the FreeBSD ports tree comes in. One pdp10 emulator of note is klh10. This was ported to FreeBSD, and entered in to the ports tree. Somewhere along the line, the maintainer(Turing bless him) included the image along with the port sources! This is, to date, the only place I have been able to find with a mirror of the file. I plan in short order to organize hosting, so there is perhaps more than one place hosting it now.