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Which Greek God are you?

You are the God of war and your symbol is the spear. A good looking man in the prime of your life, you are decisive, determined, and fearless. However, you are also impulsive and quite bloodthirsty, always looking for the next battle to come along. You know what you want and you go straight for it, despite the consequences because you just don't care.
How do you compare?
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But why is the rum gone?!?

LiveJournal Username
Fifteen men on a dead man's chest!
Cutlass or pistol?
What is the name of your pirate ship?
Where is your secret pirate base?
What kind of loot do you prefer?
What do you and your crew prefer to be called?
Parrot or monkey?
Your capable first mateaelman
Your bumbling cabin boy with a heart of goldbattery841
The aloof, yet honorable, pirate with a mysterious pastauroralinux
Is always the first one into the frayscrambledeggs
Is the naval officer who ruthlessly pursues your shiprobey
Is the comical pirate who is always drunk on grogdargus
Is currently in Davy Jones's lockerb_a_t
The amount of money you make as a pirate$164,384
This Fun Quiz created by Lynn at BlogQuiz.Net
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You Are 68% Open Minded

You are a very open minded person, but you're also well grounded.
Tolerant and flexible, you appreciate most lifestyles and viewpoints.
But you also know where you stand firm, and you can draw that line.
You're open to considering every possibility - but in the end, you stand true to yourself.

Oscillators and filters

Since I got my crystals yesterday, I went to campus to see if I could build an oscillator today. Did some looking at my books, and found things that didn't work at all. Did some more searching, tried a few other things, finally came up with a topology and some values that seemed to get me some oscillations. Looked at them a bit on the scope, and the frequency was good to as well as the scope can measure. I'm not sure how I'm going to fine-tune the frequency there, or if I need to. While I was at it, I did find a faster scope in the lab. This one seems to be rated up to 300MHz, and 500MSa/s, which isn't quite good enough to look at my output stages, but it's plenty fast to look at the input.
The output initially looked horrible, lots of zero crossing distortion and other (probably harmonic?) distortions. Putting in a 1uF cap in parallel with a 1nF cap to bypass the power supply helped to clean up the signal quite a bit. Looking at it on the spectrum analyzer, the harmonics seemed quite substantial. After more chatting, came up with the idea of adding a buffer with filtering. Building just a buffer didn't work out at all, so I tried to build a sallen key filter section, using a 2n2222 as the active element. Eventually I got this working well enough to get signal out. Alas, it increased my THD from 24% to 26%. So, the filter section seems to suck. I might try doing a simulation on it, just to see what pspice says it ought to do. Though, after the simulations I tried with the op-amps from TI, maybe that's not such a good idea. I tried building a simple non-inverting amplifier using their models, and the gain always seemed to go kaput right around 8MHz, regardless of which model I used. I'm pretty sure that the signal out of my amplifier is not strong enough to power both mixers, but I'm not sure how I'll amplify it to get it up to the recommended +7dBm (per mixer).
Hopefully those products from TI will ship quickly, and I can start using them as real oscillators. I'm not sure what I should work on for this thing tomorrow.

Almost forgot...

The latest version of my block diagram is available at http://linuxweasel.com/~gleblanc/Detailed%20Diagram%20vMay-04.png

More Progress

So, I made some progress on my project today. Amazingly enough, yesterdays fussing around with filters was not a complete waste. Originally my image rejection filter at my 10.7MHz IF was going to just be a simple first order filter. However, after designing those non-workable filters yesterday, I came up with one that will work just fine at 10.7MHz. That filter is designed and simulated. Looks pretty slick.
My Digikey order came in the mail today. I'll pick it up when I get home. That means tomorrow I need to design my 10.245MHz LO, and maybe even test it. Hopefully that won't be too painful. I've got all of the books here that I should need.
I've decided that I would really like another amplifier at the 10.7MHz IF on the input, just to help get my signal a bit further out of the noise a bit further.
I really need to finish designing my active filter, for my 50kHz bandwidth. I think I've got the right textbook to do that now, so maybe I'll also try to do that tomorrow.

I think that's all for today. I'm off to find out what showing of Spiderman we're going to this evening.

Pre LNA filter

OK, after a bit of looking at Pozar (ISBN 0-471-32282-2), I think I've pretty much come to the conclusion that unless I'm doing this on a circuit board, I can't pull it off. For a 3rd order filter, with cutoffs of 100MHz and 160MHz (which is actually wider than I want, since it doesn't kill off FM radio), I need a capacitor of 5.77pF, which is smaller than I can really expect. For 3db ripple, instead of 0.5dB, it's even worse, though it's not immediately obvious to me why that is. I tried a first order filter, and it got me up to needing a 13pF cap, which still isn't doable. So, I've pretty much given up on doing a filter out in front of the LNA.

Alas, a waste of a whole day of work.


So, I've gotten a comment or two about my journal being just a bit too technical and incomprehensible. When I started on this project, I created some tags thinking that there would be an easy way to filter on the, so that folks could filter in or out things as they chose. However, I haven't seen any way to do that. The only thing that I've seen that's even close is loic's boring computer things LJ feed. But he's created another journal on his website, which I can't do right now, as my web hosting is going away in June, and I haven't secured alternate arrangements yet. Not sure of a good way to solve this that doesn't require too much effort on my part.


Your Vocabulary Score: A-

Congratulations on your multifarious vocabulary!
You must be quite an erudite person.

Senior project PROGRESS!

Ah-ha! Made some progress on my senior project today. I was looking at my diagram, thinking to myself, ok, how do I know if I'm going to have enough gain? Well, what's enough gain? Well, uh, ok, probably just needs to be enough that I've got sufficient signal to mix with, filter, and amplify. I know I've got 20dB of gain from my LNA, so what comes after that? Oh, a mixer, that'll lose me another 6dB. I wonder what signal levels I can mix with. So, I played around with that, and then I realized that for that first mixer, I needed two VHF input frequencies. We've got one signal generator that goes up to 3GHz, but the other one only goes to 80MHz, so that just wasn't going to cut it. I asked if we had any other VHF ones, but we don't. So, I thought to myself, OK, what do I do now? I guess I need to hook up my VCO, and play with that. Soldered some temporary leads to it, got it oscillating, hooked it up to the 'scope. Hmm, this is a 100MHz scope. Well, let's try it anyway. OK, it caps out at 135MHz. Now I have to drag this thing up to the SA, and test it there. It's a little touchy to get it to the exact right frequency, so I'll have to figure out exactly how I'm going to do that on the final board. Maybe a fixed resistor divider, plus a potentiometer in there to fine tune it. Not sure how precise that really needs to be. Check the output signal levels from this thing, they look good, probably close to the +7dBm that my mixer is spec'ed for for the LO. Hooked up the RF generator to the other port, mixed and measured a bit. Looks like I can safely have a signal as low as about -60dBm going into my mixer, and still get adequate output. However, if I want to be able to handle that, I'm going to need an amplifier in the first (10.7MHz) IF stage. I think that's possible, so I'll try to get some gain there.
Talking to some other folks, they suggested adding some filtering immediately before my LNA, to knock out any spurious signals before I amplified them. That's OK, but I'm not sure how to build a filter at 145MHz. More investigation is needed on this. I think I'll break out the electronics book now.