Monthly Archives: October 2009

DC40B Construction: Day 3

Toroids. Today it was winding toroids. I really don’t mind winding ’em, it is stripping and tinning the leads that seems to be annoying. Nevertheless, I got the four toroids done (two simple, one bifilar transformer and one regular) and installed on the board. A simple continuity check between the pads indicates that all is well.

Should be really easy to finish the radio this weekend, just need to install the transistors, ics, a couple of electrolytic caps, and then power/speaker leads.

Midway DXpedition, courtesy of my HW-8

Well, as I was heading off to bed, I was reminded that there is currently a DXpedition operating from Midway island using the callsign K4M. A quick google revealed that they were operating on 7.078 SSB, so before heading off to bed, I decided to power on my HW-8 (ever since I got it, the FT-817 has been side lined) and see if I could hear anything. And, voila, here is K4M responding to G0HNW (in England). I just grabbed a small snippet of audio, but it gives you some ideas as to what you can hear with a radio like the HW-8.

K4M answering G0HNW on 7.078 SSB, October 15, 2009 07:05 UTC

Addendum:

Same recording, but with noise reduction courtesy of Audacity

Addendum2: I was wondering what algorithm Audacity actually implemented for noise gating. It’s spectral noise gating. I had previously blogged that papers by James Moorer provided some details of similar algorithms, but it appears that my previous links to him had decayed, so there is a fresher one.

DC40B construction: Day 2

Well, I found a replacement for the one resistor I screwed up, and started work on all the caps. They are all in and double checked (I only screwed up one capacitor, which I quickly desoldered, moved, and resoldered). I then got the trimmers in, and soldered in the 16 pin socket. I was gonna start on the toroids, but Mythbusters was on, so I thought I’d take a break. I’m guessing it will take a couple more sessions to get all the semiconductors in, do some minimal testing, and then apply power for real.

Stay tuned….

DC40B construction underway…

DXxxB3Well, after playing around with my Heathkit HW-8, I was struck by a feeling of productivity and started working on my latest kit, a DC40B from Hendricks’ QRP Kits. It’s a very cute little rig, consisting of a 1 watt (ish) transmitter with a built in Atmel AVR keyer, and a direct conversion receiver. It’s crystal controlled, and this one will be built on the crystal frequency of 7.040 Mhz.

Tonight, I started soldering in all the resistors, the diodes, the one molded inductor, and the two eight pin sockets. I noted a couple of issues with the instructions. First, it says that R5 is a 2.2K ohm resistor, but that it’s code should be BROWN-BLACK-RED (which is actually the code for a 1K ohm resistor). I worked around the instructions, and figured that it probably should be a 2.2K resistor and that the listed color code was wrong. I’ll double check with the schematic when I have a chance. In the process though, I managed to goof and install one resistor in the wrong place. Hence, I need another 2.2k ohm, and I couldn’t find one in my junk box. Oh well, a trip to Radio Shack or Fry’s should make that happen if I can’t scrounge the right one together. It also says there should be a 16 pin socket (which reading the Yahoo! help group, nobody seems to get). I could solder it in place, or get a socket.

I did make two mistakes (I mixed a RED-RED-RED with a RED-RED-ORANGE, and mixed a resistor with a similarly marked molded inductor which was truly stupid), but some snips, soldering braid and the like, and I’m back on track.

I might try my hand at winding some of the toroids tonight, and tomorrow: all the caps will go in. Then, it should be a short walk to a working radio!

I’ll keep ya posted.

PROPNOMICON: From the Mountains of Madness

Shifting gears a little from my normal subject matter, I’ll confess to a certain literary guilty pleasure: I like the writings of H. P. Lovecraft. I’m not saying they are the highest literature: I just find them to be an interesting style, creating a mythos that I find a compelling backdrop for a collection of creepy stories. I also like things like fossils and the like (I keep an Elrathi kingii on my desk). So, I find the following craft project strangely compelling: to create Lovecraft-themed props.

Gads. Next, I’ll be making steampunk stuff…

PROPNOMICON: From the Mountains of Madness

My new toy, a Heathkit HW-8

Yesterday I managed to be the winning bidder for this little radio at the QRP Pacificon. Mike Schettler, WA6MER was kind enough to put it up, and I thank him profusely, it’s a very nice little rig. Now, I am one step closer to emulating Bill, M0HBR, as I have BOTH a Drake 2B and a Heathkit HW-8. Heh.

Addendum: My apologies for saying the word “actually” three times in once sentence. Chalk it up to me being fairly excited.


httpv://www.youtube.com/watch?v=A4fCK9VPC0U

Kurt Akeley’s Publications

The other day I was lucky enough to be invited by Bob Whitehill to share a lunch up at UCB with Marty Banks, Kurt Akeley and a bunch of other vision researchers from their lab. I was lucky enough once to have been interviewed by Kurt when he was at SGI back in 1994 or so. His office faced Moffett Field, and on that particular day, they were test flying Harriers. My recollection was that we spent time mostly discussing a program that he wrote in OpenGL to emulate the barrel distortion of fisheye lenses, and watching the Harriers go back and forth. I didn’t get the job offer, and Kurt had no recollection of it. Oh well. I suppose I remember that day pretty well because after my SGI interview, I went directly to a first date with the terrific lady who would later agree to marry me. October 25th, 1994.

Since I’ve been living in the bowels of Pixar production, I must admit that I haven’t been keeping up with Kurt’s doings, and it seems like that is a big mistake on my part. In trying to look up a paper that he co-authored with Marty et. al on stereo displays, I found his page at Microsoft which links to a lot of interesting material.

Archived for future digestion.

Kurt Akeley – Microsoft Research

LCROSS to impact the moon…

This Friday the NASA LCROSS probe will deliberately impact in a dark crater on the moon, with the ultimate goal of trying to decide if any water exists on the moon in these deep craters. As it happens, I was going to take Friday off from work anyway, so being awake at 4:35AM Pacific Time isn’t beyond the realm of possibility. I’m currently surveying my existing telescope equipment (most of which hasn’t been out for quite some time) and hope to be able to video the resulting impact. Regardless, I’m planning on being awake to see it. Check out the NASA website:

NASA – LCROSS

BROADCAST YOUR PODCAST

Well, this isn’t quite amateur radio in the sense of ham radio, but it’s a cute and potentially useful project: a simple fm transmitter that uses only a single transistor, and is built “Manhattan style” on a scrap of PC board. If you’ve been looking for an excuse to try Manhattan construction, this might be a fun, low risk project that requires only the most minimal of investments.

BROADCAST YOUR PODCAST.

More on the Softrock Experience…

I am not really that much closer to figuring out why opposite sideband rejection is so poor, but I downloaded a couple of different SDR programs in the hopes that they might provide some diagnostic which might point more at the exact cause. Rocky still seems to be the best. PowerSDR seemed to work and has many cool features, but also seemed to pop and glitch occasionally. I also tried KGKSDR, which is a nifty program too, but which gave a glitch or two as well. I think the take away from all this is that sound cards suck.

But, a couple of interesting milestones with this: I decoded my first SSB signal with it yesterday (nifty!) and also my first PSK31 signal (Rocky has a built in decoder).

Oh, and I spent some time looking for a new scope. No luck yet.

My Softrock 40…

So, I’ve had my Softrock 40 on the shelf for a while. When I’ve hooked it up, I don’t get very good opposite sideband cancellation. I think I see why, although I’m not sure how to proceed to fix it.

First of all, check out awesome WB5RVZ page on the Softrock Lite. The basic idea is that the Softrock runs an oscillator at 4x the center of the receive frequency (at least for the 40m version, the 30m is a bit different). The oscillator in the 40m I’ve got runs at 28.224 Mhz. It then runs two separate divider chains that create two (essentially) square waves run at 7.056 Mhz (which becomes the center frequency of the band received). Each of these is mixed with the incoming signal, and the result summed back together, which should result in an image of the entire band (subject to Nyquist sampling restrictions, naturally).

But what I’m seeing in my reciever is that I’m seeing each frequency at the opposite side of the carrier frequency (if I am trying to see a signal at 7.070 Mhz (say, a BPSK frequency), I also see the same signal on the opposite sideband at 7.042 Mhz.

It’s not hard to see why. I recorded a bunch of audio from it on my laptop, and plotted each sample as an X-Y pair. Have a peek:

Screen shot 2009-10-03 at 9.40.07 PM

If the radio were working properly, I’d expect to see a very symmetric pattern here, but instead we see an ellipse at 45 degrees. Not good. The thing is, I’m not sure what could be going on here. I’ve hooked an oscilloscope to the divider outputs, and seem to get what I would expect (although my scope is only a 20Mhz one, and the waveforms seem a bit distorted, which could be the scope or the radio). It seems unlikely that the two divider outputs could be that far out of whack: it’s just a set of cmos dividers. My best guess is the sloppy job I may have done on the trifilar inductor that I wound as a mixer. What do you all think?

I’ll try to get some oscilloscope screenshots up here later. i am still a rookie at using the oscilloscope, and haven’t been able to get the X-Y pattern that I expect yet.

Addendum: Here’s an example showing the lack of opposite sideband cancellation. I recorded some audio and ran it through my own spectrum rendering code, each horizontal pixel is about 20ms. You can see that the power in each sideband isn’t exactly even, but that we can clearly see the same signals on both sides of the middle frequency.

opposite

Addendum2: Here’s a photo of the X-Y of the two quadrature channels. I’m somewhat confused actually about the scaling: I am getting significantly more vertical deflection than horizontal, but that result seems to hold even when I reverse the channels. That obviously can’t be right. I probably have my scope configured in some stupid way. Oh well, this is how we learn, right?

IMG_0066

Addendum3: Yep, something is definitely wacky. Here we are in dual trace mode. You can see the amplitudes are very close to the same, although the shapes aren’t very pretty.
IMG_0067

Addendum4: AK6L sent me this link, which shows what I think the waveforms should look like…



cpu_from_scratch [bradthx.net projects]

Every few months, I read about some one who embarks and completes a homebrew CPU project. A few months have gone by, and here’s another. Someday, I really, really, really am going to have to do this myself.

Recently I decided to take on a very ambitious project to design my own microprocessor from scratch. A couple of things inspired me on this project, the first being a book I finished, Digital Apollo by David A. Mindell. This book details the design and engineering behind the AGC (Apollo guidance computer) and I was amazed to learn how well designed both the hardware and software were for it's time. The fact that it was designed completely with 3-input nor gates made it even more amazing. The second reason is the fact that several other people have done the exact same thing, built entire computers from basic TTL logic. A few blog posts have been floating around the internet detailing other peoples CPU designs, looking at these I knew it was something I could easily do myself and would be a very fun project.

via cpu_from_scratch [bradthx.net projects].