A Christmas Present from Argentina

There is an old saying in Spanish:  "No hay mal que por bien no venga."   More or less this is the same idea as: "Every dark cloud has a silver lining."  Well, the dark cloud was my techno-agony with the parasitic oscillations (see below).  The silver lining was the e-mail from Edgardo, LU1AR, in Buenos Aires that helped me get rid of them.    Edgardo advised putting a resistor across the primaries of the JBOT amplifier stages.  This is an old "lower the Q" trick, the idea being that lowering the Q might help prevent the amp from self-oscillating.     I used 680 ohm resistors.   First I put one across the primary of Q1.  No joy. Then Q2.  No luck.  Then I put one right across the primary of that big output transformer.  That did it!  The parasitics disappeared.   And I still get a nice 4 watts of output.  Thanks Edgardo.  I hope to make a contact with this rig today. 

The real silver lining in this story comes, however, in the form of Edgardo's blog site.  Wow, what an inspiring example of Argentinian Knack.  Radios, telescopes, auto-giros.  This guy is also into homebrew DSB rigs.  Wonderful stuff.  Check it out.  (Google will translate it for you, if necessary, but even if you don't read Spanish, the pictures tell most of the story.) 
http://www.lu1ar.blogspot.com.ar/
Thanks to all who sent advice and encouragement.  Merry Christmas! 

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Woe is me! Why Podcast is Late: Parasitic Oscillations!

I'm building my FOURTH JBOT and this one is giving me more trouble than all the others combined.  
Here are the details of my tale of woe:
20 meter rig.  Double Sideband.   The JBOT is fed by a simple two-diode, trifilar toroid singly balanced modulator.  NO DIPLEXER TO SPEAK OF.  At the output of the balanced modulator there is a 1000 uH choke to ground and a .001 uF cap to the input of the JBOT.  AF amp is an LM-386.  VXO is a very simple MPF-102 one stage ceramic resonator VXO with no buffer stage.  7 element low pass filter (three coils, four caps). 
All the transformers are wound on FT-37-43 cores.  T3 is four such cores stacked 2X2.
 
The arrangement works beautifully into a 50 ohm dummy load.  But as soon as I connect it to an antenna (a dipole out in the yard, fed with 50 ohm coax) the output signal gets ugly.  
Looking at it on the scope, instead of the nice figure eight pattern (similar to the two tone test pattern of SSB) I get ugly fuzzy outcroppings from the peaks.  Looking at the signal more closely I can see that in addition to the 14.2 Mhz signal, there is another LF oscillation at around 250 kHz. 
I've been struggling with this.  I can't get rid of the LF oscillations. The leads are all short and the inputs are far from the outputs.   I've beefed up shielding, and decoupling.  I've sacrificed a chicken to Papa Legba. Nothing seems to help.  
I THINK the feedback/oscillation is taking place in the JBOT itself -- not through the
audio amp or the balanced modulator or the VXO.
I watch the RF and the AF inputs to the balanced modulator to see if there is any difference between the stable situation (with the 50 ohm dummy load) and the unstable situation (with the antenna),  I don't see any differences. 
I even put an antenna tuner between the final and the antenna anb made sure that the antenna looks like 50 ohms non reactive.  This seems to help a bit, but the ugly instability is still there. 
Help me! 
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LadyAda Named Entrepreneur of 2012

Watch this video and you will see that Limor Fried has The Knack!
She and her company have brought homebrew electronics back to lower Manhattan.
Some kind listener sent me a gift certificate for Ada Fruit.  We will put it to good use, probably
with Raspberry Pi and Arduino gear.
Three cheers for Lady Ada!

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Roadkill Violins! LandfillHarmonic

Landfill Harmonic film teaser from Landfill Harmonic on Vimeo.

Wow, this is a really inspiring video about being inventive, overcoming obstacles, using what you find and putting junk to good use.  I thought you guys would like this (ESPECIALLY ROBERTO!).

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FITSAT-1 Flashing Morse With LEDs from Orbit

Very cool:  Japanese students sent up a small satellite.  One of its capabilities is to flash Morse code messages in the visible light range using LEDs.   Prepare to peg your geek meter: 
http://www.fit.ac.jp/~tanaka/fitsat.shtml 

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PE1JXI's BITX-20 Handheld

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Watching a Light Beam at One Trillion Frames per Second

Billy alerted me to this TED Talk presentation on an MIT Media Labs project that used new "femto photography" techniques that allow us to watch -- in VERY slow motion -- a light beam pass through a bottle. Amazing. Makes me think about Einstein's old thought experiment about running alongside a light wave (but of course here they are slowing down time...)

 Here are some details on how they did this:
 http://web.media.mit.edu/~raskar/trillionfps/ 

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African Knack

Thanks to Allan, WA9IRS, for sending us this inspiring video. Just the right touch for Thanksgiving. This kid is definitely one of us. Let's try to think of ways to help him. Parts box? Radio books?

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

Get SolderSmoke For Christmas! 30% off (23-27 Nov)!

Use the little mail icon (below) to forward this to those who are buying you things for Christmas!   30% off if you buy 

23-27 November.    Here are books: 

http://www.lulu.com/spotlight/soldersmoke

Our book: "SolderSmoke -- Global Adventures in Wireless Electronics" http://soldersmoke.com/book.htm Our coffee mugs, T-Shirts, bumper stickers: http://www.cafepress.com/SolderSmoke Our Book Store: http://astore.amazon.com/contracross-20

NA5N, a Solar Flare, and the Very Large Array

I think I said before that Paul, NA5N, has one of those "dream jobs" for a radio amateur.  Confirmation of this came in a message he posted to QRP-L today: 

We're running a special experiment today using the VLA antennas to observe at 74 MHz (a protected radio astronomy band) and at 327 MHz.  We've hung dipoles just below the antenna subreflectors, acting as a virtual ground, and of course the 88ft dia. dishes to illuminate the dipoles.  Picks up a lot more power from the sky than I would have thought (about 30dB gain over the same dipoles in free space). 
Anyway, about 0830 MST, suddenly the system temperature climbed about 200 deg. K.  Our switched power calibration injected into the LNAs showed no shift, meaning the jump in power came from the sky, not from the electronics.  The power plot looked just like a solar flare.  Checked the NOAA site, and sure enough, we had an M4 solar flare from region 1618 ... about smack in the center of the sun.  About 1530UTC=0830MST=1030EST, Wed. Nov. 21. 
NOAA has since measured the shock wave from the CME at 1918 km/sec.  This is a fairly strong shock wave, and coming from the center of the sun means planet earth will be pretty close to the bulls eye. 
The first time in my life I witnessed a major solar flare in real time watching the "sky power" plots.  Pretty neat.  First time the astronomers involved in this experiment have witnessed a solar flare as well real time. 
Region 1618 has produced numerous C- and M-class flares past couple of days with high potentials of future activity.  This will ionize our E/F layer for elevated MUF and weak signal reflection.  Check the bands if you're not at work. 
This 1918 km/sec. shock wave headed for us will almost assuredly trigger a major geomagnetic storm in a couple of days.  If it hits Friday evening, it will trigger likely aurora over northern U.S.  It may hit Saturday.  I'll check the NOAA predictions later today and post as to the expected shock wave arrival. 
72, Paul NA5N
Socorro, NM
Currently inside of VLA antenna #5, west arm.
http://www.vla.nrao.edu/ 

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Another VK3YE DSB Rig

Hi Bill

       A short e-mail from across the pond. Thanks for sharing the VK3YE link, so impressed I was that I have built one. 

It receives great and puts out a nice looking dsb signal, looking forward to some good qso's, ready to improve on it as we speak and looking to make a top band and 18m version also, love the site and keep up the good work...Ian

Ian Miller

G7FFV

UK

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"Road Kill" Batteries for Us?

http://news.nationalgeographic.com/news/energy/2012/11/121116-second-life-for-used-electric-car-batteries/


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