SolderSmoke Podcast 166: Getting Started in Homebrew Radio

SolderSmoke Podcast 166 is available for download: 

http://soldersmoke.com/soldersmoke166.mp3 

Bench Report:  Pete working on Direct Conversion Receivers.  
Bill on his 2B and on 20DSB rig, and an M0XPD/Kanga DDS kit, and a 140 watt amp. 

GETTING STARTED IN HOMEBREW:
Start simple:  Build an oscillator. Make it oscillate!
Gather tools, simple test gear, and books. 
Try to understand what you build. 
Build a direct conversion receiver.  
Don't fear the toroids! 
Be patient.  This is not Plug and Play. 
Build a DSB transceiver. 
Little tips: 
Protect variable caps. 
Use heat sinks. 
Use reverse polarity protection. 
Don't breathe the solder smoke! Ventilate your bench.

China Radio International Mystery Solved.  
Book Recommendation:  "International QRP Collection" by Dobbs and Telenius-Lowe
MAILBAG

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Sines, Squares, Harmonics, 'Scopes, FFTs, and Sounds

Bil Herd of Hackaday did a very nice video on Sine Waves, Square Waves and FFTs.  This is, of course, an important part of understanding how mixers mix.   I look forward to his upcoming video on Direct Digital Synthesis.  

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Hunting for Sprites

Don't let the comments about "positive lightning" and "gravity wave" cameras turn you off -- in the world of meteorology, these terms seem to make sense (but I had to do some Googling).  The New York Times article on this topic is very interesting: 

http://www.nytimes.com/2014/09/30/science/on-the-hunt-for-a-sprite-on-a-midsummers-night.html?_r=0  

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Beautiful Pictures of Mars from India's Spacecraft

Congratulations to the Indian Space Research Organization.  They put a spacecraft into Mars orbit on their first attempt, and they are getting back some spectacular images.  

I also like the banner on their web site: 

More info here: 

http://www.isro.org/pslv-c25/Imagegallery/mom-images.aspx

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

Don't miss Thomas and his Minima at Pacificon!

Thanks for the kind words Thomas.  Be sure to have someone do a video of your presentation.

You truly have The Knack -- proof of this is your reaction to your wife's departure for field research in Senegal:  "IT'S SOLDER TIME!"  That's the spirit! 

Too bad about the chickens, but hey, they died for a good cause... 


Dear Bill,

I have been listening to your podcast for about a year now. I think you were right to say that one episode a month is a reasonable limit to avoid listeners getting addicted. At some point in January I was listening to you every morning and every evening in my car, a very serious case of addiction.

This is also the time that Farhan chose to announce the Minima and my wife to go to Senegal for 3 months for a field study (she is doing a PhD in Sociology). I think it took me less than a week to run to the shop, get most of the parts and start melting solder!

In two weeks from today I will present the project and my build at Pacificon. I would really appreciate if you could mention this on your blog because I am sure there are other listeners who will be there and curious for some homebrewing-materials. I hope to delight them!

For your own pleasure there are some pictures and videos on my blog: http://www.sarfata.org/ham/minima/ 

Pacificon Schedule:  http://pacificon.org/ (My talk will be at 10:45 in the Portland room)

My presentation will retrace my journey building the minima. From the first smokes on the crystal filter when I was not even sure how to test it, or what results to look for ; to the amplifier where I am still battling some oscillations (by the way, if you had not talked so much about them, I would never have understood what was going on!).

This project has taught me that radio is a lot less black magic than I thought. It bridged the gap between the maths that I can understand but not really "see" and the sound coming out of the amplifier. It made me realize that once split into stages, a radio is much better understood and testable. Without a doubt, this has been my most ham-enriching experience and I hope to convince more people to build a minima, preferably Manhattan style! 

(In this public setting, I will probably not discuss killing chickens to exorcize my amplifier but I thank you for the tip ...)

I got pulled back from homebrewing by life and work this summer but I kept the last three episodes of Soldersmoke on my phone. They were my safety parachute and I listened to them last week on the way home to give me the extra boost that gets me to melt solder or fix bugs until 3 in the morning on a tuesday. I don't think I will ever be able to express my gratitude for all that I have learnt reading the book and listening to you but I would like to start here: Thank you!

Please keep the podcast going! I have really enjoyed the new format with Pete. 

73,
thomas
kk6aht / f4hdq


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Let's Build Something! (Video) Part 1

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Radio China International Echo Mystery SOLVED!

For the past month or so I have been wondering about a strange echo that I've been hearing on the 31 meter transmissions of Radio China International.  I first noticed it on my "Kings Speech" regen receiver.  Then I heard it again on my "Off the Shelf" regen.  

For a while I thought that what I was hearing was a propagation effect:  Perhaps the very strong RCI relay station in Quivican,Cuba was sending north a signal so strong that it was travelling around the earth along the grey line and coming back to me about .133 seconds after the original reception.  

This sounded plausible (and it does happen sometimes).  But there were reasons for skepticism: Why wasn't anyone else hearing this?  Why wasn't the effect showing up on signals from Radio Havana Cuba?  

Pete Juliano had suggested that perhaps I was getting signals from TWO different RCI transmitters.  I had quickly checked the RCI schedule and didn't see them transmitting on the same frequency at the same time from multiple transmitters, so I kind of put that idea aside.  Hey, the round-the-world idea was just more appealing! 

But then I remembered something strange about the echo:  It seemed to disappear when I tuned close to the center frequency of the RCI signal, but then appeared when I tuned off to one side. Hmm.... That was an important clue. 

I've long been wary of regen receivers and for a while suspected that I was dealing with some weird regen effect.  Regen and Echo seem to go together, right?    Well, as it turns out, no.  But I was right about this being an effect of the nature of my receiver... 

Last night I was listening to RCI English service at around 0030 UTC on 9570 kHz.  Nice clear signal.  No echo. 

At 0100 UTC the program changed, and the echo started.  A very strong echo. 

I went to the RCI schedule.  Here I found the answer: 

At 0030 they were transmitting from their relay station in Cerrik, Albania on 9570 kHz. 
At 0010 they switched programs, frequencies and transmitters.  At 0100 Cerrik shut down, but the Quivican, Cuba relay came on on 9580 kHz.   At the same time the RCI transmitter in Kasi Sabagh in far-off exotic Western China, in Xinjiang, fired up on 9535 kHz.  Both transmitters were carrying the RCI English service. 

You see, my little regens are not very selective, and the RCI transmissions are quite strong.  So if I have my receiver tuned to around 9560 kHz, I'll be hearing BOTH the signal from Cuba AND the signal from Xinjiang.  That would explain the echo. 

To try to confirm this, last night I fired up my old Hammarlund HQ-100 receiver to see if I could discern the two different signals.  I could.  And the echo appeared when I tuned BETWEEN the two.  You can hear this in the video above. 

There is one remaining question here:  Is the echo caused by the RADIO path difference between the two transmitters?   Or are we just seeing the effect of the programming being transmitted at slightly different times, perhaps with this delay caused by INTERNET latency?  Anyone know how RCI gets its signals from its Beijing studio to its distant transmitters?   I calculate that the path difference is about 10,000 km.  With c at 300,000 km/second, that would yield an echo of only about .03 seconds.  The echo we are hearing sounds longer than that, so I suspect we are hearing a difference in studio-transmitter transmission time.  What say the SWL RF gurus?

BTW:  I think the same phenomenon may explain the echo on Brother Stair's "Overcomer" signal.  I see that starting at 2200 UTC he is on BOTH 7570 kHz and 7730 kHz from RMI transmitters in Florida.  Perhaps they are not synched up. 

I think this is all very cool.  Think about it:   Here I am, sitting in Virginia in 2014, listening to the Albanian, Cuban, and Xinjiang relay stations of Radio China International on a receiver first built by some guy in England during the 1930s.  And I'm trying to figure out if the echo I hear is caused by the limits imposed by the speed of light and the size of the earth,  or by the time it takes packets to move through sub-oceanic fiber optic cables.   

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

Making Hardware for Mars in a Lab in New York City

I liked this video about building hardware for a Mars mission at a lab in New York City.

http://www.sciencefriday.com/video/08/10/2012/building-for-mars-sometimes-painful-always-glorious.html


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

The Amazing Apollo Board from Carbon Origins

Wow, lots of possibilities here....

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Arduino Makes Music with Old Floppy Drives

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A Beautiful BITX20 from PA1ED

Edwin did a beautiful job on his BITX.  This is an excellent example of stage-by-stage construction. 
This is his THIRD BITX.  On the second one he got all the parts from an old television and a washing machine.  That's the true BITX spirit!  
I want an S Meter!  
There is more information on his blog:
http://pa1ed.blogspot.nl/

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

The SWLing Post, Ears To Our World, and the HumanaLight

Thomas, K4SWL, has a really impressive shortwave listening blog.  Yesterday he was kind enough to post an article about my latest obsession:  the echoes on China Radio International: 
http://swling.com/blog/ 

Even more impressive is Thomas's work on behalf of poor people in the Third World. He is the Director of Ears to Our World, a charity group that provides innovative, simple and appropriate technologies to schools and communities in remote, rural and impoverished regions of our world.
Here they are: http://www.earstoourworld.org/

They distribute radios to people who would no other regular technological contact with the rest of the world.  They are also involved in an intriguing project called the HumanaLight:  "Dead" AA batteries power lights that can make a big difference for people living in areas that have never been on any grid.   Here it is: http://www.earstoourworld.org/humanalight/

Ears to Our World is looking for Donations to help them bring light and radios to people who really need them:   Here is where you can help: 
http://www.earstoourworld.org/donate

This is clearly a very appropriate charity for radio amateurs. 

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