BITX Build Updat #4 VFO Stability

I wasn't quite satisfied with the long-term stability of my VFO.  It seemed like it was drifting about 70 Hz per hour, even after the initial warm-up period.   So, all out of Q-Dope, I went to the local pharmacy in search of clear nail-polish.  (My family was making fun of me.)   I got home and applied several coats of "Sally Hansen No Chip Top Coat Vernis de Protection."   I let it dry a bit, then started watching the frequency counter.  At first results were disappointing.   Drift continued.  Now it seemed to be drifting up!   I cracked the books.  EMRFD has a good chapter on temperature compensation of VFOs, but the process seemed painful.    I wasn't looking forward to it.

I left the VFO on when I went to work, noting the freq as I departed.   Ten hours later I returned, and was delighted to find the frequency almost exactly where I left it!  It may have taken a while for the nail polish to completely dry.    I'll leave it running again today to see how it does.


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BITX Build Update #3

This weekend I built the VFO.   I used Doug DeMaw's FET Hartley, from his "QRP Notebook," page 50.

Getting a VFO into the desired frequency range always seems to involve a bit of "cut and try."  Not only do you have to get in the correct freq range, but you also have to try to get the tuning range of your variable cap (or coil) to match the band you want to cover.  In my case, thinking of 20 meter SSB, I need about 200 kHz of tuning range.  And sticking with my 9 MHz (for 20) and 13 MHz (for 17) plug-in filter plan, I need the VFO to be in the 5 MHz range. 

That main tuning cap you see above has more capacitance than necessary (19-148 pf).  One option would be to pluck out some of the rotor plates (been there, done that).  But that seems a bit barbaric, so instead I just reduced the overall capacitance by putting a smaller fixed capacitor (about 20 pf)  in series.      

Yesterday I had it percolating nicely.  Waveform looks beautiful on the Tek 465.   But it was drifting too much.  I had a cheap plastic trimmer cap in there.  This morning I replaced it with a more substantial ceramic trimmer.  This seems to have improved stability quite a bit.

I need to put some stabilizing substance on that toroid.   DeMaw prescribes Q-dope.  I'm all out.  What is the field expedient substitute?   Was it clear nail polish? 

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BITX Build: Update #2

Not much progress to report.  But I have been thinking about the filter frequency.  Here is my latest idea: 

Maybe I'll build the VFO in the 5 MHz range.  This would allow me to use the 9 MHz Yaesu filter (and associated crystals) that Steve Smith sent to me (see above).  With this I could be on 75 and 20 meters. 

I could build another filter at 13 MHz and, using the same VFO in the 5 Mhz range, get on our beloved 17 meter band.  I kind of like the idea of plug-in filters. 

You can see my ideas for the board layout.  I'm thinking of a Doug DeMaw Universal Hartley VFO inside the box shown above.   The tuning cap you see is out of an old Heath QF-1 Q Multiplier.  It has a very nice reduction drive built into the tuning shaft.  It measures 19 to 148 pf.     
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Building the BITX! Update #1

There it is guys:  A blank canvas of copper-clad board.  A clean slate ready to be filled with the components for a BITX transceiver.  As you can see, I am fighting my "build first, design/plan later" tendencies.  No real design work for me on this one (thanks Farhan!) but I am trying to plan where everything will go on the board.  (Thanks to Jim, W8NSA for the board.)   I'm going to build it Manhattan style (perhaps with an ugly dead bug or two).  I'm starting with a big board because I always seemed to end up with a shortage of space.  It looks like I can easily get all of the circuit (minus the PA) on this board.  I'll build the PA on a separate piece of copper-clad.

I'd like to build it for 17 meters, but if I stick with the 10 MHz filter that means I have to build a VFO at around 8.1 MHz.  That's not impossible, but in my experience it is easier to build simple, stable VFOs at lower frequencies. 

 

I notice that there are a lot of cheap crystals available at higher frequencies.  So, instead of keeping the filter at 10 MHz and trying to get the VFO stable at 8.1, what do you guys think about keeping the VFO in the 4 MHz range and  building the filter with crystals in the 14 MHz range? 

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

Pete Juliano's KWM-4

 

Pete Juliano, N6QW, has authorized me to provide SS Daily News readers with a look at his magnificent KWM-4, a solid state version of the legendary Collins transceiver.  This project is in the Summer edition of QRP Quarterly.  Amazing job Pete! 

 

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

A COOL Norwegian "S" Meter (video)

Immaterials: Light painting WiFi from Timo on Vimeo.

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

Peter Parker's Video on SP5AHT's Phasing Receiver

There are so many very cool aspects of this project:  I love the phasing receiver arrangement -- it uses the same basic concept that allows my old HT-37 to generate SSB (I struggled to understand it as a kid, and finally succeeded!).   The use of the mobile phone as an audio spectrum analyzer is wonderful.  The N3ZI signal generator looks a lot like the DDS project I was working on (I should have bought N3ZI's! ).  I've been seeing these square pattern PC boards in many projects lately -- I may try this in my next project.  And of course, it is very cool to see a circuit designed in Poland being put to use by a fellow radio amateur in Australia -- a good example of the International Brotherhood of Electronic Wizards!

Here is the page for the SP5AHT rig that inspired Peter:

http://www.sp-qrp.pl/modules.php?name=Content&pa=showpage&pid=54

It is in Polish, but Google should translate it, and, in any case, we all speak Schematic!

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

"Chart of Electromagnetic Radiations"

Wow, all you need to know, right here on one poster!  They even cover particle/wave duality.  I tried printing it up in hi-res but the uncertainty principle seems to be interfering! Get yours here:  http://www.flickr.com/photos/llnl/9403051123/sizes/l/ 


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

Oscillo-porn! A $500,000 Oscilloscope! (video)

I don't know,  I think I like my Tek 465 better!  But if any of you guys are thinking of buying one of these, PLEASE do so via the Amazon link on my web page!

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

Dipoles in Space! Millions of them!

http://www.wired.com/wiredscience/2013/08/project-west-ford/

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

SolderSmoke Podcast #154

SolderSmoke Podcast 154 is available for download!

http://soldersmoke.com/soldersmoke154.mp3

August 11, 2013

-- Alligators!  Real Alligators! (see picture below -- look closely)

-- Ten meter beacon project (with Arduino and Reverse Beacon Network)

-- Telescope repair:  Chap Stick as lubricant, and the perils of macular pucker!
 
-- HW-101 saved from cannibalism!
 
-- The Wonders of WSPR and our need for instant feedback and gratification.

-- QST Review of SolderSmoke, The Book.
 
-- MAILBAG

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

Kishan Has the Knack! (video)

Many of us were staring out similar windows, also dreaming of model airplanes, and of transmitter circuits, and telescopes, and rockets... This video runs only 12 minutes.  Don't be deterred if you don't speak Hindi -- the story is easy to follow.

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