Digital Pot

No, this is not some on-line mail order thing.  Bruce KC1FSZ has done something that I find both amazing and horrifying:  he using a "digital potentiometer"  as the AF gain control in his BITX.  Remember when pots were simple and pure, when they were just a metal wiper that ran across a crescent of carbon of increasing resistance?  Well, those happy days are apparently behind us my friends.   What now?  Will we have endless discussions about where to find the driver for the 10k pot?   Will Facebook or Amazon or Microsoft secretly seize control of the data on our AF gain, perhaps to sell us hearing aids?   But enough of my ludism.  Good going Bruce.  AGC beckons. 

Hi:

I've built a few BITX rigs from scratch now and I'm starting to move to a modular approach using fabricated PCBs to make it easier/faster to build/mix/match the stages.  My audio amplifier module is based on the LM386.  I know others have moved away from this chip, but it still works for me.

I've added one feature to my audio amp stage that opens up some good possibilities.  Instead of the traditional potentiometer between the AF preamp and the LM386, I've inserted a digital potentiometer (MCP4131-103) that is controlled by three extra pins on the microcontroller.  The digital pot lists for $0.81 on Mouser so it's no more expensive than a physical pot and it's way more versatile.

Why do this?

• The module is quick to make if you're building a lot of rigs.
• AF gain can be controlled via the CAT port.
• AGC control can be done in software.  This enables all kinds of fancy AGC "attack" and "release" controls that can be seen in the docs for commercial rigs.
• This is an enabling feature for remote ops, which is why I did this in the first place.
• AF gain can be controlled using the same encoder (different mode) as is used to control frequency, etc. if you wanted to build a more compact rig.

The board is shown below.  This is one of my first forays into KiCAD/PCBs/etc. so it's probably not as "tight" as it could be.  Also, I'm using through-hole components so it's old-school building.  But the board only costs $7 on OSHPark and it's pretty quick to wire up.  Anyone who wants to order one from them drop me a line and I'll send you the link.

Schematic below.

73s,
Bruce KC1FSZ

Peter's New Airplane

Again.  Amazing.  What a great workshop.   Note his comments on the importance of DESIGNING FIRST, THEN BUILDING.  Words to live by my friends, words to live by.  Read and heed.  

Video on PCB Factory in China

This factory is a LONG way from Manhattan -- both from the island and from the technique.  

How about some Juliano Blue PC Boards?   

The machine that automatically checks for bad connections was especially amazing. 

And the boards are made in 24 hours, with 3 day shipping to the U.S. 

"First Man" Neil Armstrong Movie Trailer

I think Ryan Gosling is a good choice to play Neil Armstrong.  It looks like this movie will deal with the "right stuff," a concept somewhat related to "the knack." 

Another Wood Box BITX! KC1FSZ Abandons Al-Fresco but Continues with Wood

'Tis a thing of beauty.   I like the wood.  And I like the hood.  The handles are a nice touch.  A fitting follow-up to its al fresco organic origins.  

Hi Guys:

I know there was a view that my giant BITX was supposed to be left out in the open, but I’m going to try to attend my local club’s Field Day festivities this year and the 4 foot long “planker” was pressing the limits of portability.  So I moved from the shack to the wood shop and built myself some custom cabinetry.  I think it looks a bit like an IC-73000 now don’t you think?  OK, maybe not.  

There is a hinged door at the top and shelf levels inside for the different parts of the circuit. The power supply and PA section are mounted on the bottom which can be removed for accessibility/serviceability.   The whole thing weighs about 10 pounds!!

73s,

Bruce KC1FSZ

Understanding Antenna Directivity -- Help from Canada

I am in the process of repairing my beloved 17 meter fishing-pole Moxon.  It was taken out of service by the last Nor'easter of the winter.  This repair has caused me to review the theory behind antenna directivity.  I find there is a lot of "hand waving" in the explanations of how directivity happens:  "You put a reflector element next to the antenna.  And it REFLECTS!"   You are left wondering how that reflection happens.  

The Royal Canadian Air Force made a video that does a pretty good job of explaining how the reflector reflects.  See above.  Thanks Canada!  

While we are talking about antennas,  I wanted to alert readers to a really nice antenna modeling program that is available for free.  It is called 4nec2.  You can find it here: 
http://www.qsl.net/4nec2/   There is a bit of a learning curve, and I am still climbing it, but I can see how this software would be very useful.  It has an optimization feature that runs the antenna through many versions and tells you how to optimize for F/B,  gain,  SWR, or whatever you want to prioritize.  

I have discovered that my Moxon was resonant below the 17 meter band.  In other words, the antenna elements were too big.  About 3.6% too big according to my calculations.  This may be the result of my using insulated wire for the antenna elements.  Apparently the MOXGEN software assumes the use of uninsulated wire.  I'm thinking that an easy way to deal with this would be to use the frequency 3.6% above my target frequency and then use the dimensions given my the MOXGEN program.  Any thoughts on this plan? 

What a shame that Cebik's web sites have all disappeared.      

INTERVIEW: Bob Crane Talks to Jack Purdum W8TEE at FDIM. Definition of "Homebrew."

Jack Purdum has been making enormous contributions to the radio art.  His background with digital technology has opened many doors for homebrewers, especially through his books on the use of the Arduino microcontroller.   I think his new "JackAl board" is really going to shake things up.  I was glad that our correspondent in Ohio, Bob Crane W8SX, caught up with Jack and interviewed him for soldersmoke: 

http://soldersmoke.com/W8TEE.mp3

But I have one small disagreement with Jack.   It has to do with the definition of "homebrew."   Jack seems to define true homebrew as "designing and building your own rig from scratch."  My problem is with the "designing" part.  By this definition, those intrepid heroes of days-gone- by who saw a schematic in QST, ripped apart some old broadcast radios, and used the parts to build a 50 watt CW transmitter with a regen receiver were not true homebrewers.   I would maintain that they were.  I agree with Jack that kit building is a bit different, and of course designing the rig yourself earns you the coveted "designer" designation.  But for me, if you start with a schematic and an article, gather the parts and build the thing yourself, that is a homebrew project and you are a homebrewer.  After all, even the designers are very often making use of standard blocks of circuitry (Colpitts oscillators,  common emitter amplifiers, power supply circuits, etc.)

I think we will have to turn to our lexicon expert Steve Silverman for a ruling.  

In any case, thanks to Bob Crane and to Jack Purdum. 

Hans Summers and his QCX -- G0UPL Cracks the Code on Si5351A Quadrature

Pete,  Brad WA8WDQ and I were recently e-mailing about our admiration for what Hans G0UPL has achieved with his QCX rig.   I cc'd Hans -- we got this nice and very informative e-mail.  Be sure to click on the link provided by Hans, and from there go to the link to his FDIM proceedings article.  I think that article is a real masterpiece -- there is a lot of very valuable information in there.  For a long time, getting quadrature output from the Si5351 seemed like an impossible dream.  But Hans has obviously figured out how to do this, opening the door to much better and simpler single-signal phasing receivers.   Thanks Hans!  


Hi all

Thanks for the nice feedback on the QCX and the FDIM conference proceedings a article, which I have published on QRP Labs web page along with other Dayton trip miscellany. See

 http://qrp-labs.com/dayton2018.html

My seminar presentation audio was recorded by Ham Radio Workbench podcast and they will be publishing it on 5th June.

The QCX kit has indeed been unbelievably popular, almost 5,000 kits have been sold since the launch on 21st August. It seems to have itched an itch that needed itching, in the QRP world. Sales continue to be strong and I'm currently preparing another batch of 1000 more. 

I'm very proud of my 90-degree quadrature Si5351A and it helped me towards my low cost, high performance target for QCX. Abandoning the 74AC74 saves a part, reduces cost, reduces complexity, reduces board area (and hence more cost) and even seems to provide better performance (higher unwanted sideband rejection when using the Si5351A in quadrature mode). Getting the Si5351A to do this is one of those things which look easy afterwards. But at the time, and faced with SiLabs un-useful documentation, it took an awful lot of headscratching, trial and error!

I'm not sure of the answer to the question about noise figure. Certainly radios such as QCX and the NC2030 which use the QSD architecture seem to have very high sensitivity without an RF amplifier ahead of them. This must indicate a low noise figure. 

73 Hans G0UPL 

http://qrp-labs.com 

VK2BLQ's Beautiful uBITX in a Wooden Box

Now that, my friends, is a BEAUTIFUL uBITX.  Stephen VK2BLQ put that one together.  Peter VK2TPM helped him get the KD8CEC software into his Raduino (Stephen had trouble  getting it to compile on his Raspberry Pi).  

For me there is good news and bad news here.  The bad news is that I can no longer tell people that mine is the only "wooden box" rig that they will ever work.   The good news is that I am no longer alone. 

INTERVIEW: Four Days in May 2018 -- G0UPL Hans Summers talks to Bob Crane

Once again, our correspondent Bob Crane W8SX has gone to the Four Days in May event and has sent back some really great inteviews with those who made presentations there.  

First on the list was Hans Summers G0UPL.   Hans is a justifiably famous Homebrew Hero, and a member of the QRP Hall of Fame.   The latest of his many contributions to the hobby is his amazing QCX transceiver.  Like the BITX rigs, the QCX refutes the idea that hams need to spend kilobucks to get on the air with a decent rig.  Priced at around $50,  the QCX offers excellent performance.  And it comes with built in test gear:  the signal generator you need to align the rig COMES IN THE RIG!  FB Hans.  

I think it was Pete who noted that the price range for rigs like the QCX, the BITX, and the uBITX is in the $50 to $110 dollar range, meaning that "One hundred bucks is the new three thousand bucks."  We owe a lot gratitude to Hans and Farhan for this very positive paradigm shift. 

Listen here for Bob Crane's 2018 FDIM interview with Hans: 

http://soldersmoke.com/G0UPL-18.mp3

We all also owe a debt of gratitude to the QRP ARCI folks who did all the hard work that goes into organizing Four Days in May.  Special thanks to QRP ARCI Preston Douglas WJ2V, and to FDIM Chair Norm Schklar WA4ZXV.  FDIM is one of the most important events on the Homebrew/QRP calendar. 

More info on the QCX (and order yours) here:  https://qrp-labs.com/qcx.html

An Epic Evening on 40 Meters

I had a good night on 40 meters last night.   The Radio Gods were obviously with me.  

First I called CQ and VP2EIH on Anguilla responded.  Nice to start with a whiff of DX.  

Then Jason W5IPA called in and said he wanted to try out his uBITX! See the pictures below.  FB!  

Then I got a call from K5WDW on Hilton Head Island -- Dexter runs Collins gear from an ocean-front shack (see above).  Check out his QRZ page.  

Then WA4PUB called in.  Dave has been on the air since 1948 and was a student of legendary ham and radio astronomer John Kraus.  Dave has directional antennas on 40 -- when he switched the pattern he went from LOUD to barely detectable.  FB.  Check out Dave's homebrew rig below. 

Finally Gary W7DO joined us.  He has a big 4 Square on 40 that also has some really impressive directional properties.  See below for a look at his 80 meter 4 Square. 

TRGH

WA$PUB

W7DO 80 meter 4 Square

BITX Night on 7277: First N6ORS and then Canadian BITX Builders

 I was about an hour late for the Eastern time zone meet-up at 7 pm local on 7277 kHz Sunday night (my wife and I watch 60 Minutes at that hour). but I figured I could work some guys if I got on at 8 pm.  Sure enough, I was called by Keith N6ORS on his MIN-X rig.  I was on my QRO DIGI-TIA.  It was great to catch up with Keith. 

Then I got a call from VE3THR.  Last year I'd talked to Tom when he was using his BITX40.  This time he was on with his uBITX.  FB.   Tom's club in Barrie, Ontario is obviously melting a lot of solder and having a lot of fun.  Here are some pictures of their rigs.