Two Videos from Other Kinds of Workshops -- Dobson Makes a Telescope, Peter Builds an Airplane

Above you can watch a video showing the legendary John Dobson making a big telescope. Born in Beijing, Dobson is the former Hindu monk who left the monastery to show people how to make big telescopes out of shipping tubes and port-hole glass.  Think of it as the BITX of amateur astronomy.  Dobson is the founder of the "sidewalk astronomy" movement -- that's when you set up your 'scope on an urban sidewalk and show the wonders of the universe (or at least the solar system) to passers-by.  We did this in London with Saturn.  (Some of the cynical Londoners couldn't believe it was real -- they thought I had a transparency in the scope tube.) Dobson developed a very simple and popular method of mounting telescope tubes -- the "Dobsonian" method.   

More on Dobson here: https://en.wikipedia.org/wiki/John_Dobson_(amateur_astronomer)

Below you can see a short update on Peter's homebrew airplane. 

Dust Storm on Mars

Damn.  Just as Mars gets close enough for me to see something with my 6 inch reflector telescope, a massive dust storm hits.  I was out there this morning at 0430 local.   Mars was bright and red in the southern sky, but when I got it in the telescope's field of view it was like looking at a red version of Venus -- just the disk, with no surface features visible.  The before-and-after pictures above (taken with far better equipment than mine) shows the extent to which the dust has obscured things on Mars. 

But Sky and Telescope reports that the Martian skies may soon be clearing.  Hooray!  

https://www.skyandtelescope.com/astronomy-news/observing-news/martian-dust-storm-2018/

On Field Day: The Marine Corps Antenna Manual

Don't let it be said that SolderSmoke made no contribution to Field Day!   Here is the USMC Antenna Manual.   Looks like there is lot of good info in there.   

https://www.marines.mil/Portals/59/Publications/MCRP%208-10B.11.pdf?ver=2017-03-15-092827-423

SolderSmoke #205 Solstice, Mars, Antennas, Displays, Phasing Fix, VFOs, Lexicon, MAILBAG

June 23, 2018

SolderSmoke Podcast #205 is available:  

http://soldersmoke.com/soldersmoke205.mp3

-- Summer solstice.  Mars Observations.  Graduations.  Internships.  Fathers Day.

-- Antenna Angst:  Pete's tribander and Bill's Moxon.  Insulation and resonance?

-- Pete's work on color displays. 

-- Bill goes back to fix up older projects:  

-- Fixing the Frankenstein Phasing RX.  Found an open choke!

-- Tightening up the HRO Dial. 

-- Achieving Juliano Criteria stability on a BITX20 VFO. 

-- Lexicon additions:  "Scratch Built"  "Hardrock Radio"  

https://english.stackexchange.com/questions/39551/where-does-the-saying-made-from-scratch-originate

-- PastaPete:  http://www.pastapete.com/

MAILBAG: 
Bob Crane W8SX Corrspondent at FDIM
Ralph AB1OP  Building LBS
Bruce KC1FSZ  Digital Pot
Jason W5IPA uBITX in Juliano Blue
Rogier KJ6ETL  ON THE AIR WITH A uBITX
Special thanks to Tim Walford for 25 years of Hot Iron.  

"Hot Iron" #100 -- Thanks Tim Walford!

Tim Walford, G3PCJ has put out issue #100 of Hot Iron, the Journal of the Constructors Club.  That my friends is a long time publishing a quarterly.  25 years!   And it is a wonderful publication, filled with ideas and inspiration.  

Tim tells us in #100 that he is passing the baton (the Hot Iron?) to Peter Thornton, G6NGR who will keep the iron hot from here on out.   Peter is looking for contributions for issue #101.  Please try to help him out.  

Thanks again to Tim.  Good luck with the farm and the house moves.  

Rockets and a Microcontroller -- Videos

https://bps.space/

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.