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Saturday, July 14, 2018

Homebrew Tuner for Doublet Antenna

For now, I've put the Moxon project on the back burner.  I will take it up again once Old Sol starts showing some spots.  In its place a 135 foot doublet is going up.  I got at a hamfest a while back.  (It is the only HF antenna that I ever bought!) It is the SPI-RO Manufacturing Company's Model A-10.  It came with 100 feet of 450 ohm window line.   It will be up on the roof soon.  

Today I put the tuner on the wall in the car port right outside the shack. I even built a little shelf for the SWR meter (used one of those Whole Food grilling planks!).  I put a 25 ohm resistor where the feed line will connect.  I was able to tune it up on the two bands I tried: 40 and 17.  

There is a smaller coil inside the big one -- the smaller coil resonates with the lower variable cap. 

You can see all the homebrew rigs in the background -- waiting patiently for the antenna.  

I actually built the tuner back in 2012, but never used it.  Description here: 

I will try to provide a schematic and more details soon. 

Tuesday, July 3, 2018

The Moxon Files from L.B. Cebik W4RNL

I had thought that the Cebik files were lost to us in some sort of legal copyright struggle.  But in my effort to better understand the Moxon antenna, I found a real treasure trove of Cebik's writing.  These should all be saved somewhere safe. 

I especially liked his description of the evolution of the Moxon antenna.  Les Moxon was apparently very unAmerican in his emphasis on reception (not transmit gain)  as the main benefit of the beam antenna.  He also sought to avoid superfluous luxuries like rotators, but Cebik hints that rotators have become an important part of our American way of life.   Indeed.   
Before I found these files I had been on the verge of giving up on efforts to replace my storm-damaged Moxon.  After all, solar minimum is still ahead of us.   But after reading OM Cebik's articles I have decided to build a 20 meter version and place it above the center point of a 130 foot doublet.  I will have the best of both worlds.

L. A. Moxon, in his HF Antennas for All Locations, provides the essential clue: "the main benefit [of a beam] accrues from the reduction of interference during reception, though the 4 to 6 dB gain provided by typical amateur beams is an important bonus and probably the reason which carries the most weight with the majority of amateurs."(2)Here is a theory of beam operation quite unAmerican is style: instead of gain, Moxon strives for front-to-back ratio as the most crucial aid to ham operation. His statement is an affirmation of the "good ears" theory of operation. Even more, it forms the basis for his rectangular improvement upon the VK2ABQ square.
 Moxon prefers matched elements, tuning each of them to optimum performance remotely. That way, he can reverse the beam and do away with expensive and maintenance-intensive rotators. However, rotators are a way of life in the U.S. (a TV rotator will likely handle a 3-band Moxon beam), and there are many uses for portable beams that are hand-rotated or fixed in the field. Thus, I decided to continue the exercise in unequal element lengths.

Finally, a treasure trove of Cebik's writing:

Sunday, July 1, 2018

VU3XVR's Assembly Language 1K AtTiny-Si5351 VFO

Although Ram VU3XVR's project is in the digital realm, his barebones approach to the bits and bytes is, for me, very appealing. He takes a Si5351 and runs it with ATtiny13 with only 1k of space.  He makes intelligent use of every bit of that space.  He reveals his overall approach to rigs when he states in the video that his VFO will NOT have the traditional glowing numeral frequency readout because those bright lights can be so annoying and distracting.  I'm with your Ram!  Well done OM. Simplicity is a virtue. No more trouble with the Arduino and its fickle IDE.  No more agonizing visits to the Si5351 library.   

I see lots of applications for this little circuit.   Ram mentions beacon transmitters.  

He provides details here:   

Saturday, June 30, 2018

Tom Swift had The Knack

Thanks to Richard for alerting us this important piece of Knack history.  Not bad for 1910.  You can see Tom's shack and antenna in the cover image (above).  I don't think he was going for a fan dipole.  He built the kind of multi-wire antenna that was in fashion in the early days of radio. 

The full text of the book is avaialble free on-line.  The radio fun begins in  Chapter 20: 

Bless my door knob, this was a lot of fun! 


I am certain I missed the origin of “the knack” as used on your blog. I, wonder, however, if in your youth you read Tom Swift novels? Although now they seem somewhat politically incorrect, I feel that the word may have, for our purposes, evolved there.

In the first novel, “Tom Swift and His Motor-Cycle” (sic) Tom repairs a butter churn’s “system of  cogs and handles.” When praised for his abilities he declares, “It’s just a knack.” Stick with me.

In a later novel, written around 1910, “Tom Swift and His Wireless Message” Tom is shipwrecked on an ebbing volcanic island. He saves the day by constructing a transmitter and receiver from the wreckage of his plane,  even though he “did not have the magnets, carbons, coherers and needles” needed. He strings “ wires from the top of the dead treed, to a smaller one, some distance away, using five wires, set parallel, and attached to a wooden spreader, or stay. (Fan dipole?) The wires were then run to the dynamo, and the receiving coil, and the necessary ground wires were installed.” Then,”once the impulses, or electric currents, are sent out into space, all that is necessary to do is to break, or interrupt them at certain intervals to make dots, dated and spaces.” He sent “C.Q.D. (come quick—danger) even though a “new code has been instituted for them, but I am going to rely on the old one, as, in this part of the world, the new one may not be so well understood.” Needless to say, a ship hears, responds and rescues the crew.

That”s “the knack", alright!

Never give up, and 73.
Richard, KD0NPM

Friday, June 29, 2018

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:

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

Monday, June 25, 2018

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!  

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