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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.  






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.  

http://www.antentop.org/w4rnl.001/mu0.html

http://www.antentop.org/w4rnl.001/mu2a.html

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.

http://www.antentop.org/w4rnl.001/mox20.html

Finally, a treasure trove of Cebik's writing: 

http://www.antentop.org/w4rnl.001/radio.html


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: 

https://vu3xvr.blogspot.com/2018/07/si5351-dds-clock-generator-using.html   
Designer: Douglas Bowman | Dimodifikasi oleh Abdul Munir Original Posting Rounders 3 Column