Lobes, Nulls, and "Gain Dipoles" -- Testing the Theory with WSPR

In the last podcast Pete and I were discussing dipole antennas.  We mentioned dipoles that were multiples of 1/2 wavelength and said the result could be a "gain dipole."  This provoked some head scratching.  Listener Riley asked for more info. See the comments section under this post: http://soldersmoke.blogspot.com/2020/05/soldersmoke-podcast-222-antennas.html. 

A short time later Pete was corresponding with Brad WA8WDQ who had questions about his antenna pattern.  Pete recommended using WSPR to test his antenna's effectiveness. 

These two exchanges got me thinking about the radiation pattern of my 135 foot doublet antenna, especially on 20 meters.  Where are my lobes, where are my nulls?   Following Pete' advice I turned to WSPR.   But first, a quick look at the PREDICTED patterns.

ON5AU has on his site a great article by antenna guru L.B. Cebik  W4RNL with exactly the info I needed.  Above is W4RNL's chart of predicted radiation pattern for 20 meters on a 135 foot doublet.  Note the orientation of the wire.

My antenna is oriented almost exactly north-south (broadsides to the east and west).  So with a standard north at top map, my pattern on 20 should look like that of W4RNL's chart.  What did I get from WSPR?   Here is the pattern for an hour or so of 250 milliwatt transmissions from my station using the 135 foot doublet on 20 meters (using homebrew balanced tuner): 

You can clearly see at least three of the four predicted lobes (NE, NW, SW). 

Now, part of this WSPR pattern could, I suppose, be the result of the geographic distribution of WSPR stations.  If there are just more of them in the areas where I am seeing lobes, the pattern could just be the result of geographic distribution.   I don't think that is the case, but to test this idea (a bit) I decided to look at the 40 meter pattern.  

Here is what W4RNL predicted (same north-south antenna orientation): 

And here is the WSPR map that I got, again using about 250 milliwatts for about an hour): 

I think this pattern matches nicely with the prediction.  You don't see the nulls that you see in the 20 meter pattern.  You do see some stations directly north of me (as predicted).  There does not seem to be a big disparity in the geographic distribution of WSPR stations.

One note on the use of WSPR:  I started out using WSPR in receive mode, thinking that the pattern I'd see would be similar on receive or transmit  due to the antenna reciprocity principle.  But I worried that the results could be easily skewed by higher power WSPR stations.  So I shifted to the transmit mode and limited my output to 250 milliwatts. 

Here is the W4RNL chart showing the patterns for all the bands: 

http://on5au.be/content/a10/wire/abd.html

Here is the azimuth chart for my location: 

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

LB Cebik, WN4RNL, and the "Ham Spirit"

As all of you probably know, LB Cebik, esteemed antenna expert and mentor, recently passed away. This morning I happened to find his entry on the wonderful "Novice History" web site:
http://www.novice.bappy.com/index.html

Note what LB says about "the ham spirit."

L.B. Cebik, W4RNL (WN4RNL, 1954)
I was licensed in 1954 as both a Novice and a Tech, since
then you could take both exams in one session and
privileges were separate. (W1APS/WN1APS)I got on
the air for the first time with a ham a couple of blocks away,
an fine old timer.

However, I got key fright half way through. My dad,
James S. (Jim) Cebik, came to my rescue and finished
the contact, although he had not touched a key in
over 20 years.

Jim Cebik had been 1ATG and later W1BUK in the late
1920s and early 1930s (and wrote a few articles on
his experiments). He gave up amateur radio
when he married in the depression years. Relative
parts costs were high, and family came first. In fact,
he rarely mentioned amateur radio, and my
entry was independent via some high school
comrads and a cousin. But he had not forgotten
his CW or key skills and saved me from
embarrassment on that first day. I returned the favor
by renewing his interest in amateur radio
and about 1964, he was relicensed and obtained
his old W1BUK call, which he used for very many
years. He died in 2002 in his high 90s.

So my Dad was a part of my Novice beginning
in amateur radio, and I strove to send CW with
a straight key so that one could not tell it from
a keyer.

He remains a strong part of my effort. He noted
that the ham spirit is to give, if needed, the shirt
off one's back to a fellow ham and to expect--not
its return--but rather that it be passed on to the
next ham who needs it.
That is the spirit of my web site.

My Novice days were a joy, and I have been
pleased to carry my father's amateur radio days
into everything that I do.

Hope this is useful.
-73-
LB, W4RNL