[TenTec] limited to one antenna

[TTMaven]

On 5/23/2014 8:23 PM, Paul DeWitte wrote:

> As far as an 80m dipole being directional on the upper bands, if you
> have your resonant 10,15,20m dipole up high it will also be directional
> broadside. So what is the difference? Maybe just not the direction you
> want.
>
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I take your question to be:  what is the difference between a big dipole 
that can work the upper bands, and a smaller "resonant" dipole that is 
cut for one or more upper bands, respectively.   (By "resonant"  I 
presume you mean a half-wave dipole.)

Rick taught me an important lesson about long dipoles vs short dipoles. 
  Joel Hallas teaches the same lesson about big vertical antennas in his 
series of articles on vertical monopoles which appeared in a couple 
issues of the 2013 QST magazine.

	The longer the element is relative to the
	frequency, the more lobes it tends to have,
	and the radiation pattern varies, as well.

Joel Halls refers to this when he discusses the 43 foot vertical 
antennas in QST magazine last year.  At 80, 40, 20, and maybe 17 meters, 
it tends to have lower take off angles and fewer lobes.  But, as you use 
it on 12, 10, and maybe 60 meters, the take off angle rises, and you 
tend to get more lobes.   In comparison, a shorter ground plane for 
those upper bands will have fewer lobes and lower angles.

The long dipoles exhibit a similar phenomenon.  As you use a very long 
dipole on the upper bands, you tend to get more lobes and a different 
radiation pattern.  In contrast, a shorter dipole, cut for each band, 
respectively, will tend to have fewer lobes and a more rounded, better 
radiation pattern.

I believe the charts in Section 2.1.4  Effect of Frequency on Radiation 
Pattern (page 2-9 of the ARRL Antenna Book (22d Ed) show various 
radiation patterns for various frequencies of a fixed length dipole.  As 
you get more lobes, you lower peak gain and end up with nulls that may 
mean you don't hear the DX as well in certain directions.  Of course, 
some patterns may help matters, others will not.

In Chapter 10, on page 10-20, it says about 43 foot vertical multiband 
antennas:

	In recent years, the 43-foot ground-mounted vertical
	antenna with an automatic antenna tuner at the base
	of the antenna has become very popular as an all-
	band HF vertical...  while the elevation angle of
	maximum radiation begins to increase significantly
	above the 20 meter band, the combination of
	simplicity and clean appearance make up for the
	compromise.  ...

Joel Halls told us in his QST series of articles, that as you use those 
antennas on the upper bands - i.e. 17 meters and higher - you also get 
multiple lobes in addition to how the elevation angle rises, so you may 
be better off with a smaller, dedicated, tuned and "resonant" ground 
plane cut for the upper bands, than to try to use the big stick on the 
upper bands.  Rick has reinforced these observations for me on several 
occasions.

Thus, while matching the antenna to the transmission line and rig is one 
important consideration, the radiation pattern is another.

I think is explains the difference in the two types of antenna.  Of 
course, if you only have room for one antenna, then the long, multi band 
all-in-wonder is what you use!

Happy trails.
--------------------- JR  -----------------------