HOW DOES A DIPOLE HAVE GAIN OVER A DIPOLE ?

 As you may have noticed I am fascinated with wire and vertical antennas . I think I have built them all. EDZ,Half squares , OCFs -- you name it.  But I completely over looked the dipole because I thought thought  is was a base line antenna. I want to dispel you of that notion. To understand my point you must understand the confusing antenna gain game known as " DBI and DBD ".  To understand that I was educated by this simple explanation. DBI is gain over isotropic. "Isotropic" radiates is all direction like the Sun. a vertical is a half sphere isotropic ( "Radiating poorly in all directions) . If you see 7.5 DBI it means that the beamed power in some  direction is that many DB above isotropic , DBD is gain over dipole but watch this. DBD is uniformly considered 2.15 DB above DBI. Do if you have 7.5 DBI that antenna is 5.35 DB gain over a dipole. Theoretically , 3 db over Isotropic DOUBLES your power in that direction. That direction is mitigated by angle of radiation but in the maximum angle of radiation  this is the accepted gain in POWER. So if you see a 7.5 dbi -- we see  a reative power gain ( against isotropic) of   what?  Well at 3 db it makes that  2 times the powerer but what about 6 dbi?? It doubles the " 2" to 4 times  that. When you get 7.5 dbi you extrapolate to 5.5 times your power isotropic.

Now remember if you see DBD -- it is 2.15 db LOWER that DBI.

I want to pass along the fascinating graph from this work on this website  https://www.qsl.net/aa3rl/ant2.html By Mike Banz ,AA3RL. and particularly this chart. Look closely !
The table below tabulates the results. In the first two columns, the antenna's height above ground is given in wavelengths and in feet. The next two columns show the maximum gain in the favored direction (i.e. broadside to the wire), followed by the launch angle and the -3 dB vertical beam width. The next two columns once again present the gain and launch angle / beam width, but for the axial direction (off the ends of the wire). Finally, the last 2 columns list the complex impedance at the feed point, and the actual resonance frequency at that specific height.

Height	Height		Fav Dir	Fav Dir		End Dir	End Dir
				Launch			Launch
Wave			Gain	Angle/		Gain	Angle/		Feedpt	Res.
Lengths	Feet		(dbi)	Bmwidth		(dbi)	Bmwidth		Z	Freq
4.0*	560		7.75	4 / 4		5.57	72 / 13			6.93
3.0	420		7.83	5 / 5		5.25	68 / 14		77+ j11	6.94
2.0*	280		7.80	7 / 7		0	39 /		75 + j12	6.95
1.5	210		7.72	9 / 10		-2.50	33 /		75 + j11	6.96
1.0*	140		7.64	14 / 15		-11.00	20 /		74 + j08	6.96
.9	126		7.03	16 / 17		-8.30	22 /		85 + j13	6.94
.8	112		7.16	18 / 19		-6.40	25 /		84 + j26	6.88
.7*	98		7.95	20 / 22		-4.50	30 /		70 + j30	6.88
.6	84		8.35	23 / 26		-1.95	40 /		60 + j16	6.94
.5*	70		7.45	28 / 33		-0.51	43 / 33		71 - j00	7.00
.4	56		6.06	35 / 47		1.30	59 / 102		93 + j04	6.98
.3*	42		5.59	50 / 137		4.71	90 / 80		100 + j32	6.86
.2	28		6.70	90 / 118		6.70	90 / 67		71 + j56	6.77
.1*	14		8.21	90 / 103		8.21	90 / 66		23 + j39	6.84
.05	7		9.61	90 / 99		9.60	90 / 72		7 + j12	6.95

 I applied this to my test 18.1 mhz Dipole. Note that by proper elevation just above 1/2 wavelength you actually have a dipole at that height with 8.35 dbi!!  in the direction of directive which is broad side. Now notice even at quarter wave height you have 6.06.  So a 40 meter dipole  at 33 feet is showing gain. In fact , as noted above, if DBD is 2.15 d of DBI We are showing a Dipole with gain over a dipole of 3.91 db or a doubling of power, But you can see what you can do on 20 meters  at 33 feet!! 7,45 and if you can get it at 40 feet -- 8.35 DBI!!  That is why I dis my 17 meter at 37 feet and it is simply outstanding.  Dont over look the dipole!! So easy-- no balun . Just fly the damned thing and trim it to resonance. 

Mike W5ZO.