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10-Meter Dipole with 5 Db Gain

Created by Dick Reid, KK4OBI on 2021-08-20

"Editor's Note: Due to the popularity of some of eHam's older articles, many of which you may not have read, the eHam.net team has decided to rerun some of the best articles that we have received since eHam's inception. These articles will be reprinted to add to the quality of eHam's content and in a show of appreciation to the authors of these articles." This article was originally published on: 04/16/2014



10-Meter Dipole With 5 dBi Gain

No reflector. No director. No radials. Less than a quarter-wave turning radius. Close to the 6dBi of a Moxon plus bi-directional! How can this be? I too was surprised when I stumbled onto it. Let me tell you how.

Recently I have been using and optimizing a variant of the off-center-fed (OCF) L-dipole initially described in e-Ham article #31424. To compare performance to my conventional 10M dipole I bought an antenna switch at the recent Hamcation Orlando. Now when transmitting, this allows me to rapidly switch antennas so that other hams could tell me which antenna is stronger. Also by switching when listening, I sorted out the L-dipole directional characteristics and curiously, noted polarization meandering on multi-skip/path signals. Overall the results were quite satisfying but raised the question: What are the effects of changing the angle of the lower arm of a bent vertical dipole?

To find out the effects, I turned to wire antenna simulation by using the modeling program 4NEC2. This allowed the setting of dipole height over ground, length of dipoles and bend angle of the lower dipole arm. Here are the results graphically.

Bent Vertical Dipole

 

Effects of changing the angle of the lower arm of a vertical dipole

Following is a verbal summary of the associated 4NEC2 polar plots and color 3-D images.

Basic Vertical dipole. 10 meters, 12 feet high, #12 AWG wire

  • Omni-directional pattern. Vertical polarization. 1.03 dBi at 10 degree angle from ground
  • Secondary lobe at 40 to 50 degrees up from ground
  • No skyward radiation
  • Z=70 ohms, SWR=1.4

Lower arm raised 30 Degrees away from vertical

  • Circular pattern skews outward toward the direction of arm (3 o'clock direction looking down)
  • Gain increases to 1.7 dBi at 40 to 50 degrees. Lobe extends from 2 to 4 o'clock.
  • The 10-degree lower lobe also extends 2 to 4 o'clock
  • Vertical radiation polarization. No skyward radiation
  • Match improves: Z=67 ohms, SWR=1.35

Lower arm raised 60 Degrees

  • Stronger directional pattern broadly pointing from arm.
  • Gain increases to 2.76 dBi at 40 degrees. Lobe extends from 12 to 6 o'clock
  • The 10-degree radiation lobe extends also from 12 to 6 o'clock
  • Mostly vertical polarization. A little skyward radiation
  • Frequency rises slightly. Match improves: Z=57 ohms, SWR=1.15

(Note: 50 ohm impedance and balance between vertical and horizontal polarization occurs with lower arm at 75 degrees).

Lower arm at 90 Degrees

  • Horizontal pattern develops broadside to the arm.
  • Gain focuses to 4.12 dBi at 20 to 30 degrees pointing to 12 and 6 o'clock
  • The 10 degree radiation unchanged from 12 and 6 o'clock
  • Pronounced upward radiation
  • Frequency rises. Match drifts downward: Z=41 ohms, SWR=1.22

Lower arm at 120 Degrees up from vertical

  • Strong, low angle horizontal pattern entirely broadside to arm
  • Gain focuses to 5.37 dBi and sharpens down to 20 degree lobes pointing tightly at 12 and 6 o'clock
  • Side rejection is 5.3 dbi between 9 to 3 o'clock
  • Skyward radiation makes pattern look like a flying saucer
  • Frequency jumps. Match needs tuner: Z=23 ohms, SWR=2.18

Generally,

  • For angles 90 degrees up, aim horizontally from side of arm for high gain DX
  • For angles around 60 degrees, the arm points to wide coverage area with some gain
  • Angles between 60 and 90 degrees, mixed vertical and horizontal polarization for general purpose
  • Frequency increases by the antenna becoming shorter and electrically wider. Past 90 degrees inter-arm capacitance dominates. Retuning for resonance at extreme angles produces no noticeable effect on SWR.

 

Currently I use the L-Dipole set to about 100 degrees for DX East to West. My horizontal half-wave dipole is for North to South. If I get excited about getting into a pile-up, I will go out and aim the L-Dipole. And yes, I have thoughts about a rotator and remote angle adjustment as well as having dabbled with vertical tilt to aim the angle of radiation lower.

73 de KK4OBI

 

WB4DX2022-04-13
Re: 10-Meter Dipole with 5 Db Gain
Good one!
Reply to a comment by : ZL1RD on 2021-09-03

Another "expert" that has no idea what an antenna is or how it works. Dipoles do not have 5db gain... period.
ZL1RD2021-09-03
10-Meter Dipole with 5 Db Gain
Another "expert" that has no idea what an antenna is or how it works. Dipoles do not have 5db gain... period.
KT4WO2021-08-21
Re: 10-Meter Dipole with 5 Db Gain
I want one of those 6dbi Moxons!!! lol
Reply to a comment by : W4OP on 2021-08-21

Wait a minute. You are comparing your antenna above real ground with a Moxon in free space.Did you model a Moxon above real ground at the same height as your L? I think you will be very surpised that the gain you ascribe to the Moxon is about 6dB below a Moxon above real ground. Dale W4OP
W4OP2021-08-21
10-Meter Dipole with 5 Db Gain
Wait a minute. You are comparing your antenna above real ground with a Moxon in free space.Did you model a Moxon above real ground at the same height as your L? I think you will be very surpised that the gain you ascribe to the Moxon is about 6dB below a Moxon above real ground.

Dale W4OP