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[Articles Home]  [Add Article]  

10-Meter Dipole with 5 Db Gain

Dick Reid (KK4OBI) on April 16, 2014
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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’s de KK4OBI

 

Member Comments:
This article has expired. No more comments may be added.
 
sounds like Special Magic  
by KD0REQ on April 17, 2014 Mail this to a friend!
I'm thinking the cancellation of some radiation "over there" makes the radiation pattern "right at them" look like gain. without actually plotting the pattern with a field-strength meter, I'm skeptical.
 
RE: sounds like Special Magic  
by WB2WIK on April 17, 2014 Mail this to a friend!
[quote]The dipole is the basic building block of many antennas. A dipole does NOT have 2.2 dB gain over an isotropic radiator when the dipole is placed over earth. The dipole has about 8.5 dB gain over an isotropic radiator! Always remember this when you see antenna models over earth given in dBi. If the model over earth shows a "gain" of about 8.5 dBi, the model effectively has the same gain as a dipole.

Here is the pattern of a 145-foot high copper wire dipole over medium real earth on EZNEC:

dipole gain in dBidipole gain dBi





You can see the gain is 8.5 dBi, and it is just a simple dipole just over 1/2 wave high. Any antenna you model should always be compared to a standard like this!

The notion a dipole has around 2.15 dBi gain is only true for freespace.[/quote]

To see the NEC plots, they're from here: http://www.w8ji.com/antennas.htm

Anything less than ~8 dBi (bi-directional) for a dipole installed over earth is actually a bit disappointing.











 
RE: sounds like Special Magic  
by W4KVU on April 17, 2014 Mail this to a friend!
April 1st was a couple of weeks ago.....
 
RE: sounds like Special Magic  
by ZENKI on April 18, 2014 Mail this to a friend!
Stack 2 dipoles vertical and horizontal and you can have steerable/slew-able antenna array. You also get substantially more gain. I dont know any hams playing around with slewing curtain antennas yet.
 
RE: sounds like Special Magic  
by KK4OBI on April 18, 2014 Mail this to a friend!
I thought this might stimulate some interest.

After my initial dumb luck with an L-antenna came the question:
"What happens to a Vertical dipole when the lower arm is gradually bent upwards to an L and beyond".

An internet and antenna book search provided no details.

This brief article answers by modeling and by practical application.

Starting conditions: Vertical dipole at 28.4 MHz; #12 AWG; fed at mid-point 12 feet from ground; circular radiation pattern; gain <1 dBi; radiation efficiency 28%.

When bent, think of it as a quarter-wave monopole with one radial at various angles.

It can be configured at ~75 degrees for general purpose as a slightly directional quarter-wave vertical with mixed polarization; or at ~105 degrees as a bi-directional horizontal quarter-wave beam with 5 dBi forward/rear lobes and 5 dBi side/side attenuation. Efficiency 74%.

The next article deals with off-center feed of bent dipoles.
 
10-Meter Dipole with 5 Db Gain  
by KB4QAA on April 18, 2014 Mail this to a friend!
The author references his previous article posted on Jan 20th, 2014, which discusses OCF "L" with telescoping whips on 10m.

The author exemplifies 'random experimentation' by continuous changing various antenna characteristics, focusing on single measurement values at a given configuration and plucking explanations for any performance characteristic out of the air.

sigh.
 
10-Meter Dipole with 5 Db Gain  
by KB4QAA on April 18, 2014 Mail this to a friend!
KK4OBI:
You drag us across the countryside with all your modifications, assumptions and comments, leaving us breathless. It is impossible to intelligently address the article.

Bottom line: Choose your best design, state the parameters and performance claims!

Experimentation is always worthwhile, and even less than optimum antenna designs can teach us much. We need something more definite than a 'stream of conciousness' narration. 73, bill
 
10-Meter Dipole with 5 Db Gain  
by K8QV on April 18, 2014 Mail this to a friend!
This seems like how I set up the Buddipole in the field. It's quick and convenient, but that's about all. A horizontal dipole at a decent height will beat it every time. That's easy to do on 10 meters, but for 30 and 40 meters the Buddipole vertical with counterpoise is much simpler to use portable where you can't depend on tall enough dipole supports. If you can find one tall support, an end fed half wave works as well as anything. If you want gain over a dipole with a single wire, try a double extended zepp.

I'm no antenna expert, but I fail to see how what is essentially a 1/4 wave vertical with a single radial can outperform any normal dipole. Am I missing something?
 
10-Meter Dipole with 5 Db Gain  
by VE3XQQ on April 19, 2014 Mail this to a friend!
Interesting experiment, yet a half wave horizontal dipole over regular ground exibits 8Dbi.

De VE3XQQ, Frank
 
10-Meter Dipole with 5 Db Gain  
by W5GNB on April 19, 2014 Mail this to a friend!
The "Half-Wave Dipole" is used typically the standard of measurement and equates to a gain of Unity. If that dipole is disfigured in any way, it will loose efficiency thus reduce its "Gain" to something Less than Unity.

Also, if you do obtain a gain in some direction, there will Always be a LOSS of gain in other directions. You never get Something for Nothing.

If you are using something like Isotropic radiators for your gain reference, you can usually jiggle the numbers to say just about anything......

 
10-Meter Dipole with 5 Db Gain  
by K1DA on April 19, 2014 Mail this to a friend!
The term "gain" is misleading. An antenna is a PASSIVE device, when an antenna has a LOBE or "pattern" which is stronger in a particular direction and vetical angle than some other antenna, it is at the expense of a NULL in some other direction. That may be exactly what you want, but calling it "gain" brings to mind an amplifier, which it is not. Lets talk in terms of directivity or "front to side and front to back" instead.
BTW a lousy antenna which radiates only a small portion of what it is fed may still have some front to back or side difference but it sure ain't "GAIN". Witness the Beverage. There's no free lunch in the antenna business.
 
10-Meter Dipole with 5 Db Gain  
by JOHNZ on April 19, 2014 Mail this to a friend!
A student came to me a few years ago, excited over similar findings. Eventually, I convinced him to try a "hatted" vertical dipole for 10 meters. It is simple and cheap. Each end has a so called "capacity hat."

Required length of the spokes is dependent on the ratio of the main element diameter and the spoke diameter.

A true symmetrical hat assembly will give about the highest impedance for any type loading in conjunction with a fixed overall length.

Suggested good source of information is to find a local ham who has been licensed over 50 years. Guaranteed to get excited, when you mention this type antenna to him.
 
RE: 10-Meter Dipole with 5 Db Gain  
by W5HEH on April 22, 2014 Mail this to a friend!
Dick, Thank you for taking the time to share this, i am excited to try it . Forget about the critical /naysayers , they forgot what it means to go outside and experiment , i have not at 62 , i am having fun ,that is what this Hobby is all about - getting out and experimenting , congrats !
 
RE: 10-Meter Dipole with 5 Db Gain  
by KK4OBI on April 26, 2014 Mail this to a friend!
Avram,

See reply on your QSL.net email.

Dick
 
RE: 10-Meter Dipole with 5 Db Gain  
by K9MHZ on April 27, 2014 Mail this to a friend!
>>>>by K1DA on April 19, 2014 The term "gain" is misleading. An antenna is a PASSIVE device....but calling it "gain" brings to mind an amplifier, which it is not. Lets talk in terms of directivity or "front to side and front to back" instead.
BTW a lousy antenna which radiates only a small portion of what it is fed may still have some front to back or side difference but it sure ain't "GAIN". Witness the Beverage. There's no free lunch in the antenna business.<<<<


Well, that lobe WILL actually provide some extra microvolts to the front end of the receiving system, so in a sense using the word "gain" isn't so terrible. Yes, it does so at the expense of some other portion of its pattern, and absolutely there is no free lunch. I guess I'm definitely with your point whenever I go into an AES and see "Supergainer" written on the plastic pouch of some Diamond or Comet mobile antenna. Makes for a good chuckle about what sells.
 
RE: sounds like Special Magic  
by WR6J on May 1, 2014 Mail this to a friend!
I'm a bit confused. Did you model the horizontal dipole at 12' above the ground? If so it should have shown over 8dbi or another 3dbi higher than your L dipole.

Another way to look a this experiment is that you are starting with a horizontal dipole at 12' and showing that bending one arm down only loses you 3dbi.

Am I missing something?

73 from WR6J
Richard
 
RE: sounds like Special Magic  
by WR6J on May 1, 2014 Mail this to a friend!
I'm a bit confused. Did you model the horizontal dipole at 12' above the ground? If so it should have shown over 8dbi or another 3dbi higher than your L dipole.

Another way to look a this experiment is that you are starting with a horizontal dipole at 12' and showing that bending one arm down only loses you 3dbi.

Am I missing something?

Richard
 
10-Meter Dipole with 5 Db Gain  
by KF7VXA on May 23, 2014 Mail this to a friend!
I just went through the same attacks as you when I posted that the CCD antenna I just bought works better than the wire dipole I took down to replace it with.
I have yet to really study your post as well as it needs to be, but experience in the field with something counts for a lot.
Keep experimenting and have fun. If it works for you, it's your gain, the whiners loss.

73's John KF7VXA
 
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