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Antenna Gain

Robin Cross (W0FEN) on April 28, 2017
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Antenna Gain

First off, this article is misnamed. It should be called Antenna Directionality.

An antenna never has gain. An antenna seems to have gain because it has a form of directionalism that moves radiated power from where the designer didnít want it to where they did.

Many articles have been written about directionalizing HF antennas. When I decided to write this, I was not thinking of HF but VHF and UHF instead.

Many Amateurs install Omni-directional gain antennas at their QTH. This is wonderful IF the terrain is relatively level. I donít mean pancake flat. A few hills wonít hurt that much. If I lived in Denver and most of the repeaters I was interested in were on mountaintops then I should install a ľ wave ground plane. I will get into the mountaintops much better than a vertical gain antenna that has moved the signal down to 15 degrees above horizontal. In Kansas City, the terrain is quite variable. There are valleys that can be 30 or more meters below adjoining terrain. As a matter of practicality I have ľ wave antennas on both of our vehicles. This is so that the antennas donít hit the garage doors. We have a multitude of repeaters locally on every band from 6 M to 1.2 GHz. Here we donít have mountaintops. The best we can do are tall buildings [about 25 stories] or towers. The limit is about 160 M.

When installing a VHF antenna on a small ship. [not a luxury liner] A ľ wave ground plane will most likely work better than any omni-directional gain antenna. As the ship rocks with waves, the signal will still be in the main horizontal lobe of the antenna. Not many cars get to the angle that a ship can.

To visualize this, hold your hand out with the first two fingers in a V shape. Your fingers should be above and below horizontal. As you rotate your hand vertically, the limits of the main lobe of the antenna will move up and down. You signal will drop out of the repeater and then reappear. So sometimes more Ďgainí is not better.

As I said at the beginning, an antenna cannot have gain. To have gain it would need a source of power. Amplifiers have gain; antennas do not.

Robin Cross

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Antenna Gain  
by KJ4DGE on April 28, 2017 Mail this to a friend!
Thanks Robin,

Brought some ideas to mind as to experimental design actually.

RE: Antenna Gain  
by AA4PB on April 28, 2017 Mail this to a friend!
I understand your point, but it is common practice in engineering to compare antennas by describing their "gain" over a reference antenna in the primary direction. If an antenna has 3dBd gain, that indicates that in it's main lobe it's signal will be 3dB greater than a simple reference dipole. Of course the antenna obtains most of that "gain" by focusing the signal in a single direction, much like a reflector in a flashlight focuses the light all in one direction. The antenna can't create energy. Some "gain" can be obtained by reducing loss.

Gain figures give us a way to compare antennas and a fairly easy way to measure the difference. Granted, it's important to understand how that gain is obtained in order to select the best antenna for a particular application.
Antenna Gain  
by K0CBA on April 28, 2017 Mail this to a friend!
YIKES!! Someone who understands antennas.

Good write-up.
RE: Antenna Gain  
by W4XKE on April 28, 2017 Mail this to a friend!
Methinks you must have been in the Navy... Our old electronics instructor was a prior Navy radar technician and it always frosted him when people would say that an antenna has gain.

An antenna is passive and therefore it has no gain - only losses. Amplifiers have gain because the signal can be increased but an antenna is a passive device.

I suppose we can come up with all sorts of false concepts and debate on their validity - and what the word IS really means. :-)
Antenna Gain  
by WW8X on April 28, 2017 Mail this to a friend!
Kind of like: If you're standing beside a person using a firehose and then suddenly they turn the nozzle in your direction, the firehouse will appear to have plenty of gain. Even though itís the water system that's providing the power and the hose nozzle is merely directing it.
RE: Antenna Gain  
by AA4PB on April 28, 2017 Mail this to a friend!
Every engineering text that I've ever read says that antennas can have gain. You are defining gain to narrowly. Gain doesn't necessarily mean that the device makes a small signal larger (as in an amplifier). In the case of a passive antenna, gain is comparing the performance of an antenna against a designated reference antenna.

My Navy electronics instructor told us that studying about those new fangled transistors was a waste of time because they would never amount to anything useful. Boy was he wrong :-)
RE: Antenna Gain  
by W1PJE on April 28, 2017 Mail this to a friend!
A lot of the confusion here is POWER vs. POWER DENSITY.

When I teach undergraduates about antenna gain, I tell them that the gain refers to an increase in power DENSITY (Watts per m^2) in a given direction over a mythical isotropic antenna that sends the same power equally in all directions. (Examine your units, just like chemistry.)

No magic energy gain, because the same amount of Joules/second = Watts are put into the antenna terminals regardless of gain. But the power density of the E (or B) field delivered to a spot can be much higher depending on the antenna's gain.

Another way: if you imagine a sphere centered on your antenna, at a distance R away from the antenna, the power density provided by the antenna in the center of the beam is G * P / (4*pi*R**2). G = gain and has no units, P = power in Watts from the transmitter. For the denominator expression, Imagine the area covered by the inside of a sphere with radius R.
RE: Antenna Gain  
by K9MHZ on April 28, 2017 Mail this to a friend!
There you go, PJE....well put.

Nothing totally wrong with the term "gain", so long as the user knows there is no free lunch.
Antenna Gain  
by N6JSX on April 28, 2017 Mail this to a friend!
OMG, his second paragraph undid any good intent he may have. Then a 1/4 wave at sea is better than a 1/2 wave,i.e. J antenna on VHF, as bouncing in the waves evens everything out?!@#$%^&*.... Does he know anything about 'angle of radiation or real measured radiation patterns'? He needs to check the Marine band antennas and get surprised....

Yup, per him, a directional-omni will get you that gain and ERP you're seeking.... Wonder if he can give you a beam-bearing using that omni for max ERP....

This is a good April 1st article. The worst of it is now that this is published he now an authority --- the ignorant will believe this tripe. Only one credit point I'll give him at least he didn't try to sell that a 1:1 VSWR will improve the actual antenna gain.
RE: Antenna Gain  
by KC7MF on April 30, 2017 Mail this to a friend!
Gain is a function of the amount of money someone has divided by the nastiness of the HOA.

For example. If "Joe" has a million dollars for an antenna but the HOA is a million times nastier than Joe is then Joe gets a hidden dipole which equals no gain.

On the other hand if Bill has $20,000 dollars for a tower and antenna and the HOA is run by preppers then Bill gets as much as 7 DB gain; or even more if Bill reads the claims on the antenna advertising gain. He also gets an offer by the preppers to enclose his house in a Farady cage but then I digress.

There is another factor, rarely discussed, called WPF. This stands for "Wife Permissiveness Factor". This can act as a multiplier when discussion the station's antenna budget. It can also lead to the least efficent antenna known to man called the "screwdriver" antenna. Its principle cause is the inability of the ham(especially no-code extras)to explain to the XYL why she can't touch the antenna but a bird can.

There is a similar but rare limiting factor mostly applying to ground mounted verticals. Most think that radials are the big thing but they are not. The big thing limiting ground mounted verticals is the LDWPOTAWT conundrum. This has really limited the effectiveness of ground mounted verticals for some hams. It stands for Likelihood Dog Will Pee on the Antenna While Transmitting conundrum. I am sure there is an AARP paper about the maximum safe RF entering dog naughty-bits but I can't figure out how to phrase the search term without being kicked out of AARP.

I may write an article about these things some day. There are many more factors that the OP seems to have left out.
RE: Antenna Gain  
by K9MHZ on May 1, 2017 Mail this to a friend!
"Gain is a function of the amount of money someone has divided by the nastiness of the HOA."

Ha, that's not bad!
Antenna Gain  
by KC4ZGP on May 1, 2017 Mail this to a friend!

Your data is non-errored.

Antenna gain is as correct to say as it is correct to say a transmitter's impedance is 50 ohms.

73 and wear that seat belt.


Antenna Gain  
by KE4ZHN on May 1, 2017 Mail this to a friend!
An antenna has no gain. It can focus the radiation pattern to favor a direction, making it appear to have gain, but it has no way of increasing the RF power fed to it. It does in fact lose some RF energy due to feed line and conductor losses in the antenna system.
RE: Antenna Gain  
by K6AER on May 1, 2017 Mail this to a friend!
All antennas have +/- gain when referenced to some other radiator.

Isotropic source can have gain over a dummy load.

And yes, I have worked stations on a dummy load.
RE: Antenna Gain  
by AA4PB on May 1, 2017 Mail this to a friend!
ZHN: You are defining "gain" to narrowly. Take a look at:
RE: Antenna Gain  
by K9MHZ on May 2, 2017 Mail this to a friend!
"Antenna gain is as correct to say as it is correct to say a transmitter's impedance is 50 ohms."

Yeah, but.... (always a big butt)

I think you guys are getting wrapped around the axle with the word "gain" as it applies to antennas. Maybe back in the day, different word(s) choices would have been better, describing the benefits of increased power densities in directions/planes with different antenna designs and configurations.

Can we get past these posts trying to make people think we're so smart because we have problem with the word "gain" as it relates to antennas?

Point made, guys. The horse is dead and the fat lady has sung.
RE: Antenna Gain  
by K9MHZ on May 3, 2017 Mail this to a friend!
Excellent reading. Check out page 40.....
Antenna Gain  
by N8EKT on May 10, 2017 Mail this to a friend!

I found out decades ago that gain becomes your enemy in hilly terrain

While most ham and commercial repeaters were using massive gain antennas, I went with lower gain and had better coverage with half the power

To this day I still see Motorola engineered repeater systems that cover 40 miles away better than they do in the area that they are LICENCED to serve

Antenna Gain  
by AE9C on May 30, 2017 Mail this to a friend!
Robin,,Your spot on! I agree>>...
Antenna Gain  
by 3U419HF on June 8, 2017 Mail this to a friend!
I'm sorry, but you are talking a lot of clap trap.

You are trying (unsuccessfully) to redefine antenna terms, that are used both by amateurs and professionals. I'm NOT an American, but the terms accepted by most antenna professionals are from the American Institute of Electrical and Electronic Engineers (IEEE). The IEEE Std 145-1993 "IEEE Standard for Definitions of Terms for Antennas" defines antenna terms, and defines gain. It also defined "directivity" - not the "Antenna Directionality." term you seem to have invented.

Of course a passive antenna does not have power gain - although active antennas do.

I question why you feel the need to try to redefine terms which are well known by hams, and professionals. Nobody in their right mind would suggest a passive antenna has power gain, but it does have "gain", relative to that of an isotropic radiator.

I would suggest that if anyone wants to learn about antenna terms, they consult the IEEE standard "IEEE Standard for Definitions of Terms for Antennas" and not yourself, QST or any other dubious source. Books by Balanis, Krauss (SK), etc all define antenna gain.

RE: Antenna Gain  
by K9MHZ on June 8, 2017 Mail this to a friend!

Not sure where the "antennas have no gain" thinking comes from. Pretty boilerplate concepts in radio. Years ago, we were to never fly over the Goldstone high gain dish east of Edwards. If people have a problem with that word as applied to antennas, they'd better run it by NASA among others, since obviously those organizations are misinformed. <eye roll>
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