RadioBanter - Yagi efficiency

RadioBanter (https://www.radiobanter.com/)

- Antenna (https://www.radiobanter.com/antenna/)

- - Yagi efficiency (https://www.radiobanter.com/antenna/105045-yagi-efficiency.html)

On 24 Sep 2006 13:41:43 -0700, "art" wrote:

you know quite well what the post that started this thread asked for.

Yes, it is quite clearly offered in the Subject line, isn't it?

People are quibling over the word "efficiency" which I find rather
wierd
And that is the second word of only two words in the Subject line,
isn't it?

when we talk of efficiency one must multiply the ratio by 100
Are we to expect 96 more duplications of your post?

73's
Richard Clark, KB7QHC

Bill,
None of that is really a problem to me.I have multi points to which I
can feed for different patterns depending on the time of the day as
well as option of tilting the array. If I don't get my elmer I will
assume he is not on the air and yes it is twenty meters and I am
located in the couintryside that I understand is the highest between
Chicago and New Orleans and since this is the bread basket of the U.S
the ground loam is excellent. I use 7/8 andrews plus a long length
underground and the tower is hinged in two places
as well as another one for array tilting. I have power gain over a yagi
but I was just curious as to how much more radiation energy was
available to ensnare which Is why I referred to array volume since gain
is really dependant on half power beam width required or one can live
with I once had a 80 foot yagi and with the looseness in my prop pitch
rotor combined with the narrow beam one was never sure if one was
really taking advantage oif gain available. Pretty simple question for
those who know the answer after all you start off with 3 db gain in two
different directions thereffore it would seem to me that a yagi was
only 50% efficient but people are quarrelling about every thing except
the posed question to excuse them selves from real thought. Reg would
have come up with the solution after a bottle of wine after noticing
the english provided by the cue
Regards
Art

wrote:
art KB9MZ wrote:

Thus my major lobe needs to be robust between about 10 degtrees and 4
degrees to ensnare most of the communication.

I don't recall you stated which band but I'll assume 20 meters.
Assuming flat terrain (for your Indiana QTH), a single Yagi at 120'
(your maximum possible) would cover these angles best. 140' (or 2
wavelengths high if it is not 20m) would be the optimum heightl to
center your main lobe at 7 degrees.

Two stacked Yagis at 60' and 120' would be better than a single one at
120' or 140' for 4-10 degrees, but obviously this means more work and
expense.

If your terrain is not relatively flat, and if you are lucky to be on a
hill with a gentle slope in the direction of England, the optimum
height will be much less. However you would need to model this using
HFTA in the most recent Antenna Handbook or YT in older editions.

73, Bill W4ZV

art wrote:

The subject was antenna radiation patterns and ascertaining the
relative volume of the main lobe which is the reason for an antenna and
comparing it to the total volume of the array which one accepts to
obtain the desirable primary lobe.

Take the integral of the gain of the antenna over the angles in azimuth
and elevation that you consider to define the boundaries of the main
lobe and divide that by the integral of the gain of the antenna over
all angles . You'll need your gain as a function of the angles.

That's the number you're looking for, I suppose. I guess it's a decent
measure of sidelobe suppression... but so is the ratio of the gain of
the main lobe to the gain of the biggest sidelobe.

73,
Dan

Dan wrote:
"---of course at that point you could just run open wire line to any
distant receiver."

Yes, if it isn`t too distant.

If the 1000-mile open wire line lost 0.1 dB per 100 feet, loss would be
52.8 dB per mile or about 53 thousand db in its entire length, hardly a
useable transmission line.

On the other hand, suppose the wavelength were 160 meters. In the first
wavelength of a radio signal radiated in free space, you would lose 22
dB. In the second, you would lose an additional 6 dB. Doubling the
distance again to a total of 7 wavelengths, or 1120 meters, total space
loss would be 34 dB.

At a distance of 2240 meters from the transmitter, the loss is 40 dB
which is less that our open wire line would lose in its 1st mile, a
shorter distance.

Every mile of wire line extracts the same loss. Very long wire lines
become useless without repeaters to boost signal above the noise level.
Doubling line-of-sight radio path distance only increases path loss 6dB,
no matter how long the path is.

As for efficiency, J.D. Kraus says:
"The efficiency of an antenna is defined as the ratio between the power
radiated by it and the power delivered into the antenna." (page 866 of
3rd ed. of "Antennas".

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Dan wrote:
"---of course at that point you could just run open wire line to any
snip.

As for efficiency, J.D. Kraus says:
"The efficiency of an antenna is defined as the ratio between the power
radiated by it and the power delivered into the antenna." (page 866 of
3rd ed. of "Antennas".

I would think that the definition quoted was more applicable for a
radiator
than a antenna since the latter consists of addative and so called
destructive radiation. If an antennas radiative field was totally
destructive
the definition stated would include that as an efficient antenna !
Art

Best regards, Richard Harrison, KB5WZI

Hi Art,

A few points below, but first just remember that the TOA of any
horizontally polarized antenna is primarily a function of ground
reflections which vary according to height above ground. Previously
you mentioned that your antenna was designed for a TOA of 10 degrees.
That cannot be true except for a specific height above ground. Whether
Yagi, Quad, Log, Rhombic or any non-vertically stacked antenna.
Something like a Sterba curtain is different because it has multiple
elements stacked vertically which CAN be steered by phasing.

art wrote:

yes it is twenty meters and I am
located in the couintryside that I understand is the highest between
Chicago and New Orleans and since this is the bread basket of the U.S
the ground loam is excellent.

1. Absolute height above sea level means nothing. What is important
to TOA is your relative height above the terrain within a mile or two
of your tower. I operated from Colorado for ~30 years and always got a
chuckle from the guys who said, "My antenna is over 1 mile high". In
fact what is important for determining TOA is not height above sea
level but height above surrounding terrain.

2. Ground conductivity has minimal effect on horizontally polarized
ground reflections. You may be thinking of vertically polarized
antennas like verticals where it has a huge effect. HFTA does have
conductivity as an input parameter but it has minimal effect, at least
in my case (average ground versus salt water).

I use 7/8 andrews plus a long length
underground and the tower is hinged in two places
as well as another one for array tilting.

Phsical tilting has minimal effect on the ground reflections for the
angles of interest (4-10 degrees) because the vertical lobe is not very
narrow (typically a Yagi has ~50 degree 3 dB vertical beamwidth). In
other words tilting has a far secondary effect on TOA versus changing
the antenna height. You can prove this to yourself by modeling with a
program like EZNEC (HFTA does not allow tilting because it is
physically impractical and has little effect).

Pretty simple question for
those who know the answer after all you start off with 3 db gain in two
different directions thereffore it would seem to me that a yagi was
only 50% efficient

I believe you're referring to a dipole which has 2+ dB gain over
isotropic in the two directions broadside to the element. If we add ~6
dB from ground reflection gain, we get 8 dB gain over isotropic, but
this is ONLY for a specific TOA which is determined by the antenna's
height above ground. Of course a good Yagi will typically have 25-30
dB Front to Rear, so its backward lobe has very little of the total
energy (far less than 50%).

Bottom line to all of this is that your antenna's height above ground
has the primary influence on TOA. The only other way to "steer" the
vertical lobe is to mount your antenna on a motorized tower (unless you
go to vertically stacked elements and phasing).

Put your single antenna at 120' and the vertical pattern will be
centered on about 9 degrees (assuming flat terrain).

73 & GL!

Bill W4ZV

P.S. Here are some results using HFTA for my 10 meter 3-stack:

http://users.vnet.net/btippett/terrain_&_toas.htm

Aren't you comparing kinetic versus potential without thought
to energy conservation
Regards
Art

Cecil Moore wrote:
Owen Duffy wrote:
How can there be rational discussion of principles when some people
must invent their own meaning for terms that have well defined
conventional meaning?

How about "power", Owen. Some physicists say that a
Poynting vector contains no power until some work
is done - that if an EM wave in free space never
encounters anything to which to transfer its energy,
its ExH watts are not power.

My question is: If an EM wave's ExH watts are not
power, what are those watts called? i.e. the units
of power are watts, but if in some cases, watts are
not power, what are they?
--
73, Cecil http://www.w5dxp.com