wrote:
art wrote:
On 10 May, 14:41, (Richard Harrison) wrote:
Art wrote:

"For my interest, what is the unit that must be used for front to back
ratio of a directive antenna?"

I must be an idiot for venturing an answer, but ratios can be just
numbers, but numbers have origins. If radiated power in one direction is
twice that in another (reference), we can say it has a directive gain of
two or we can say it has a 3 dB gain. Front to back ratios have the same
origins and units. For legitimacy, Terman says on page 871 of his 1955
opus:
"The directive gain can be expressed either as a power ratio, or in
terms of the equivalent number of decibels.

Best regards, Richard Harrison, KB5WZI

So it is now the norm not to cancel units of measurement in physics?
Woe is me. Free speech takes on a new meaning for some but not
acceptable from others meaning a term for a formula can now be called
a ratio with units of one's choice. Still, this is amateur radio after
all, it does not have to follow professional standards as most was
learned in the CB era

Example:

Forward gain = 12db
Reverse gain = 2db

Front to back ratio = 12db/2db = 6; no units as they cancel.

5th grade mathematics.

I've been reading Cecil's posts too long and thought I'd play some
gotcha games, but my conscience got the better of me.

Since db is logarithmic, you subtract to divide, so it would
be:

12db - 2db = 10db

If using say power density or field strength in linear units, then
you divide, the units cancel, and you get a unitless number.


--
Jim Pennino

Remove .spam.sux to reply.

On 10 May, 18:09, "Frank's"
wrote:
I am aware that the impedance of a particular
atmosphere is 377 ohms but that is certainly not a ratio.

From:http://whatis.techtarget.com/definit...845268,00.html

Frank, you got my attention when you pointed to the above link.
I read it a few times and 377 ohms was refered to as Zo. I can't find
any reference
that states Zo is a ratio. Did you intend to point to another link
that specifically points
to Zo is a ratio? Surely you are not following in the steps of others
where anything can be written
right or wrong as long as it creats an augument or distress? You
disapoint me!
Some in this group are already thinking it is legal for a ratio to
have units assigned
because of the inference that the link say's it's so which is an
untruth and
you are perpetuating the spread of untruths. This is similar to
another untruth
that is being perpetuated with respect to photons just because one
person
it be so stated. It is getting to the point that if you read it on the
net don't believe it

unless it can be verified.

I think you are confusing a posting by Cecil. Anyway, quoting
from "Engineering Electromagnetics" by Nathan Ida, 2nd ed. p 743:
"....the reference field is E (an arbitrary choice used in
electromagnetics as a convention). Thus we define the ratio between
Ex(z) and Hy(z) as eta = Ex(z)/Ey(z) = ...... sqrt(mu/epsilon) [ohms]
This quantity is an impedance because the electric field intensity is
given in [V/m] and the magnetic field intensity is given in [A/m].
The quantity eta is called the intrinsic impedance or wave impedance
of the material.....".

Frank

O.K. I will go with the majority and bedamned to those who oppose us.
I now know what the new or modern mathematics is all about and
called for by educationists. I suppose the next generation will be
completely at home with these new conventions unlike the mixture
that we presently have. Shame that they didn't introduce modern math
some 50 years ago which would have shortened this thread by 90%.
Regards
Art

On 10 May, 13:58, "Frank's"
wrote:
"Cecil Moore" wrote in message

t...





art wrote:
I am aware that the impedance of a particular
atmosphere is 377 ohms but that is certainly not a ratio.

From:http://whatis.techtarget.com/definit...845268,00.html

Mathematically, the Zo of free space is equal to the square root of the
ratio of the permeability of free space (µo) in henrys per meter (H/m) to
the permittivity of free space (o) in farads per meter (F/m):

Zo = (µo/o)1/2

= [(1.257 x 10-6 H/m)/(8.85 x 10-12 F/m)]1/2

= 377 ohms (approximately)

The exact value of the Zo of free space is 120 pi ohms, where pi is the
ratio of the circumference of a circle to its diameter.
--
73, Cecil, w5dxp.com

Also the ratio of E/H. [(V/m)/(A/m)] = [ohms].

Frank- Hide quoted text -

- Show quoted text -

Wow, this is exciting. There is a whole new World out there
and we have books that say's it is so. This modern mathematics
is going to make thing a lot easier for all book readers.
Art

I think you are confusing a posting by Cecil. Anyway, quoting
from "Engineering Electromagnetics" by Nathan Ida, 2nd ed. p 743:
"....the reference field is E (an arbitrary choice used in
electromagnetics as a convention). Thus we define the ratio between
Ex(z) and Hy(z) as eta = Ex(z)/Ey(z) = ...... sqrt(mu/epsilon) [ohms]
This quantity is an impedance because the electric field intensity is
given in [V/m] and the magnetic field intensity is given in [A/m].
The quantity eta is called the intrinsic impedance or wave impedance
of the material.....".

Frank

O.K. I will go with the majority and bedamned to those who oppose us.
I now know what the new or modern mathematics is all about and
called for by educationists. I suppose the next generation will be
completely at home with these new conventions unlike the mixture
that we presently have. Shame that they didn't introduce modern math
some 50 years ago which would have shortened this thread by 90%.
Regards
Art

Checking an older textbook: "Electromagnetic Theory"
by Julius Adams Stratton, published in 1941, pp 283,
284: "...... the intrinsic impedance of the medium for plane waves is
defined by Schelkunoff* as the quantity Zo = sqrt(Z/Y) ....... In free
space this impedance reduces to Zo = sqrt(mu/epsilon) = 376.6 ohms.

*Schelkunoff, Bell System Tech. J., 17, 17, January, 1938.

Where mu and epsilon are defined by Cecil in an earlier posting.

Frank

On 10 May 2007 18:28:38 -0700, art wrote:

Shame that they didn't introduce modern math
some 50 years ago which would have shortened this thread by 90%.

Hi Art,

You will have to go back nearly three times that many years, 1864 - to
Maxwell once again.
The quantity eta is called the intrinsic impedance or wave impedance
of the material.....".
120 * pi (roughly 377) Ohms is a fact of nature.

73's
Richard Clark, KB7QHC

On 10 May, 19:02, Richard Clark wrote:
On 10 May 2007 18:28:38 -0700, art wrote:

Shame that they didn't introduce modern math
some 50 years ago which would have shortened this thread by 90%.

Hi Art,

You will have to go back nearly three times that many years, 1864 - to
Maxwell once again. The quantity eta is called the intrinsic impedance or wave impedance
of the material.....".

120 * pi (roughly 377) Ohms is a fact of nature.

73's
Richard Clark, KB7QHC

Heh I am agreeing with you, 377 ohms is a ratio pure and simple.
I am now a member of the majority. I used to call 377 ohms an
impedance
but I am now am agreement with the majority, 377 ohms is a ratio.
If Maxwell is part of the majority how can I go wrong. Seems like the
blitz
got in the way of that jewel being passed on.
Art

On 10 May 2007 12:30:13 -0700, wrote:

Particels of what?

Hi Herbert,

(You asked this before to no answer, haven't you?) Electrons, by
Art's latest statement (although he suggested it with mock
acceptance). It may be something different tomorrow (like Protons).

This thread is turning into one of those fantasies of the Boy's
magazines of the 1950s: "Build a nuclear reactor on your kitchen
table!"

73's
Richard Clark, KB7QHC

On 10 May 2007 19:15:32 -0700, art wrote:

I used to call 377 ohms an
impedance

Hi Art,

All impedances are ratios. Nothing has changed since 1864.

73's
Richard Clark, KB7QHC

On 10 May, 18:57, "Frank's"
wrote:
I think you are confusing a posting by Cecil. Anyway, quoting
from "Engineering Electromagnetics" by Nathan Ida, 2nd ed. p 743:
"....the reference field is E (an arbitrary choice used in
electromagnetics as a convention). Thus we define the ratio between
Ex(z) and Hy(z) as eta = Ex(z)/Ey(z) = ...... sqrt(mu/epsilon) [ohms]
This quantity is an impedance because the electric field intensity is
given in [V/m] and the magnetic field intensity is given in [A/m].
The quantity eta is called the intrinsic impedance or wave impedance
of the material.....".

Frank

O.K. I will go with the majority and bedamned to those who oppose us.
I now know what the new or modern mathematics is all about and
called for by educationists. I suppose the next generation will be
completely at home with these new conventions unlike the mixture
that we presently have. Shame that they didn't introduce modern math
some 50 years ago which would have shortened this thread by 90%.
Regards
Art

Checking an older textbook: "Electromagnetic Theory"
by Julius Adams Stratton, published in 1941, pp 283,
284: "...... the intrinsic impedance of the medium for plane waves is
defined by Schelkunoff* as the quantity Zo = sqrt(Z/Y) ....... In free
space this impedance reduces to Zo = sqrt(mu/epsilon) = 376.6 ohms.

*Schelkunoff, Bell System Tech. J., 17, 17, January, 1938.

Where mu and epsilon are defined by Cecil in an earlier posting.

Frank- Hide quoted text -

- Show quoted text -

Jimminy cricket, Are you now saying that 377 ohms is an
impedance and not a ratio ? No wonder the threads are so long.
Can you pass this info on to those who declare it as a ratio
so I can decide with whome I declare allegance to? Harrison
and others read it in a book that 377 ohms was a ratio and
if it is in a book it must be reliable and this group is never in
error.
The correctness of this statement has the true efficiency of a yagi on
hold
because when properly matched losses are 50 % of that energy that
was coupled.
In a Gaussian array there is no coupling... whow what an achievement
the group is pointing out with respect to efficiency.
I am a happy camper.
Art

On 10 May, 19:25, Richard Clark wrote:
On 10 May 2007 19:15:32 -0700, art wrote:

I used to call 377 ohms an
impedance

Hi Art,

All impedances are ratios. Nothing has changed since 1864.

73's
Richard Clark, KB7QHC

Right on. I understood for once your posting now that you are
not including flim flam. If that is what you believe I am
comfortable in following suit.
Is this now the end of this thread?
Do we now have closure?