Re: basic question about light


"Randy Poe" <poespam-trap@xxxxxxxxx> wrote in message news:1171381004.133953.226180@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 13, 3:12 am, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Randy Poe" <poespam-t...@xxxxxxxxx> wrote in messagenews:1171342968.888633.224510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx

You will not find any reference where gain of an antenna
is a negative number.

No,
"Radiation Angle: It has been generally accepted that beamwidth is the angle between the two points (on the same plane) at which the radiation falls to "half power" i.e. 3dB below the point of maximum radiation. "
http://www.marcspages.co.uk/tech/antgain.htm
No, your citation.

But

No, did you snip something to say?
Oh, here it is...

"Randy Poe" <poespam-trap@xxxxxxxxx> wrote in message news:1171342968.888633.224510@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 12, 6:08 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Randy Poe" <poespam-t...@xxxxxxxxx> wrote in messagenews:1171296261.837480.275650@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 11, 9:27 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Randy Poe" <poespam-t...@xxxxxxxxx> wrote in messagenews:1171240756.771067.87350@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Feb 11, 2:24 pm, The Ghost In The Machine
<e...@xxxxxxxxxxxxxxxxxxxxxxx> wrote:
In sci.physics, Randy Poe
<poespam-t...@xxxxxxxxx>
wrote
on 11 Feb 2007 08:59:58 -0800
<1171213198.652662.133...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>:

On Feb 10, 9:32 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:
"Timo A. Nieminen" <t...@xxxxxxxxxxxxxxxxx> wrote in messagenews:Pine.WNT.4.64.0702110615050.1280@xxxxxxxxxxxx

On Sat, 10 Feb 2007, Androcles wrote:

"Timo A. Nieminen" <t...@xxxxxxxxxxxxxxxxx> wrote:
On Fri, 9 Feb 2007, Randy Poe wrote:

On Feb 8, 5:24 pm, "Androcles" <Engin...@xxxxxxxxxxxxxxxxxxxxxx>
wrote:

Are TV signals absorbed by aluminium molecules in the antenna?

Biological and man-made systems use different strategies. Visual
pigments are not conductors. Their electrons are bound to them,
not free as in an antenna.

That's half the story, the bio-half. There's more to be said on the other
half, too.

Ideally, the antenna doesn't absorb _any_ of the signal

Hahahaha!
By Queensland reasoning, ideally the eye doesn't absorb _any_ sunlight.
Dream on.

Oh all-wise and mighty "electronic engineer, professionaly", how much of
the signal is absorbed in an ideal antenna?

All of it.
Someday parabolic reflectors will come to the Outback.

So a 1 m parabolic antenna absorbs all the energy transmitted, and
so does a 10 m parabolic antenna?

Why ever build a big antenna then, if a little one absorbs all of
the available energy?

The bigger an antenna, the more available energy, and
presumably the easier to detect and/or amplify.

Take, for example, a 50 kW radiotransmitter tower,
10 km away. Ignoring such issues as ground absorption
and rereflection, one is looking at a sphere with 10 km
radius; the total area of that sphere is about 1257 km^2.
A 1 m diameter parabolic antenna will have an intercept
area of .7854 m^2, and, assuming perfect reflection, will
gather in all of about 31.25 microwatts. A 10m diameter
parabolic antenna will get 3.125 milliwatts of energy.

Presumably mismatching/overloading the amplifier is
an issue here as well. I'm also not exactly sure what
intercepts the reflected energy from the dish proper,
though suspect it's a simple quarterwave dipole, at least
for consumer units. Presumably, some of the energy is
reflected back through the focus of the antenna. I can't
say I know how much.

I'd say all of the energy from that tower is intercepted,
though not by that particular antenna; various things get
a share of that 50 kW -- and those things could be billions
of lightyears away.

And why do antenna designers believe that big antennas have
higher gain than little ones? What could that gain be due to?

I frankly don't think "gain" is the operative term here, though
I'll admit I'd be hard-pressed to find a better one apart from
the rather unwieldly "intercepted power".

But actually "gain" is the operative word in antenna design.

The lay word you really need is 'loss', but technically 'gain' is fine
as long as the dB number is negative.

No, gain is positive.

No, loss is negative.

Loss is negative. Gain is positive.

No, loss is negative, gain is positive.
No, do you always agree with me by saying 'no' first?
No, you are easily confused, aren't you?
No, that's what makes you a total fuckhead.


What makes it positive is what the power is
being compared to.

No, what makes it negative is what the power is being compared to.

The power it is being compared to is the power received via an
isotropic antenna.

No, that's what makes it negative.
No, an ideal antenna is not omnidirectional.


I could quote you engineering websites and books. In fact I have
on this subject in the past. But you dismiss actual references
as "word soup" and "loads of crap".

No, I don't give a flying *** what you can quote, you are an idiot.

But have fun trying to make sense of the Friis equation if you
use negative gains.

No, I don't use negative gains, I use positive losses.
No, an amplifier has gain, the best an antenna can do is pass on all the power.
No, so antennae have loss.
No, decelleration is negative acceleration, loss is negative gain.



Putting a high-gain receive antenna on your
radio will give you more power in the receiver than putting a low-gain
antenna there.

No, putting a high-loss receive antenna on your
radio will give you less power in the receiver than putting a low-loss
antenna there.



You've been linked to the Friis equation before.
http://en.wikipedia.org/wiki/Friis_transmission_equation

The gains there are positive.

"High gain" is a GOOD thing. In your terminology, a "high gain" would
be a "high loss". Loss is bad.

How do I obtain the dB gain/loss of cables and antennas?
A -10 dB loss reduces power to one tenth, while a +10 dB gain increase power ten times.

Yes,

No, YIPPEE! Blind Poe said "yes".
No, you are a fuckhead, an ideal antenna has zero loss. No antenna has gain.
No, the
****** lay ********
word you really need is 'loss', but technically 'gain' is fine
as long as the dB number is negative.



http://expertanswercenter.techtarget.com/eac/knowledgebaseAnswer/0,29...

Ain't no way an antenna can increase power. The best gain you'll get
is a gain of 1.

Antenna gain is relative to omnidirectional.

No antenna has gain, it cannot deliver more power than is recieved.

That's not what antenna gain means.

No, there is no such animal as antenna gain, antennae can only
lose signal.



http://www.marcspages.co.uk/tech/antgain.htm
"gain has a positive value"
No, "It is known as dBi and represents the gain of an antenna with respect to an imaginary isotropic antenna "
No, 'imaginary', Poe.
No, we are discussing an 'ideal' antenna, which is an imaginary antenna.
No, "Ideally, the antenna doesn't absorb _any_ of the signal" - Nieminen the Queensland fuckhead.



http://www.atis.org/tg2k/_antenna_gain.html

http://k9erg.tripod.com/theory.htm
"The gain of a dipole is +2.14 dB"

http://en.wikipedia.org/wiki/Parabolic_antenna
"Applying the formula to just one of the 25-meter-diameter VLA
antennas shown in the illustration for a wavelength of 21 cm
(1.42 GHz, a common radio astronomy frequency) yields an
approximate maximum gain of 140,000 times or about
50 dBi (decibels above the isotropic level)."

You will not find any reference where gain of an antenna
is a negative number.

No,
"Radiation Angle: It has been generally accepted that beamwidth is the angle between the two points (on the same plane) at which the radiation falls to "half power" i.e. 3dB below the point of maximum radiation. "
http://www.marcspages.co.uk/tech/antgain.htm
No, your citation.


No, 'below' doesn't mean negative, does it, Blind Poe?
No, 'half power' is greater than full power, isn't it, Blind Fuckhead Poe?
No, it turns out to be rather easy to find a reference where the gain of an
ideal antenna is a negative number and the loss is a positive number,
just turn it off axis.



You will not find any reference defining
gain the way you want to define it.

No, I just did in your citation.

I invite you to try.

No, the gain is -3dB when the ideal antenna is rotated to the second point.
No, 'below' is not a technical term.
No, the technical term is a gain of -3dB.

No, the lay word you really need is 'loss', but technically 'gain' is fine
as long as the dB number is negative.
No, where have I said that before?


But you don't do engineering or physics by reference. You
do it "making it up and dismissing what the handbooks say
as a 'load of crap'".

No, I don't do engineering by physics papers or listening to loads
of Poe crap, I'm too sensible for that.


.

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