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Sci.Electronics.Basics -> 50 ohm load
There are 28 messages in this thread.
You are currently looking at messages 20 to 28.
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Author: Bob MyersDate: 13:34 31-07-07
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<robin.pain@googlemail.com> wrote in message
news:1185861780.499514.320000@57g2000hsv.googlegroups.com...
> You have just contradicted yourself. In line one you say "Free space
> had nothing to do with this" and then in lines 9~10 you say "...in
> free space is around 73 ohms..."
You need to work a bit on your reading comprehension. Saying:
"The feedpoint impedance of a dipole in free space is 73 ohms"
is a very, very different thing than saying that the impedance of
free space itself is anywhere near that number, which was the original
claim.
Bob M.
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Author: Rich GriseDate: 14:04 31-07-07
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On Tue, 31 Jul 2007 11:34:32 -0600, Bob Myers wrote:
> <robin.pain@googlemail.com> wrote in message
> news:1185861780.499514.320000@57g2000hsv.googlegroups.com...
>> You have just contradicted yourself. In line one you say "Free space had
>> nothing to do with this" and then in lines 9~10 you say "...in free
>> space is around 73 ohms..."
>
> You need to work a bit on your reading comprehension. Saying:
>
> "The feedpoint impedance of a dipole in free space is 73 ohms"
>
> is a very, very different thing than saying that the impedance of free
> space itself is anywhere near that number, which was the original claim.
>
377 Ohms:
http://whatis.techtarget.com/definition/0,,sid9_gci845268,00.html
A waveguide feedhorn is an impedance transformer. :-)
And, yes, "a dipole in freespace" is a lot different from freespace
itself. :-)
Cheers!
Rich
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On 31 Jul, 19:04, Rich Grise <r...@example.net> wrote:
> On Tue, 31 Jul 2007 11:34:32 -0600, Bob Myers wrote:
> > <robin.p...@googlemail.com> wrote in message
> >news:1185861780.499514.320000@57g2000hsv.googlegroups.com...
> >> You have just contradicted yourself. In line one you say "Free space
had
> >> nothing to do with this" and then in lines 9~10 you say "...in
free
> >> space is around 73 ohms..."
>
> > You need to work a bit on your reading comprehension. Saying:
>
> > "The feedpoint impedance of a dipole in free space is 73 ohms"
>
> > is a very, very different thing than saying that the impedance of free
> > space itself is anywhere near that number, which was the original claim.
>
> 377 Ohms:http://whatis.techtarget.com/definition/0,,sid9_gci845268,00.html
>
> A waveguide feedhorn is an impedance transformer. :-)
>
> And, yes, "a dipole in freespace" is a lot different from freespace
> itself. :-)
>
> Cheers!
> Rich
73 and 377 seem close together to me in the vast expanse of modern
electronic ranges but this might be, as you say, irrelevant; it might
be just as easy to match a Z of 1 to a Z of 10,000 antenna wise as it
is to match Zs of 1 : 5.16
***********************************************************************
The matching of antenna to free space is the astonishing thing. The
other poster, the touchy one, said that it is empty, there is no
medium for it to travel through.
So this vacuum has characteristics that are material - I suppose the
Uncertainty Principle is the answer in that there is no such thing as
empty.
Robin
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Author: Bob MyersDate: 15:33 31-07-07
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<robin.pain@googlemail.com> wrote in message
news:1185909034.660449.303920@o61g2000hsh.googlegroups.com...
> The matching of antenna to free space is the astonishing thing. The
> other poster, the touchy one, said that it is empty, there is no
> medium for it to travel through.
>
> So this vacuum has characteristics that are material - I suppose the
> Uncertainty Principle is the answer in that there is no such thing as
> empty.
That the vacuum has physical characteristics isn't all
that surprising - one example, and one that is intimately
tied to this whole discussion (although it may not be that
obvious at first glance) is that it is these very same
characteristics of "free space" (a vacuum) which determine
the speed of light (and in fact, any electromagnetic wave)
through it.
There is no conflict in saying that "the vacuum" has no material
content (that it is empty, devoid of any material content) while
at the same time saying that it has characteristics which affect
the behavior of the physical world. That there is no "medium"
required for EM propagation refers to the old notion that there
had to be SOMETHING physical ("the ether") which carried
these waves, an idea that was thoroughly discredited by the
famous Michelson-Morley experiment of 1887. The hypothetical
"ether" through which light and other EM waves was believed to
have travelled would have constituted an absolute frame of
reference with respect to the rest of the universe, and this was
shown not to be the case (and later on, Einstein showed that there
could be no such "privileged" frame).
Bob M.
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Author: Rich GriseDate: 20:54 31-07-07
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On Tue, 31 Jul 2007 12:10:34 -0700, robin.pain wrote:
> 73 and 377 seem close together to me in the vast expanse of modern
> electronic ranges but this might be, as you say, irrelevant; it might be
> just as easy to match a Z of 1 to a Z of 10,000 antenna wise as it is to
> match Zs of 1 : 5.16
It would be very helpful for you to read a book or two before making
speculations like this.
Good Luck!
Rich
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Author: Don BoweyDate: 22:51 31-07-07
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On 7/31/07 12:33 PM, in article f8o2q2$pho$1@usenet01.boi.hp.com, "Bob
Myers" <nospamplease@address.invalid> wrote:
>
> <robin.pain@googlemail.com> wrote in message
> news:1185909034.660449.303920@o61g2000hsh.googlegroups.com...
>
>> The matching of antenna to free space is the astonishing thing. The
>> other poster, the touchy one, said that it is empty, there is no
>> medium for it to travel through.
>>
>> So this vacuum has characteristics that are material - I suppose the
>> Uncertainty Principle is the answer in that there is no such thing as
>> empty.
>
> That the vacuum has physical characteristics isn't all
> that surprising - one example, and one that is intimately
> tied to this whole discussion (although it may not be that
> obvious at first glance) is that it is these very same
> characteristics of "free space" (a vacuum) which determine
> the speed of light (and in fact, any electromagnetic wave)
> through it.
>
> There is no conflict in saying that "the vacuum" has no material
> content (that it is empty, devoid of any material content) while
> at the same time saying that it has characteristics which affect
> the behavior of the physical world. That there is no "medium"
> required for EM propagation refers to the old notion that there
> had to be SOMETHING physical ("the ether") which carried
> these waves, an idea that was thoroughly discredited by the
> famous Michelson-Morley experiment of 1887. The hypothetical
> "ether" through which light and other EM waves was believed to
> have travelled would have constituted an absolute frame of
> reference with respect to the rest of the universe, and this was
> shown not to be the case (and later on, Einstein showed that there
> could be no such "privileged" frame).
>
> Bob M.
>
>
Drat! I just started the new Harry Potter book, and you stir up the need to
do some lengthy research. If there is no (nada, zilch, NONE) "privileged"
frame, how can the speed of light be constant?
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On 1 Aug, 01:54, Rich Grise <r...@example.net> wrote:
> On Tue, 31 Jul 2007 12:10:34 -0700, robin.pain wrote:
> > 73 and 377 seem close together to me in the vast expanse of modern
> > electronic ranges but this might be, as you say, irrelevant; it might be
> > just as easy to match a Z of 1 to a Z of 10,000 antenna wise as it is to
> > match Zs of 1 : 5.16
>
> It would be very helpful for you to read a book or two before making
> speculations like this.
>
> Good Luck!
> Rich
That's just a ploy on your part to keep me occupied and not posting
here: well maybe you are right because right now I'm into, and can
recommend, Churchill's "History of the English Speaking People"
Have a nice day
Robin
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Author: Bob MyersDate: 13:40 01-08-07
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"Don Bowey" <dbowey@comcast.net> wrote in message
news:C2D54334.7215A%dbowey@comcast.net...
> Drat! I just started the new Harry Potter book, and you stir up the need
> to
> do some lengthy research. If there is no (nada, zilch, NONE)
"privileged"
> frame, how can the speed of light be constant?
That's sorta the whole point (and what led Einstein to his
conclusion in the first place - the assumption that ALL observers
MUST be able to see the same value for the "speed of light").
What "privileged frame" means here is the notion of an
"absolute" frame against which all can be measured. The
supposed "ether" would have constituted such a frame -
a physical medium against which the speed of light could
at all times (and in all places) be measured. Michelson-
Morley did away with the ether, and later Einstein did away
with the notion that there was such an absolute frame of
reference in the first place. If you start out with the assumption
that EVERYONE, regardless of where they are or their own
velocity, must see the speed of light in a vacuum as the same
value, you come to the unavoidable conclusion that a lot
of the things we like to think of as stable and absolute
(distance, time, mass) in fact vary according to the frame
of reference of the observer in question - these things
are "relative" to that particular observer's point of view,
hence "theory of relativity."
Einstein got there via a "thought experiment" that was
roughly of this form: suppose I am riding on some sort of
vehicle that is travelling very close to the speed of light.
I have a flashlight, and I turn it on (you can try thinking
about this with the flashlight aimed in the direction of
travel, in the opposite direction, or to the side - it's fun
no matter how you look at it!). What do I see happen?
And if you're standing outside my vehicle, watching it
go past - and you can look in the windows as it does -
what do YOU see?
Bob M.
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