On 11/1/2014 5:31 PM, wrote:
rickman wrote:
On 11/1/2014 1:03 PM, wrote:
gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ...

An antenna is an antenna.

Deep thoughts...


A wave is launched, and radiates SOME of the power, and suffers
both I2R losses and dielectric and permeability losses associated
with creating and collapsing the near field.

Nope, voltage is applied to an antenna causing currents to be created
which in turn cause an electromagnetic field to be created.

As antennas are made of real materials they have a resistance and the
current through that resistance leads to losses.

I thought there were *real* materials with no resistance. Isn't that
what a superconductor is?

Well, to be pendatic, there are no real materials with zero resistance
that can be used to build antennas.

Why can't you build an antenna with a superconductor?


As all the current existing superconductors require a bunch of supporting
equipment to keep them cold, they can't be used for antennas.

Really? What is the problem? There are super conductors at liquid
nitrogen temperatures and you can have that sitting in a flask on your
desk. Why couldn't that cool an antenna? Once you remove the I*R
losses, you don't even have to worry about the radiated power heating
the N2.

I think you are confusing need with practicality. There is nothing to
stop you from making a superconducting antenna. There just isn't a need
for it unless you live in Gareth's world. Hmmm... wasn't that a movie?
Gareth's World?


If room temperature superconductors are ever invented...

However, those are like a cure for the common cold, practical fusion
power, and peace in the Middle East, all just around the corner for
the past half century or so.

I've never heard anyone say either a cure for the common cold or fusion
was "around" the corner. I've never heard anyone say at all that peace
is expected in the middle east.

I believe there are rather cold temperatures in space. A
superconducting antenna could be used there with *no* supporting
"apparatus".

--

Rick

rickman wrote:
On 11/1/2014 5:31 PM, wrote:
rickman wrote:
On 11/1/2014 1:03 PM, wrote:
gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ...

An antenna is an antenna.

Deep thoughts...


A wave is launched, and radiates SOME of the power, and suffers
both I2R losses and dielectric and permeability losses associated
with creating and collapsing the near field.

Nope, voltage is applied to an antenna causing currents to be created
which in turn cause an electromagnetic field to be created.

As antennas are made of real materials they have a resistance and the
current through that resistance leads to losses.

I thought there were *real* materials with no resistance. Isn't that
what a superconductor is?

Well, to be pendatic, there are no real materials with zero resistance
that can be used to build antennas.

Why can't you build an antenna with a superconductor?


As all the current existing superconductors require a bunch of supporting
equipment to keep them cold, they can't be used for antennas.

Really? What is the problem? There are super conductors at liquid
nitrogen temperatures and you can have that sitting in a flask on your
desk. Why couldn't that cool an antenna? Once you remove the I*R
losses, you don't even have to worry about the radiated power heating
the N2.

If one were realy determined to do it, one could build the antenna
in a non-metalic container of some sort and keep the container filled
with LN2.

I think you are confusing need with practicality. There is nothing to
stop you from making a superconducting antenna. There just isn't a need
for it unless you live in Gareth's world. Hmmm... wasn't that a movie?
Gareth's World?

It is not need versus practicality, it is practicality period.

If room temperature superconductors are ever invented...

However, those are like a cure for the common cold, practical fusion
power, and peace in the Middle East, all just around the corner for
the past half century or so.

I've never heard anyone say either a cure for the common cold or fusion
was "around" the corner. I've never heard anyone say at all that peace
is expected in the middle east.

You must not be very old then...

I believe there are rather cold temperatures in space. A
superconducting antenna could be used there with *no* supporting
"apparatus".

You mean other than the shade screen?

You do understand two big problems with space stuff is how to get rid of
any generated heat and Solar heating?

In any case, why?

I^2R losses only become significant in very small antennas and there is
all the space you could ask for in space to build an antenna.


--
Jim Pennino

On Sat, 01 Nov 2014 18:47:32 -0400, rickman wrote:

I think you are confusing need with practicality. There is nothing to
stop you from making a superconducting antenna. There just isn't a need
for it unless you live in Gareth's world. Hmmm... wasn't that a movie?
Gareth's World?
(...)
I believe there are rather cold temperatures in space. A
superconducting antenna could be used there with *no* supporting
"apparatus".

You don't need to go to outer space to see cryogenic radios in
operation.

Superconducting radio frequency
http://en.wikipedia.org/wiki/Superconducting_radio_frequency

In a past project, I worked with cryogenic duplexers and receiver
front ends for cellular service. My part had nothing to do with the
superconducting components, but I got to watch them perform. Filters
with nearly vertical skirts, sky high filter shape factors, zero loss,
near zero noise figu
http://www.suptech.com/wireless_overview_n.php
http://www.suptech.com/pdf_products/cryogenic_receiver_front_end.pdf
http://www.suptech.com/pdf_products/SuperLink_850_G3AB.pdf
Where cryogenic front ends worked best are in installation without
towers, where the coax cable losses were less, and the cryo unit can
be located in a nearby rooftop shelter. These tend to be located in
urban jungles, where signals are traditionally weak, and handset
density rather high.

At the same time, TMA (tower mounted amp) technology appeared, which
provided many of the benefits of cryogenic receiver front ends, but
without the complexity, power consumption, and cost of the cooling
components:
http://en.wikipedia.org/wiki/Tower_Mounted_Amplifier
https://www.google.com/search?q=tower+mounted+amplifier&tbm=isch
http://www.commscope.com/catalog/wireless/2147486004/product.aspx?id=162&sortExp=Name&nrp=100

Also, note that spacecraft all have some form of temperature control
where the electronics do NOT operate at cryogenic temperatures:
http://en.wikipedia.org/wiki/Spacecraft_thermal_control




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

rickman wrote in :

I believe there are rather cold temperatures in space. A
superconducting antenna could be used there with *no* supporting
"apparatus".


There's still such a thing as radiation resistance, I think, so it wouldn't
stay cold even there. Given the size of a body, there's a limit to how fast
it can get rid of heat at a given temperature.. I don't know the proper
terminology for it though. Anyway, at low tenperature, the rate it can
radiate heat is low, so it will quickly warm up out of low-temp
superconducting state.

wrote in message ...

gareth wrote:
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ...

An antenna is an antenna.

A wave is launched, and radiates SOME of the power, and suffers
both I2R losses and dielectric and permeability losses associated
with creating and collapsing the near field.

Nope, voltage is applied to an antenna causing currents to be created
which in turn cause an electromagnetic field to be created.

As antennas are made of real materials they have a resistance and the
current through that resistance leads to losses.

However, in the real world most antennas have an impedance in the tens
of Ohms while the resistance is in milliohms, so normally the losses
are trivial compared to the radiation.

At first, there is no standing wave, until the wave reaches the point of
reflection
in the antenna and heads back the way it has come (because not all has
been
radiated*****)
On the way back, it againn suffers the losses described above, as well as
radiating a
bit more.

Pure nonsense.

It then reaches the other end and suffers further reflections ad
infinitum.

Pure nonsense.

An interesting conclusion is, therefore, that the I2R losses are repeated,
each tiome with a smaller loss, as the wave decrements.

A nonsense conclusion based on a nonsense assumption.

***** Without the remnants of non-radiated power, there could NOT be
a standing wave!

Sigh.

^^^^^^^^^^^
I was going to point out to Gareth that he is describing behavior in an
antenna system, not an antenna.

But, I'm done now. No more.

Wayne wrote:

snip

I was going to point out to Gareth that he is describing behavior in an
antenna system, not an antenna.

I doubt he will EVER understand the difference.

But, I'm done now. No more.

It does become tiresome correcting the same nonsense over and over again.

--
Jim Pennino

On 11/1/2014 8:18 PM, wrote:
Wayne wrote:

snip

I was going to point out to Gareth that he is describing behavior in an
antenna system, not an antenna.

I doubt he will EVER understand the difference.

But, I'm done now. No more.

It does become tiresome correcting the same nonsense over and over again.

Then there is no need at all to reply, no?

--

Rick

rickman wrote:
On 11/1/2014 8:18 PM, wrote:
Wayne wrote:

snip

I was going to point out to Gareth that he is describing behavior in an
antenna system, not an antenna.

I doubt he will EVER understand the difference.

But, I'm done now. No more.

It does become tiresome correcting the same nonsense over and over again.

Then there is no need at all to reply, no?

Other than to prevent a casual reader from thinking his nonsense is
reality, not really.

Well, that and I really have a thing about deflating long winded gas
bags.

--
Jim Pennino

"gareth" wrote in message
...
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ...

A wave is launched, and radiates SOME of the power, and suffers
both I2R losses and dielectric and permeability losses associated
with creating and collapsing the near field.

Of course, it goes without saying that the wave was already travelling up
the feeder
and it diffracts along the elements of the antenna, rather than being
launched from
the feedpoint!

gareth wrote:
"gareth" wrote in message
...
Ignoring, for the moment, travelling wave antenna, and restricting
discussion to standing wave antennae ...

A wave is launched, and radiates SOME of the power, and suffers
both I2R losses and dielectric and permeability losses associated
with creating and collapsing the near field.

Of course, it goes without saying that the wave was already travelling up
the feeder
and it diffracts along the elements of the antenna, rather than being
launched from
the feedpoint!

Nope; there is an electric field in a feed line (other than wave guide)
but no electromagnetic field.

As a problem for the student, how big would a wave guide have to be to
be able to transfer 7 Mhz?

About the only antenaa where a "wave is launched" is a dielectric lens
antenna with a wave guide feed.

Of course, at the other end of the wave guide is an antenna to which
voltage is applied, which causes current flow in the antenna, which
causes an electromagnetic field to be created in the wave guide which
then flows to the antenna.


--
Jim Pennino