Horvath wrote in :

On Thu, 04 Sep 2003 13:20:03 GMT, "Flounder" wrote
this crap:

No, it's less attenuation in its normal mode of propagation. It has to do
with the decompression of the magnetosphere on the side of the earth away
from the sun..

Actually it's the ionosphere,

Almost all AM radio stations transmit in the vertical polarization, the
antenna beam launch angle is low, it's difficult to get skip.

Were we talking about commercial AM radio? I thought we were talking
about SSB.

You just never seem to be on the right page, do you?

Bertie

I seem to recall commercial advertisement for single mode fibres that
involved a graduated refractive index rather than extremely small diameter.
One thing is certain, until the amount of work involved with polishing the
ends is reduced, it will never replace copper wire for low cost or casual
applications.

"Flounder" wrote in message
ink.net...
Absolutely the same thing as modes in a fibre optic cable. Except cables
are
cylindrical (field solutions described by Bessel functions) and the
water-air geometry is described by some form of Hankel functions.

Single mode fibres are very thin. The thick cables have very many modes,
all
traveling with different phase velocities and distorting pulses over the
length of the cable. Single mode fibres propagate only one mode and the
pulse retains its shape over very long distances.

The fibre optic cables act as waveguides. If the diameter of the cable is
too small (about less than 1/2 wavelength) a wave will not propagate in
the
cable. If the diameter is greater than about 1/2 wavelength up to roughly
..6
wavelengths then the first mode propagates called the HE11 mode. A little
larger diameter propagates the HE11 and the TE01 modes. As you increase
the
diameter the number of modes increases. There's also degenerate modes,
hybrid modes, transverse electric and magnetic modes. It gets fairly
complex. There's a formula used to calculate the number of modes in big
fibres. This is all for stepped index fibres.

Fibre cables are clad to keep dust of the cable. The dust disturbs the
evanascent modes on the outside of the cable (kills the signal) just like
dirty prisms cause binoculars to work poorly.

Feel free to ask more questions, I can use the review.



"Donal" wrote in message
...

"Flounder" wrote in message
ink.net...
There's a layer of air on the surface of the water that has a
difference
in
temperature in the air above it. The permitivitty (index of
refraction)
of
the two layers of air are different. The difference is in the
thousandth
decimal place. Because of the difference in the permitivitty a radio
wave
striking the upper layer at or below the Brewster angle experiences
total
internal reflection. The wave becomes trapped between the water and
the
second air layer. Part of the wave does travel in the second layer, at
the
boundary. That is the evanescent wave. That is also the type of wave
that
allows your prism binoculars to work. The wave also travels at two
different
velocities in the two air layers.
So, looking at the transmitting antenna as an isotropic radiator at
150
MHz,
the layer height at 30 meters how many modes propagate on the sea
surface?


You call *that* an explanation??

BTW, these "modes" that you refer to, - are they in any way similiar to
the
"modes" in fibre optic transmission systems? They sound like they might
be.

If they are, I would be very interested is a *plain* English
explanation!
I really should know the difference between multi- and single-mode fibre
optics.

BTW this isn't a trick question. I'm genuinely interested.



Regards


Donal
--

Yeah Wally.... 40 nautical miles for a good VHF is possible.

CM

"Wally" wrote in message
...
| Bobsprit claims to have made a VHF transmission of over 40nm. Given that
his
| antenna height is about 50 feet, that would require, for a line of sight
| transmission, that the other antenna be about 800 - eight hundred - feet
| above the water.
|
| I believe that 40 miles is too close for skip, so could his transmission
| have a 'terrain following' effect in the sense that the sea might act as a
| ground plane?
|
| Would anyone care to comment on the veracity of Bobsprit's claim?
|
|
| --
| Wally
| www.makearatherlonglinkthattakesyounowhere.com
| Things are always clearer in the cold, post-upload light.
|
|
|

Yeah Wally.... 40 nautical miles for a good VHF is possible.

And STILL I get no apology from Wally who infered that I was lying.
For shame!

RB

"Bobsprit" wrote in message
...
| Yeah Wally.... 40 nautical miles for a good VHF is possible.
|
| And STILL I get no apology from Wally who infered that I was lying.
| For shame!

Hang on... I'll cut you a slice from my round of gouda to go with that
whine... err wine.

CM

Bobsprit wrote:
Yeah Wally.... 40 nautical miles for a good VHF is possible.

And STILL I get no apology from Wally who infered that I was lying.

If you think I inferred that you were lying, it would have been because the
evidence empirically presented would lead one to draw such an inference.
However, the word I believe you are attemptng to utilise is not 'infer', but
'imply'. To use 'infer' in place of 'imply' is slack.

I didn't apologise, because I made no such implication. I did question the
veracity of your claim, but did so with the qualification that I stand to be
corrected. This was clearly implied, and the inference thus readily
available to be drawn by the reader, by the title of the thread in which I
enquired into the veracity of your claim, namely, "Radio question" - this
very thread. I invite you to read the original post again. Furthermore, on
the matter of your attempting to troll for a butt-kiss, I responded to your
similar comment regarding this yesterday.

Happy now, battery boy?

Oh, when did you say your next trip is? Let me know - I'll keep my handheld
switched on. Hail me! Channel 9!


--
Wally
www.makearatherlonglinkthattakesyounowhere.com
Things are always clearer in the cold, post-upload light.

I did question the
veracity of your claim, but did so with the qualification that I stand to be
corrected.

Since Morris Cove is a specific distance and you sought clarification about VHF
range, the only alternative would have been that I was lying.
Therefore the inference was clear. You were wrong about VHF range and following
your challenging my claim, were alerted to this.
A good chap might say, "Sorry for doubting you."
Then again....

RB

Happy now, battery boy?

Yes. Happy that you were wrong and I was right.
But maybe you learned something about radio?
Maybe.

RB

Furthermore, on
the matter of your attempting to troll for a butt-kiss,

This is how you view a simple apology? I see.

RB

Yeah ... Gosh Already... it's not as if Bob ever lied about anything before.

CM

"Bobsprit" wrote in message
...
| I did question the
| veracity of your claim, but did so with the qualification that I stand to
be
| corrected.
|
| Since Morris Cove is a specific distance and you sought clarification
about VHF
| range, the only alternative would have been that I was lying.
| Therefore the inference was clear. You were wrong about VHF range and
following
| your challenging my claim, were alerted to this.
| A good chap might say, "Sorry for doubting you."
| Then again....
|
| RB