[rebel-builders] vhf radio

[bransom]

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions, whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places, at
least to be *sure* of being heard for urgent or serious matters is via ham?
-Ben/ 496R



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[Garry Wright]

Its really just a matter of frequency. VHF comm is 'line of sight'. At
VHF frequencies there is a little bit of diffraction at knife edges but
out on the prairies it is pure line of sight. There is a rare phenom
called 'sporadic E' that is a reflection off an atmospheric layer at
these frequencies, but it usually is very long range - hundreds of
miles, and not likely to enter our picture. Type of modulation does not
have much bearing on the issue of long distance propagation. It tends to
affect clarity more. The reason you don't hear guys announcing their
departure at distant places is they haven't got line of sight at that
altitude due to earth curvature.

Garry

bransom@dcsol.com wrote:

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions, whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places, at
least to be *sure* of being heard for urgent or serious matters is via ham?
-Ben/ 496R



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[Mike Kimball]

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at night.
I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions, whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places, at
least to be *sure* of being heard for urgent or serious matters is via ham?

-Ben/ 496R



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[Garry Wright]

Again its just frequency, not modulation that relates to ionispheric
conditions. The AM radio band is fairly low frequency 560kHz to 1600kHz
or so depending on where you are. It does bounce. It is true that
civilian aircraft transmissions are AM/VHF. They don't bounce generally.

Garry

Mike Kimball wrote:

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at night.
I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions, whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places, at
least to be *sure* of being heard for urgent or serious matters is via ham?

-Ben/ 496R



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[Mike Kimball]

Thanks Garry. Interesting. I think I've also heard that if you use a long
enough wavelength you could transmit through the earth. I think you would
need an incredibly long antenna though to pick up the signal. Don't
submarines use an extremely long antenna trailed behind for this kind of
transmission/reception while submerged?

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Garry
Wright
Sent: Sunday, October 14, 2007 3:08 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] vhf radio

Again its just frequency, not modulation that relates to ionispheric
conditions. The AM radio band is fairly low frequency 560kHz to 1600kHz
or so depending on where you are. It does bounce. It is true that
civilian aircraft transmissions are AM/VHF. They don't bounce generally.

Garry

Mike Kimball wrote:

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at

night.

I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions,

whatever

goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places,

at

least to be *sure* of being heard for urgent or serious matters is via

ham?

-Ben/ 496R



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[Garry Wright]

I have read that. The very low frequencies like 10 kHz will also
propagate and are not attenuated with depth below the sea's surface as
quickly as higher frequencies. Thus the use for submarine work.
Information capacity of such a carrier is pretty low though. You could
not carry a conversation on such a carrier frequency. Slow morse is
about all it will handle.

Garry

Mike Kimball wrote:

Thanks Garry. Interesting. I think I've also heard that if you use a long
enough wavelength you could transmit through the earth. I think you would
need an incredibly long antenna though to pick up the signal. Don't
submarines use an extremely long antenna trailed behind for this kind of
transmission/reception while submerged?

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Garry
Wright
Sent: Sunday, October 14, 2007 3:08 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] vhf radio

Again its just frequency, not modulation that relates to ionispheric
conditions. The AM radio band is fairly low frequency 560kHz to 1600kHz
or so depending on where you are. It does bounce. It is true that
civilian aircraft transmissions are AM/VHF. They don't bounce generally.

Garry

Mike Kimball wrote:

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at

night.

I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions,

whatever

goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places,

at

least to be *sure* of being heard for urgent or serious matters is via

ham?

-Ben/ 496R



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[Bill Maxwell]

It's not the modulation method, either AM, FM , SSB or whatever, that
determines skip, bounce or reflection from the ionosphere Mike, but the
frequency and therefore the wavelength being used. High Frequency
transmissions do it most reliably but Medium frequencies can do it,
especially at night when particular layers form in the ionosphere. Broadcast
stations in the AM band display this
well, with stations in SouthEast Asia being regularly heard at this location
in Australia.

VHF transmissions, such as those in the Airband, and UHF transmissions do
not reflect off the ionosphere but pass straight through and out to space,
which is how radio communication with satellites is possible. Similarly,
they travel in straight lines at all other angles, including down and
sidewise. They are therefore very much line of sight. The guy departing from
that distant runway cant be heard because he is still on the ground and
there is no line of sight to you. Once he gets airborne though, his
effective range increases with more line of sights opening up to him.

While not impacted by the ionosphere, VHF and UHF transmissions can
sometimes be impacted by a lower region, the troposphere, where the signals
can get trapped and re-directed between tropospheric layers, leading to the
phenomenon known as tropospheric ducting. We regularly encounter this here
in South Eastern Australia in Spring and early Summer, with signals in the 2
meter band, 144 to 148 MHz, being heard up to 1000 Kms away. That is very
close to the Airband.

The other phenomenon readily seen at VHF and UHF is the so-called knife-edge
refraction, where a signal can sometimes be heard on the other side of a
ridge when it is refracted downwards as it passes over the ridge. You can
demonstrate this by shining a torch side on to a knife blade and observing
the light that falls on the surface behind the blade.

There can be a number of reasons for somebody in the pattern with you being
hard to read, ranging through shielding of your antenna by your own airframe
to the strength of the other's nearby transmission simply overloading the
front end of your receiver and producing garbled signals.

Bill


----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Monday, October 15, 2007 8:18 AM
Subject: RE: [rebel-builders] vhf radio

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at
night.
I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions,
whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places,
at
least to be *sure* of being heard for urgent or serious matters is via
ham?

-Ben/ 496R



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[Bill Maxwell]

Would love to visit but Alaska from Tasmania is a long way .............
----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, October 16, 2007 8:09 AM
Subject: RE: [rebel-builders] vhf radio

It wasn't me reporting trouble hearing others in the pattern. It was Ben.
I have trouble hearing others no matter who it is or where they are.
Still
haven't figured out my radio noise problem. Sounds like you know a thing
or
two about RF. Care to visit Alaska anytime soon?

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Bill
Maxwell
Sent: Sunday, October 14, 2007 3:25 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] vhf radio

It's not the modulation method, either AM, FM , SSB or whatever, that
determines skip, bounce or reflection from the ionosphere Mike, but the
frequency and therefore the wavelength being used. High Frequency
transmissions do it most reliably but Medium frequencies can do it,
especially at night when particular layers form in the ionosphere.
Broadcast

stations in the AM band display this
well, with stations in SouthEast Asia being regularly heard at this
location

in Australia.

VHF transmissions, such as those in the Airband, and UHF transmissions do
not reflect off the ionosphere but pass straight through and out to space,
which is how radio communication with satellites is possible. Similarly,
they travel in straight lines at all other angles, including down and
sidewise. They are therefore very much line of sight. The guy departing
from

that distant runway cant be heard because he is still on the ground and
there is no line of sight to you. Once he gets airborne though, his
effective range increases with more line of sights opening up to him.

While not impacted by the ionosphere, VHF and UHF transmissions can
sometimes be impacted by a lower region, the troposphere, where the
signals
can get trapped and re-directed between tropospheric layers, leading to
the
phenomenon known as tropospheric ducting. We regularly encounter this here
in South Eastern Australia in Spring and early Summer, with signals in the
2

meter band, 144 to 148 MHz, being heard up to 1000 Kms away. That is very
close to the Airband.

The other phenomenon readily seen at VHF and UHF is the so-called
knife-edge

refraction, where a signal can sometimes be heard on the other side of a
ridge when it is refracted downwards as it passes over the ridge. You can
demonstrate this by shining a torch side on to a knife blade and observing
the light that falls on the surface behind the blade.

There can be a number of reasons for somebody in the pattern with you
being
hard to read, ranging through shielding of your antenna by your own
airframe

to the strength of the other's nearby transmission simply overloading the
front end of your receiver and producing garbled signals.

Bill


----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Monday, October 15, 2007 8:18 AM
Subject: RE: [rebel-builders] vhf radio

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at
night.
I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away
sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions,
whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm
just
making this up to suit my imagination, but I think about it every time
I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places,
at
least to be *sure* of being heard for urgent or serious matters is via
ham?

-Ben/ 496R



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[gleeso]

Tassie is even a long way from Australia. (sorry Bill, couldn't let
that go by)
Rebel 804 down under.




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[Rick Harper]

I hope you guys are coming to the SAAA "Escape to Cowra" Convention - this coming weekend !

Rick "Biggus" Harper
541R .... flying AGAIN
----- Original Message -----
From: gleeso
To: rebel-builders@dcsol.com
Sent: Tuesday, October 16, 2007 4:28 PM
Subject: Re: [rebel-builders] vhf radio


Tassie is even a long way from Australia. (sorry Bill, couldn't let
that go by)
Rebel 804 down under.




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[Bill Maxwell]

Now that's true but we will be glad of that come any invasion......?

Bill 756R

----- Original Message -----
From: "gleeso" <gleeso1@iprimus.com.au>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, October 16, 2007 4:28 PM
Subject: Re: [rebel-builders] vhf radio

Tassie is even a long way from Australia. (sorry Bill, couldn't let
that go by)
Rebel 804 down under.




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[Bill Maxwell]

'Fraid not Rick, cant make it. But wasn't Cowra the place to escape from?
----- Original Message -----
From: "Rick Harper" <rjwh@optusnet.com.au>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, October 16, 2007 4:33 PM
Subject: Re: [rebel-builders] vhf radio

I hope you guys are coming to the SAAA "Escape to Cowra" Convention -
this coming weekend !

Rick "Biggus" Harper
541R .... flying AGAIN
----- Original Message -----
From: gleeso
To: rebel-builders@dcsol.com
Sent: Tuesday, October 16, 2007 4:28 PM
Subject: Re: [rebel-builders] vhf radio


Tassie is even a long way from Australia. (sorry Bill, couldn't let
that go by)
Rebel 804 down under.




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[Mike Kimball]

It wasn't me reporting trouble hearing others in the pattern. It was Ben.
I have trouble hearing others no matter who it is or where they are. Still
haven't figured out my radio noise problem. Sounds like you know a thing or
two about RF. Care to visit Alaska anytime soon?

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of Bill
Maxwell
Sent: Sunday, October 14, 2007 3:25 PM
To: rebel-builders@dcsol.com
Subject: Re: [rebel-builders] vhf radio

It's not the modulation method, either AM, FM , SSB or whatever, that
determines skip, bounce or reflection from the ionosphere Mike, but the
frequency and therefore the wavelength being used. High Frequency
transmissions do it most reliably but Medium frequencies can do it,
especially at night when particular layers form in the ionosphere. Broadcast

stations in the AM band display this
well, with stations in SouthEast Asia being regularly heard at this location

in Australia.

VHF transmissions, such as those in the Airband, and UHF transmissions do
not reflect off the ionosphere but pass straight through and out to space,
which is how radio communication with satellites is possible. Similarly,
they travel in straight lines at all other angles, including down and
sidewise. They are therefore very much line of sight. The guy departing from

that distant runway cant be heard because he is still on the ground and
there is no line of sight to you. Once he gets airborne though, his
effective range increases with more line of sights opening up to him.

While not impacted by the ionosphere, VHF and UHF transmissions can
sometimes be impacted by a lower region, the troposphere, where the signals
can get trapped and re-directed between tropospheric layers, leading to the
phenomenon known as tropospheric ducting. We regularly encounter this here
in South Eastern Australia in Spring and early Summer, with signals in the 2

meter band, 144 to 148 MHz, being heard up to 1000 Kms away. That is very
close to the Airband.

The other phenomenon readily seen at VHF and UHF is the so-called knife-edge

refraction, where a signal can sometimes be heard on the other side of a
ridge when it is refracted downwards as it passes over the ridge. You can
demonstrate this by shining a torch side on to a knife blade and observing
the light that falls on the surface behind the blade.

There can be a number of reasons for somebody in the pattern with you being
hard to read, ranging through shielding of your antenna by your own airframe

to the strength of the other's nearby transmission simply overloading the
front end of your receiver and producing garbled signals.

Bill


----- Original Message -----
From: "Mike Kimball" <mkimball@gci.net>
To: <rebel-builders@dcsol.com>
Sent: Monday, October 15, 2007 8:18 AM
Subject: RE: [rebel-builders] vhf radio

I always heard that AM was the kind of signal that could bounce off the
ionosphere. I once picked up a Kansas station in California late at
night.
I've heard that late at night it's more likely to happen but I don't know
why. FM is known to be line of sight. I believe that civilian aircraft
transmissions are AM/VHF.

Mike

-----Original Message-----
From: mike.davis@dcsol.com [mailto:mike.davis@dcsol.com] On Behalf Of
bransom@dcsol.com
Sent: Sunday, October 14, 2007 11:29 AM
To: rebel-builders@dcsol.com
Subject: RE: [rebel-builders] vhf radio

I've always assumed the surprisingly clear reception from far away sources
was maybe due to skipping or reflection. With that, you'd get the direct
line plus the shallow angle reflected. With nearby transmissions,
whatever
goes up/down gets diffused or absorbed instead of skipped. Maybe I'm just
making this up to suit my imagination, but I think about it every time I'm
straining to hear who the heck is on my tail in the pattern and getting
interrupted by the crystal clear busy chatter at airports 60 miles away.
Another look at this is that you never hear those at distant airports
announcing 'taking runway 23 for departure' ...yet they are the same
distance as the surprisingly clear reception. No wave skipping and the
surrounding terrain is like Walter's mountains.

Isn't aircraft bands amplitude modulated? and therefore line of sight and
rather short? If wanting to transmit from mountains or far away places,
at
least to be *sure* of being heard for urgent or serious matters is via
ham?

-Ben/ 496R



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[Rick Harper]

Only if you were a "Nip" ... during WW2 !!!
----- Original Message -----
From: Bill Maxwell
To: rebel-builders@dcsol.com
Sent: Tuesday, October 16, 2007 4:49 PM
Subject: Re: [rebel-builders] vhf radio


'Fraid not Rick, cant make it. But wasn't Cowra the place to escape from?
----- Original Message -----
From: "Rick Harper" <rjwh@optusnet.com.au>
To: <rebel-builders@dcsol.com>
Sent: Tuesday, October 16, 2007 4:33 PM
Subject: Re: [rebel-builders] vhf radio

I hope you guys are coming to the SAAA "Escape to Cowra" Convention -
this coming weekend !

Rick "Biggus" Harper
541R .... flying AGAIN
----- Original Message -----
From: gleeso
To: rebel-builders@dcsol.com
Sent: Tuesday, October 16, 2007 4:28 PM
Subject: Re: [rebel-builders] vhf radio


Tassie is even a long way from Australia. (sorry Bill, couldn't let
that go by)
Rebel 804 down under.




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