Line Of Sight Question
 

Hello,

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Thanks,
Bob

Line Of Sight Question
 

"Robert11" wrote in news:SK-
:

Hello,

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Thanks,
Bob



Hi Bob

The propagation of radio signals is frequency dependent, not modulation
mode dependent. That is not to say that some modulation modes are not
better over long distances than others, SSB is better than AM and AM is
better than FM. To say that VHF frequencies are always line of sight is
also not completely correct. They are propagation modes that can extend
the range of VHF signals quite a bit. I have worked stations on 144MHz
that were more than 500 miles away. But these are not an everyday thing
so it safe to say that most of the time VHF is line of sight. 800MHz is
in the UHF band and is even more just line of sight than VHF but they are
still propagation modes that can extend the range out to 100’s of miles.
Line of sight propagation is the reason that VHF and UHF antennas are put
up high as it extends the line of sight.

John Passaneau W3JXP

Line Of Sight Question
 

"Robert11" wrote in message
...
Hello,

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Thanks,
Bob
It is not the type of transmission (AM, FM, SSB) but the frequencies that
determin the line of sight. For the most part any frequency much above 30
mhz will be line of sight most of the time.

In a few years when the sun spots come back, frequencies up to 50 mhz or
slightly more will become more useful for distances greater than line of
sight.

There will be times when you can receive transmissions at much greater
distances on almost all frequencies. I have worked stations over 500 miles
away many times on 144 and 432 mhz. This is not normal, but it can hapen.
This is with simple antennas and 25 watts of power. More power and better
antennas will give beter results.

Line Of Sight Question
 

On Fri, 11 Apr 2008 08:02:04 -0400, "Robert11"
wrote:

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Hi Bob,

John and Ralph pretty much cover some of the familiar turf. I would
add (or perhaps extend what has been said) that atmosphering ducting
can extend that range thousands of miles.

One example that I personally observed (quite literally) was watching
TV programining out of Edmonton and Calgary Canada while I was living
in Colorado Springs, Colorado. There were times I could watch an
entire movie before the duct faded away.

73's
Richard Clark, KB7QHC

Line Of Sight Question
 

Robert11 wrote:
Hello,

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Thanks,
Bob

Andy replies:

While I agree with the other posters, let me add that "line of
sight"
represents the best possible circumstances, and then only in free
space.

To test this, take your 2 meter handi talki and start up a
conversation
and then walk behind a car, or big truck. Nearly every time you will
be able
to maintain your conversation, even tho you are no longer in "line of
sight".

The environment is so full of reflections that it's like standing
in a hall
of mirrors with a flashlight. Many times you can drive thru a tunnel
without
losing the link. Other times you will lose a signal when you drive
by
light poles. (This is especially noticeable with your FM radio and a
weak signal).

While the radio waves travel propagate thru a non-homogenous
medium with
lots of things present that don't represent 377 ohms, each one of them
causes a reflection that will combine with the original vector, and
can
create sharp nulls or slight enhancement. Also, the combined signals
can effectively make the path of the signal "bend"....

So, while "line of sight" is the simplest answer, I have rarely
found
it to be correct. The close you get to "free space", the more
realistic
it is...... but that hardly ever happens when standing on earth...

Andy W4OAH

Line Of Sight Question
 

On Sun, 13 Apr 2008 11:18:06 -0700, Richard Clark
wrote:

On Fri, 11 Apr 2008 08:02:04 -0400, "Robert11"
wrote:

For the scanner frequencies around 118 MHz, e.g., I realize FM is
essentially line of sight.

Are AM transmissions also line of sight ?

Same question, but for the higher freq's around 800 MHz ?

Hi Bob,

John and Ralph pretty much cover some of the familiar turf. I would
add (or perhaps extend what has been said) that atmosphering ducting
can extend that range thousands of miles.

One example that I personally observed (quite literally) was watching
TV programining out of Edmonton and Calgary Canada while I was living
in Colorado Springs, Colorado. There were times I could watch an
entire movie before the duct faded away.

73's
Richard Clark, KB7QHC

Yup, ducting, meteor scatter etc can all provide extended VHF range.
I've only done about 250 miles on 2 meters, though on 6 meters my
farthest contact was about 3000 miles...........did as straight a line
as I could on MS Streets & Trips to 'calculate' that so there may well
be some error.

That was pretty good range for a video signal to carry, Richard; was
that on an older tv that actually allowed you to [fine] tune?

Line Of Sight Question
 

On Mon, 14 Apr 2008 20:26:09 -0700, wrote:

One example that I personally observed (quite literally) was watching
TV programining out of Edmonton and Calgary Canada while I was living
in Colorado Springs, Colorado. There were times I could watch an
entire movie before the duct faded away.

73's
Richard Clark, KB7QHC

Yup, ducting, meteor scatter etc can all provide extended VHF range.
I've only done about 250 miles on 2 meters, though on 6 meters my
farthest contact was about 3000 miles...........did as straight a line
as I could on MS Streets & Trips to 'calculate' that so there may well
be some error.

That was pretty good range for a video signal to carry, Richard; was
that on an older tv that actually allowed you to [fine] tune?

Yes, it was. And I was very much younger (a reverse convergence in
this somewhere). This was in the mid-1960s, summer time, antenna
pointed generally north, low band TV. The view north was a clear shot
to the horizon at a high point of roughly 6400 feet (average terrain
at least 6000 feet).

I also worked in a TV shop at the time (summers and weekends) and had
experience with 100s of "tuners" for TV. Some were works of art, some
trash, and few really helped because Colorado Springs was not a
metropolitan area and far from Denver. We did have one advantage
however. The local TV transmitters were atop Cheyenne Mountain. That
had about a 1 mile height advantage over the average terrain to the
east. It was also ground Zero for probably a good percentage of the
Soviet nuclear arsenal. I lived, perhaps, two miles from the front
doors (direct hit-proof blast doors, those) of NORAD.

73's
Richard Clark, KB7QHC

Line Of Sight Question
 

wrote in message
...
Yup, ducting, meteor scatter etc can all provide extended VHF range.
I've only done about 250 miles on 2 meters, though on 6 meters my
farthest contact was about 3000 miles...........did as straight a line
as I could on MS Streets & Trips to 'calculate' that so there may well
be some error.


Evidently line of sight means different things. I take it as the common
used formula of the square root of the height in feet is equal to the miles
to ground modified by about 1.2 to 1.4 for the way the radio waves bend
around the earth.

Good stations using ssb and a couple of hundred watts can work close to 250
miles almost any time on 2 meters and 432 MHz. I have worked over 800
miles (North Carolina to Texas and the end of Florida ) several times on 2
meters. Also close to that on 432.

Not sure how you want to calculate it, but have also worked England via a
satellite that was out to around 22,000 miles.

Line Of Sight Question
 

On Tue, 15 Apr 2008 18:18:26 -0500, "Ralph Mowery"
wrote:


wrote in message
.. .
Yup, ducting, meteor scatter etc can all provide extended VHF range.
I've only done about 250 miles on 2 meters, though on 6 meters my
farthest contact was about 3000 miles...........did as straight a line
as I could on MS Streets & Trips to 'calculate' that so there may well
be some error.


Evidently line of sight means different things. I take it as the common
used formula of the square root of the height in feet is equal to the miles
to ground modified by about 1.2 to 1.4 for the way the radio waves bend
around the earth.

Good stations using ssb and a couple of hundred watts can work close to 250
miles almost any time on 2 meters and 432 MHz. I have worked over 800
miles (North Carolina to Texas and the end of Florida ) several times on 2
meters. Also close to that on 432.

Not sure how you want to calculate it, but have also worked England via a
satellite that was out to around 22,000 miles.

I was not trying to imply my contacts were line of sight, guess I
didn't make that fully clear. Agree on the normal way to figure line
of sight - unless of course you are buying the "28 mile GMRS/FRS"
radios 8-}

Line Of Sight Question
 

wrote in message
...
I was not trying to imply my contacts were line of sight, guess I
didn't make that fully clear. Agree on the normal way to figure line
of sight - unless of course you are buying the "28 mile GMRS/FRS"
radios 8-}

I don't recall the type or service but those radios that run less than 1
watt and sell for about $ 29.95 a pair must be the ones you are talking
about. I know a couple of hams that have exceeded that distance by a whole
lot. One of the hams was on top of Mt. Mitchell (highest point on the east
coast).