Line Of Sight Propagation For AM signals ?
 

Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

Thanks,
Bob

Line Of Sight Propagation For AM signals ?
 

Robert11 wrote:

Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

What do you think?

dxAce
Michigan
USA

Line Of Sight Propagation For AM signals ?
 

Robert11 wrote:

But, is this also true for AM signals in this frequency range ?

Yes, the pure propagation is similar.

Regards,

Ralf

Line Of Sight Propagation For AM signals ?
 

On Sat, 13 Jan 2007 08:14:05 -0500, "Robert11"
wrote:

Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

This is generally true during hours of daylight. Medium wave signals
bounce off the ionosphere after dark thus allowing for long distance
reception.

--
Posted via a free Usenet account from http://www.teranews.com

Line Of Sight Propagation For AM signals ?
 

Tester wrote:

On Sat, 13 Jan 2007 08:14:05 -0500, "Robert11"
wrote:

Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

This is generally true during hours of daylight.

Huh?

Medium wave signals
bounce off the ionosphere after dark thus allowing for long distance
reception.

What the hell does medium wave have to do with the original question?

dxAce
Michigan
USA

Line Of Sight Propagation For AM signals ?
 

Robert11 wrote:
I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

Yes. (there is some limited refraction)

But, is this also true for AM signals in this frequency range ?

Yes.

It's the frequency of the signal that determines what path that signal
will follow to get from Point A to Point B. Signals on nearby
frequencies will follow the same path.

So, a "dead air" signal - a pure, unmodulated signal carrying no
intelligence - transmitted on 150MHz will cover a given path. If you
adjust the transmitter to 149.9MHz, the signal will cover the same path;
likewise if you adjust it to 150.2MHz.

Now, if you put some information on this signal... if you use FM, the
information - the voice, or data, or whatever - causes the frequency of
the signal to vary between limits. Say, between 149.95 and 150.05MHz.
The signal will cover the same path as it did when it wasn't carrying
any information at all.

If you use AM instead... the signal will still spread out near 150MHz.
It'll spread out over a narrower range, maybe between 149.995 and
150.005MHz. Still, since the frequency at any given moment is still
pretty close to 150MHz, the signal will follow the same path.

--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Line Of Sight Propagation For AM signals ?
 

On Sat, 13 Jan 2007 08:14:05 -0500, "Robert11"
wrote:

Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

Thanks,
Bob

Actually the MUF (maxiumum usable frequency) is the highest frequency
that propogates beyond line of sight, and the MUF is rarely beyond
about 30Mhz. On very rare occaisons it can get as high as about
60Mhz, but I don't think there is any record of it ever getting beyond
60 Mhz.

In general anything above 30Mhz is line of sight, regardless of the
modulation scheme (and mathematically, narrow band FM and AM are the
same creature). The Modulation scheme has nothing to do with how well
the signal bounces off the ionosphere.

Line Of Sight Propagation For AM signals ?
 

Robert11 wrote:
Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

Thanks,
Bob

No, AM signals above 150 mhz go straight down into the gound and cause
earth tremors, unless you're on the ocean, in which case they just
slosh around. SSB signals propogate outward from the antenna in a
spiral pattern. Digitally-encrypted FM signals above 150 mhz propogate
in a checkerboard pattern.

Sorry, couldn't resist. As far as I know, radio signals at a given
frequency will have identical propogation characteristics regardless of
transmission mode.

Line Of Sight Propagation For AM signals ?
 

Tester wrote:
This is generally true during hours of daylight. Medium wave signals
bounce off the ionosphere after dark thus allowing for long distance
reception.

Medium wave bounces off the ionosphere all the time; but attenuation
in the lower ionosphere keeps it from reaching it, in the daytime.

Higher frequency makes it through, but can be too high to bounce off
the ionosphere except in the daytime.

Hence the MW good at night (no attenuation) and SW good in the daytime
(enhanced ionosphere reflectivity).

A solar Xray flare can enhance attenuation even for SW to the point that
that band dies as well, but is unusual.
--
Ron Hardin


On the internet, nobody knows you're a jerk.

Line Of Sight Propagation For AM signals ?
 

Its the frequency, not the method of modulation, that affects how radio
waves are propagated. So yes, in the same 150 MHz frequency range, both
AM and FM signals are pretty much line of site.

In article ,
"Robert11" wrote:

Hello:

I understand that fm signals in the 150 MHz and higher range propagate
pretty much as line of sight.

But, is this also true for AM signals in this frequency range ?

Thanks,
Bob

--
Please reply to the group, not by email. The email address in the
header is not valid unless you remove the obvious.

Line Of Sight Propagation For AM signals ?
 

matt weber wrote:

Actually the MUF (maxiumum usable frequency) is the highest frequency
that propogates beyond line of sight, and the MUF is rarely beyond
about 30Mhz. On very rare occaisons it can get as high as about
60Mhz, but I don't think there is any record of it ever getting beyond
60 Mhz.

At the peak of the sunspot cycle the MUF is often above 30-Mhz in the
daytime for weeks or months. It's not that rare to reach 40-mhz when the
solar flux is close to 300.