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#1
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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 |
#2
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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 |
#3
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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 |
#4
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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 |
#5
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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 |
#6
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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 |
#7
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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. |
#8
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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. |
#9
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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. |
#10
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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. |