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Comparing Two Very Close Together AM Signals & Why I Hear One Way More Often

SomeRadioGuy

SomeRadioGuy

The vaugeries and magic of AM radio waves travelin through the ether are what got me interested in this business and even though i know exactly how the magic works, it still fascinates me.

I'm in McGrath, Alaska a community in the west central interior, about 250 miles NW of Anchorage which is 2000 miles away from the two towers in the google street view screen shots below.

The left tower is 790 Watt KIHH Eureka, CA which is fairly regular/commonly heard here and often enough, somewhat to mildly listenable to, at times, outright pile driving in.

The right tower is KATA 1340 Arcata, CA just 4 miles NE across Arcata Bay with 1kw. I just heard it for the first time last night.

Why this all happens fascinates me and makes me wanna figure out why. That oddity probably has a very scientific reason..I'm guessing KIHH's tower is more efficient/taller than 1/4 wave, hence its 790W and that taller tower possibly helps with skywave.

Plus I'm betting the location makes a difference. They're BOTH within about 1/2 mile of the water, BUT KIHH is right on the water looking NW towards me.. so KIHH has very very little to impede its trip to me via the Pacific Ocean

KATA would have to go over several miles of land to reach the Pacific Ocean and get to me.

I find that mildly fascinating, but I'm an nerd.

 
If one is right on the water, the low angle next to zero degrees above the horizon probably double skips easier across the ocean. The other may have a low angle obstruction. Kind of like trying to skip a stone with a slight elevation in the way of the water. More complicated, and less likel to skip.

Here is another interesting comparison, which I think we discussed before. McGrath, AK has an area of about 48 square miles and a population of 301. Paris, France has less area, about 41 square miles and a population of about 2,100,000.
 
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Schroedingers Cat said:
If one is right on the water, the low angle next to zero degrees above the horizon probably double skips easier across the ocean. The other may have a low angle obstruction. Kind of like trying to skip a stone with a slight elevation in the way of the water. More complicated, and less likel to skip.

Here is another interesting comparison, which I think we discussed before. McGrath, AK has an area of about 48 square miles and a population of 301. Paris France has less area, about 41 square miles and a population of about 2,100,000.
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Theyre both about 1/2 mile from Arcata Bay.. one just has a clear shot to the pacific, another doesnt.

Our population prob. isnt even 301 anymore. Its thought were closer to 275/280
 
It is possible atmospheric skywave propagation characteristics in that 330 degree path may be different enough between 790 and 1340 to be noticeable to you. Or maybe not.

790 antenna radiates slightly less higher angle signal than 1400, but probably not enough of a difference to matter.

It is not unusual for an AM station to have a less efficient antenna system than predicted. This is not pointing fingers, but it happens, sometimes due to factors beyond reasonable control.

From the aerial view 790 appears to be more likely to have a reasonably good ground plane within 500 feet of the tower. That is because all of what 1400 needs must be done by humans, and much of what 790 needs exists in nature. I mean close-in, not the ground path beyond about 1,000 feet from the tower.

With respect to your reception in Alaska the idea is having an efficient AM antenna system, and launching a sky wave.

Software tells a story about predicted AM broadcast skywave propagation that might surprise you. It support the proposition that a well designed network of Class A stations can be a robust and durable method of independent communication at night, to the public or as back-haul to last mile local distribution via other methods.
 
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Greg Strickland said:
It is possible atmospheric skywave propagation characteristics in that 330 degree path may be different enough between 790 and 1340 to be noticeable to you. Or maybe not.

790 antenna radiates slightly less higher angle signal than 1340, but probably not enough of a difference to matter.

It is not unusual for an AM station to have a less efficient antenna system than predicted. This is not pointing fingers, but it happens, sometimes due to factors beyond reasonable control.

From the aerial view 790 appears to be more likely to have a reasonably good ground plane within 500 feet of the tower. That is because all of what 1340 needs must be done by humans, and much of what 790 needs exists in nature. I mean close-in, not the ground path beyond about 1,000 feet from the tower.

With respect to your reception in Alaska the idea is having an efficient AM antenna system, and launching a sky wave.
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KIHH is on 1400.



I think the water path for 1400 and its clear shot to the pacific helps
 
Typo, thanks for the correction.

btw- over the air broadcasting (especially AM) is to communication what the railroad is to transportation.
If both are one day gone, things become much more difficult for newer things.

To that point, in some urban areas a major problem with mass transit is obtaining right of way. And in many of these urban areas excellent rail lines were removed and the right of ways dissolved.

Los Angeles had the trolley line from downtown to Santa Monica (as I understand it) and right here in Annapolis a perfectly good rail right of way is transitioning to other uses, thereby multiplying cost of creating a local system.

As I understand it, one of Amtrak's biggest problems is right of way. It is not the cost of high speed rail and trains from DC to Boston, it is the near impossibility of obtaining right of way.

Back to the topic- at AM band frequencies someone could tell you how many reflection points in the ionosphere are likely in the path from Eureka CA to McGrath AK. And the typical range of departure angles from Eureka for that path.

The electrical charge of the ionosphere is fluid and ever changing at different altitudes and locations. Comfortably predictable, yet changing, like the weather.

There is a lot to it...

Past the math, there is some plain language in this one:


Not this one:

 
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Those oddball power levels are confusing. They ought to go back to nominal power levels. Face it, the 790 watt station is a 1000 watt nominal power station. Some stations are still running reduced input powers from many decades ago. If a nominal power 5000 watt station was squeezed in decades ago with reduced efficiency, it doesn't want to be called a 3800 watt station, and doesn't have to unless they move or otherwise relicense.

The Ocean and the Ionosphere act like a wave-guide with the multi hop propagation path, very little loss at at the small angles of reflection. Even the Great Lakes, which have recently been confirmed to have considerably higher conductivity than M-3, and can act like a waveguide with the Daytime skywave present during many hours, from lower layer heights, especially in the Winter. WTIQ 1490 Manistique seems to skip across Lake Michigan quite a bit in the Daytime, and the ground waves from inland stations are attenuated by lower than M-3 conductivity. You can detect that Daytime skywave is occurring with a field strength meter with considerable fading, even if the AGC masks it on most radios. I've noticed considerable Daytime fading from a 1000 watt Class IV/C station just 12 miles away.
 
Schroedingers Cat said:
Those oddball power levels are confusing. They ought to go back to nominal power levels. Face it, the 790 watt station is a 1000 watt nominal power station. Some stations are still running reduced input powers from many decades ago. If a nominal power 5000 watt station was squeezed in decades ago with reduced efficiency, it doesn't want to be called a 3800 watt station, and doesn't have to unless they move or otherwise relicense.

The Ocean and the Ionosphere act like a wave-guide with the multi hop propagation path, very little loss at at the small angles of reflection. Even the Great Lakes, which have recently been confirmed to have considerably higher conductivity than M-3, and can act like a waveguide with the Daytime skywave present during many hours, from lower layer heights, especially in the Winter. WTIQ 1490 Manistique seems to skip across Lake Michigan quite a bit in the Daytime, and the ground waves from inland stations are attenuated by lower than M-3 conductivity. You can detect that Daytime skywave is occurring with a field strength meter with considerable fading, even if the AGC masks it on most radios. I've noticed considerable Daytime fading from a 1000 watt Class IV/C station just 12 miles away.
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1400 is using a tower taller than 1/4 wave i found out, so more efficient than it needs to be, hence the lower power.

I used be on WTIQ 1490, and the other Maverick country stations overnight.. was there for several years
 
Sometimes, when they go to a taller tower, they have to reduce to not increase overlap with other stations. Some stations can go all the way up to 5/8 wavelength without reducing input power. Sometimes they make conductivity measurements to do so. Many stations used to use SLRs, Series Limiting Resistors, to run at the nominal power, 250, 500, 1000, 5000, 10000, and 50000 watts. Then they allowed reduced input at licensed nominal power so as not to waste energy. At one time, there was also 100 watts Daytime, and 2500 and 25000 were added later, and some special cases over the years.
 
Schroedingers Cat said:
Sometimes, when they go to a taller tower, they have to reduce to not increase overlap with other stations. Some stations can go all the way up to 5/8 wavelength without reducing input power. Sometimes they make conductivity measurements to do so. Many stations used to use SLRs, Series Limiting Resistors, to run at the nominal power, 250, 500, 1000, 5000, 10000, and 50000 watts. Then they allowed reduced input at licensed nominal power so as not to waste energy. At one time, there was also 100 watts Daytime, and 2500 and 25000 were added later, and some special cases over the years.
Click to expand...

The last remaining 100 watt full time AM only disappeared about 15 years ago, 1340 in Oil city, Pa
 
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