AM Band propagation question
 

Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.

My guess is that it must be a switch in the height of the reflecting
layer somehow, but I can't construct a really consistent picture.

MW always reflects, but the attenuation varies at lower levels with
solar angle, sun killing off the reflected signal.

It's not ``grey line'' because that path is nowhere near the direction
involved.
--
Ron Hardin


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

"Ron Hardin" wrote
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.
_______________

Could be interference between skywaves reflecting off different layers,
and/or with different numbers of "hops."

Richard Fry wrote:

"Ron Hardin" wrote
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.
_______________

Could be interference between skywaves reflecting off different layers,
and/or with different numbers of "hops."

It might be a slow lowering of the reflective height as the sun comes up on
the ionosphere, leading to a gap between one hop vs two hop coverage, and
nothing to do with absorption, I guess.

My puzzlement came from not seeing how absorption could be doing it. Maybe
it isn't and it's just geometry.
--
Ron Hardin


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

Ron Hardin wrote:
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.

My guess is that it must be a switch in the height of the reflecting
layer somehow, but I can't construct a really consistent picture.

MW always reflects, but the attenuation varies at lower levels with
solar angle, sun killing off the reflected signal.

It's not ``grey line'' because that path is nowhere near the
direction
involved.

ONe thought is that the station goes to full power, allowing a bit
of extra reception even if propagation has declined?

I think I've noticed something like this myself, though on other
stations, but I haven't been up that late recently to have it
fresh in my mind.

Michael

"Richard Fry" wrote in message ...
"Ron Hardin" wrote
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.

Could be interference between skywaves reflecting off different layers,
and/or with different numbers of "hops."

I'd be inclined to think that it's the F1 layer reforming, since the sun's already up
east of Ohio, and before the E-layer reforms, considering how low the sun angle is
right now. I'd expect a lot of fading with your first suggestion, but not an
outright "fade away". I think you'll also find that AM radio rarely will skip more
than once before it becomes unusable.
--
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wrote:
ONe thought is that the station goes to full power, allowing a bit
of extra reception even if propagation has declined?

I think I've noticed something like this myself, though on other
stations, but I haven't been up that late recently to have it
fresh in my mind.

I've seen that happen with other stations. But WFAN is 50000U1 - that
is, they run the same power (and (non)-directional pattern) all the time.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

Ron Hardin wrote:
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.

My guess is that it must be a switch in the height of the reflecting
layer somehow, but I can't construct a really consistent picture.

There are several different reflective layers. The F1 and F2 layers
are the primary ones for shortwave, but on 660 KC the lower layers
may be coming into play as well. Since they are at different altitudes,
as they rise and fall you may find some times when you are getting a
strong F1 reflection, then a dead time, then a strong F2 reflection.

MW always reflects, but the attenuation varies at lower levels with
solar angle, sun killing off the reflected signal.

It's not ``grey line'' because that path is nowhere near the direction
involved.

What you need is a way of measuring propagation time throughout the
path....
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

Hey Doug! Many years, no hear!

GeorgeC
W2DB (ex- WB2DYB)
Awstin, TX(LIN TV, etc)


"Doug Smith W9WI" wrote in message
...
wrote:
ONe thought is that the station goes to full power, allowing a bit
of extra reception even if propagation has declined?

I think I've noticed something like this myself, though on other
stations, but I haven't been up that late recently to have it
fresh in my mind.

I've seen that happen with other stations. But WFAN is 50000U1 - that
is, they run the same power (and (non)-directional pattern) all the time.
--
Doug Smith W9WI
Pleasant View (Nashville), TN EM66
http://www.w9wi.com

How 'bout this...while you're in Ohio, stations to the east are changing
patterns, etc, and maybe it's just a drop in interference TO WFAN, not an in
crease in their level. Then again...maybe...

-GeorgeC
"Ron Hardin" wrote in message
...
Why, like clockwork, does WFAN 660 NYC, received 500 miles west in
Central Ohio, fade away at (nowadays) 6am and later come back
strong for another hour? They're strong again like a local at
almost 7am now, for instance.

Not just a random once-in-a-while thing, but regularly.

My guess is that it must be a switch in the height of the reflecting
layer somehow, but I can't construct a really consistent picture.

MW always reflects, but the attenuation varies at lower levels with
solar angle, sun killing off the reflected signal.

It's not ``grey line'' because that path is nowhere near the direction
involved.
--
Ron Hardin


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

The secondary service area of most Class I-A stations, such as WFAN, was
limited to the local noise floor, until some of these stations were broken down
by the clear channel decision in the 1960s (affected 13 of the Eastern U.S.
Class I-A stations, and none of the remaning U.S. Class I-A clears), and until
the "Rio" treaty (affected the remaining Class I-A clears, of whatever
country).

After the clear channel decision, the secondary service area of those affected
Class I-A clears was about 1,500 miles, or more.

After "Rio", is was about 1,000 miles.

Now, it is much less, sometimes no more than 700 miles at best, and perhaps
much, much less at worst.