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AM reception

B

bobdavcav

Hi all,
I was talking with a friend the other day and she said that after 9/11/01, DX was absolutely amazing. She said she was picking up stations she never had before, or hasn't since. Does anyone else remember this, and have any idea why this might have happened? Her theory was that all the ash in the air mixed up the atmosphere enough to provide interesting DX, also causing her to suggest to me to DX last night with lots of smoke in the air. I did, but didn't really get anything too interesting.
 
I would doubtr that. It may have been just a naturally clear night as far as storms were concerned (if you remember the weather across the entire eastern part of the country that morning). There shouldn't have been many AM stations off the air because of the tragedy. (FMs and TVs on WTC were affected). I'm listening now and its pretty good conditions
 
bobdavcav said:
Hi all,
I was talking with a friend the other day and she said that after 9/11/01, DX was absolutely amazing. She said she was picking up stations she never had before, or hasn't since. Does anyone else remember this, and have any idea why this might have happened? Her theory was that all the ash in the air mixed up the atmosphere enough to provide interesting DX, also causing her to suggest to me to DX last night with lots of smoke in the air. I did, but didn't really get anything too interesting.
Click to expand...

I have never heard of local pollution (smoke, car emissions, etc.) causing changes in AM or FM DX.

AM reflects at much higher levels of the atmosphere. It would not have been affected.

FM is often reflected by inversion layers; it is possible that an inversion layer could be created by a large forest fire or huge refinery fire, but it would be limited in effect to the immediate area. The terrible occurrence of 9/11 was a combination of explosions and structural damage and not as great as even a small forest fire so I doubt it had any impact on propagation.

Good question, though.
 
My assumption would be, ignoring just plain good ionospheric conditions, is no airplanes leaving contrails. But I can't come up with a causal explanation.
 
DavidEduardo said:
I have never heard of local pollution (smoke, car emissions, etc.) causing changes in AM or FM DX.

FM is often reflected by inversion layers; it is possible that an inversion layer could be created by a large forest fire or huge refinery fire....
Click to expand...

I had never heard of that....until just this morning.

My daughter, who now lives in Santa Monica and teaches at USC, is on a weekend getaway with our son in law on the Central coast. She texted us some pictures of Avila Beach shrouded in fog. To paraphrase her... "It looks gloomy, but its actually a good thing. The inland fires created an inversion layer. a marine layer, which in turn sucked in moisture and fog. And in the process kept the smoke and pollutants away from ground level."
 
I have heard a Daytime Skywave effect that seemed to be due to thunder clouds. So this was not in the Winter, although thunderstorms do sometimes happen in Winter. But according to Stevie Nicks, "thunder only happens when it's raining". Had to throw that in. What I heard between crashes of lightning, were the 1430 and 1540 from the Toronto Islands, about 225 miles from my RL, in the early afternoon as
I recall. Normally, there is no significant ground wave from there. Normally, I don't get ground wave from Toronto above CFRB 1010, though I suspect I could hear CHUM where the DA lobe was strong enough. You do hear the 1610, but that is Daytime Skywave, on a de facto clear channel due to just TIS stations in the US on 1610. I figure the weather clouds act as ionic reflecting layers, favoring short distance skywave under certain conditions.
 
CTListener said:
How do contrails affect AM reception?
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I can find no documentation on low frequency reflection on fast moving airborne devices.

I suspect that the effect would be so short lived that it would not ever be noticeable.

Daytime in the regular coverage area of a station, medium wave AM propagates by groundwave. At night, skywave is reflected off of two very high layers... well above the height of airplanes.

"Kennelly and Oliver Heaviside, is a layer of ionised gas occurring between roughly 90 and 150 km (56 and 93 mi) above the ground — one of several layers in the Earth's ionosphere. It is also known as the E region. It reflects medium-frequency radio waves."

And AM skywave sets down quite a ways from the transmitter site, depending of course on the angle of radiation determined by the electrical height of the tower; a shorter height will have a sharper (and closer return) angle of radiation as it does not flatten the outbound signal.
 
Schroedingers Cat said:
I have heard a Daytime Skywave effect that seemed to be due to thunder clouds. So this was not in the Winter, although thunderstorms do sometimes happen in Winter. But according to Stevie Nicks, "thunder only happens when it's raining". Had to throw that in.
Click to expand...

From Omena, MI (20 miles NNW of Traverse City) in the summer back in the early 60's I'd get daytime enhanced conditions across Lake Michigan to places like Green Bay, Escanaba, and even Milwaukee. This would occur when there were storm fronts over most of the lake and surrounding shore areas.

Even got daytime reception of Ispeming and Duluth-Superior once. The only problem was the lightening induced static.

I always thought that the effect was like a lower atmosphere polarized layer, but that was the theory of a 13-year-old.
 
It's very hard for even powerful thunderstorms to penetrate too far into the stratosphere, and the same is true for smoke from wildfires. I googled around and it seems 70,000 feet or so is as far as it gets. Keep in mind AM DX comes from signals bouncing off layers of the atmosphere 50 miles or more high. The World Trade Center fires were really nowhere near what it takes to penetrate that high.

It's possible that randomly there was good reception those days, but I would guess that the effect was mainly psychological. People were in a pretty heightened emotional state and your friend might just have been trying more carefully to find stations, maybe without even realizing it.
 
Schroedingers Cat said:
Are you sure that they weren't watching TV and FM channels that were off the air in New York?
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That's a good question. With so many stations off the air, there would be great opportunity to hear FM DX, and possibly TV ( lower channel analog) as well. I wonder if Hepburn has archive maps for that time frame?

BTW, we had an antenna fire a couple of years ago, and had to go silent on almost all the SLC stations for a few hours one night (sensitive VNA sweep of the community antenna). Many people said it was very eerie to find the spectrum so vacant. I wouldn't wish something like that to happen again, but I'd love to know if there was a planned test, and set up to do some DX'ing. As such, we weren't allowed to publicize what was going on.
 
Schroedingers Cat said:
Are you sure that they weren't watching TV and FM channels that were off the air in New York?
Click to expand...

She's upstate, so I can't imagine that many stations in her area would be off the air, am or fm. I'll have ask her again which stations she got on those days, but she thinks KFI might have been in there. She also said the effects lasted about a week, well after airline travel resumed, another thing debunking that theory.
 
CTListener said:
And she received KFI San Francisco during the day on 9/11? Something doesn't make sense here. I think two reception tales have somehow become conflated with each other as this thread has gone on.
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San Francisco? Wow, the skip even effected a COL change! If the upstate reception of 640 kHz was by day, it's hard to imagine KFI's drowning out WNNZ.
 
Could have just been a good DX night. In 2001 the sunspots were on the increase -- they peaked after 2002-2003 -- and September is when Fall DX conditions begin to kick in on MW and SW. Although there is an old adage that low sunspots mean better MW DX, I've found that it clearly is not the case. Higher sunspots also improves MW DX. And, like I said, 2001 was a year where they were on the increase.

The ash and other atmospherics wouldn't have affected AM DX any.
 
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