AM DX Reception Question

[storrs19]

I live in the Louisville, KY metro area and have a question. I use a CCRadioPlus (the older one that has the TV VHF band) but it does have a great AM tuner and antenna. After sundown (9pm onward) I can tune in 890 WLS (Chicago), 750 WSB (Atlanta) and 870 from New Orleans fine with no drift or loss of signal yet I can barely receive 700 WLW from Cincinnati which is much closer than the other two. As far as I know all three are 50kw stations so why is 700 so much harder to receive yet it is only 110 miles away? The only frequency in use close to 700 WLW here is 680 which is a low power (1kw) channel. The odd thing is I can get 700 WLW fine from 7am to about 6pm or so then the signal starts to fade and I have to keep tuning and moving the radio. Odd that it comes in better in the day time. Thanks in advance for any help.

Chad

 

[gar hi]

The reason that happens is because you are at that unique distance where you still have a groundwave that then interacts with the nighttime skywave and it's multipathing causing the fading and scrambling you hear.

The other stations you mention are skywave only and you are at about the right distance where the skywave is strong and mostly consistent.

The thing you mention happening with WLW I always used to notice at night when I lived in New Jersey about 80 miles from New York. All the big stations like WFAN, WOR, WABC, WCBS would often sound messy at night and not as good as the day.

 

[BRNout]

I live in the Louisville, KY metro area and have a question. I use a CCRadioPlus (the older one that has the TV VHF band) but it does have a great AM tuner and antenna. After sundown (9pm onward) I can tune in 890 WLS (Chicago), 750 WSB (Atlanta) and 870 from New Orleans fine with no drift or loss of signal yet I can barely receive 700 WLW from Cincinnati which is much closer than the other two. As far as I know all three are 50kw stations so why is 700 so much harder to receive yet it is only 110 miles away? The only frequency in use close to 700 WLW here is 680 which is a low power (1kw) channel. The odd thing is I can get 700 WLW fine from 7am to about 6pm or so then the signal starts to fade and I have to keep tuning and moving the radio. Odd that it comes in better in the day time. Thanks in advance for any help.

Chad

Chad, you're getting what's known as 'skywave/groundwave cancellation' on WLW. Others here can explain this better than I, but I'll give it a shot:

Basically, what you hear on 700 during the day is from 'groundwave' which is the AM signal that follows the earth's surface. This is the local "daytime" signal that is usually very stable and which can be impacted by the nature of the soil and surrounding environment. For example, many threads here have to do with how certain seaside locations (like Cape Hatteras, NC) are awesome for picking up distant groundwave signals during the daytime.

Now, at night, the AM signal that doesn't follow the ground contour and is transmitted skyward is bounced back to earth via enegized/charged layers of the ionosphere. Examples of those signals would be the distant stations that you can receive at night from places like the East Coast or Texas.

In the case of WLW, Louisville is at just the right distance where you are still able to pick up the groundwave signal, but are also getting the skywave signal that bounces in from the upper atmosphere. The skywave takes a little longer to get to you than the groundwave does, so they tend to cancel out. As skywave is often unstable, the cancellation comes and goes - but still makes it difficult to listen to the station. Ironically, you're too close to Cincinnati to hear WLW well at night - but also too far from them.

Any AM station that has enough signal to make it to the ionosphere will have such a cancellation zone, some are closer to their transmitter than others (there are many reasons for this). But, in essence, the listenable zone of a strong AM signal at night can be thought of as a bit of a reverse donut. For WLW, you're in the donut.

 

[BRNout]

Sorry gar, we were typing at the same time - but my slow internet connection failed to recognize that you already addressed the subject.

 

[storrs19]

Thanks guys. I've loved to DX since the mid 1980's and never knew about skywave / groundwave and how that worked. I'm not sure of the model number of my CC Radio it does have the Twin Coil Ferrite antenna and does out perform other radios I have though. It has the now useless TV VHF band as it is about 10 years old. I take it on business trips and like to DX at night when I am in different cities as well. Of course these days most stations are playing the same syndicated shows but sometimes you get lucky and find local information or sports broadcasts as well.

 

[vibe]

A perfect example was my AM lisenbing experience Sun nite while staying near Ringwood NJ (about 45 mi NW of downtown NYC). the 50 kw blowtorches on 660-770-880-1010 were perfect. But 1050-1130 (to a lesser extent) and 1560 were noticeably weaker defintely a function of the ground-sky cancellation and enhanced by the hilly, rocky terrain of Northern NJ. 570,a 5kw station, was really weak but 1100 Cleveland was city grade with no fades as was 900 out of Hamilton On.
But I had my sweetie with me so the DX ing was kept to a minimum..

 

[MarioMania]

I was in Columbus, OH 8 years ago visting my Uncle...

I couldn't even get 1220 from Cleveland & that is a 50kw station..I was in a motel at the time

 

[ddsparxx]

WHKW 1220 in Cleveland is currently directional toward southeast and north, with a null toward Columbus. That may be why you couldn't get 1220 in Columbus.

 

[schmave]

WHKW 1220 in Cleveland is currently directional toward southeast and north, with a null toward Columbus. That may be why you couldn't get 1220 in Columbus.

Yeah, the former WKNR's night signal in Columbus always has been horrific. Forget hearing it during the day. The null was and is so severe that reception in Mansfield was almost impossible.

 

[cyberdad]

By international agreement for many years, 1220 was designated as a Mexican clear channel. Because of that, for a long time, WGAR was the only U.S. 1220 allowed to operate at night. I'm not sure if the designation is still technically in place for 1220...and certainly numerous stations on the channel are now operating at night. But the severe DA pattern is still intended to protect Mexico City at night.

 

[cd637299]

Re the 1220....how does that explain CHSC? Was in Toronto in 1999 or so, and Cleveland & St Catharines seemed to be duking it out all night.

That's a night permit I'll never understand.

cd

 

[tanner]

The same thing happens to WSB in Rome Ga, about 75 miles out of Atlanta

 

[trusty]

By international agreement for many years, 1220 was designated as a Mexican clear channel. Because of that, for a long time, WGAR was the only U.S. 1220 allowed to operate at night. I'm not sure if the designation is still technically in place for 1220...and certainly numerous stations on the channel are now operating at night. But the severe DA pattern is still intended to protect Mexico City at night.

This brings up an interesting question (that just about answers itself, but here goes...). It's 556 miles between Laredo, TX and Mexico City. Because of the agreement, are stations on 1220 protecting Mexico City or do they protect the whole country beginning at the border?

 

[cyberdad]

By international agreement for many years, 1220 was designated as a Mexican clear channel. Because of that, for a long time, WGAR was the only U.S. 1220 allowed to operate at night. I'm not sure if the designation is still technically in place for 1220...and certainly numerous stations on the channel are now operating at night. But the severe DA pattern is still intended to protect Mexico City at night.

This brings up an interesting question (that just about answers itself, but here goes...). It's 556 miles between Laredo, TX and Mexico City. Because of the agreement, are stations on 1220 protecting Mexico City or do they protect the whole country beginning at the border?

I stand to be corrected, but IIRC, a country that was a party to the North American agreement could locate the dominant (1-A) station anywhere it wanted to. As a practical matter for Mexico, this usually (but not always) turned out to be Mexico City. Or in the case of 1220/XEB technically nearby elsewhere in the Mexican Federal District. Whether or not any portion of the agreement still applies to the former 1-A clears, I think it's probably safe to say that US stations on 1220 at night are protecting Mexico City (as opposed to the entire country) either by using a DA or operating with sharply reduced nighttime power (if not both).

If David's following this thread, he may know exactly where this stands today and perhaps he can update/clarify.

As for CHSC, I always thought this was a weird allocation myself, but the WHKW's null to the northeast is almost as severe as the one to Mexico.

"Back in the day" when all the U.S. 1220s had to be off at night, Cleveland (as WGAR) was a do-able...but still fairly tough...catch here in the Chicago area. The Canadians sometimes came through, but usually what you got was Mexico....although for some reason, usually not quite as strong as some of the other Mexicans.

 

[MarioMania]

WHKW 1220 in Cleveland is currently directional toward southeast and north, with a null toward Columbus. That may be why you couldn't get 1220 in Columbus.

Wait, I thought the antanna built Straight up..I'm I missing something "directional toward southeast and north" what does that mean??

 

[cd637299]

WHKW 1220 in Cleveland is currently directional toward southeast and north, with a null toward Columbus. That may be why you couldn't get 1220 in Columbus.

Wait, I thought the antanna built Straight up..I'm I missing something "directional toward southeast and north" what does that mean??

It means that the station sends its signal in those directions. Many stations have to direct their signal away from certain locations, to avoid interference.

cd

 

[gar hi]

WHKW 1220 in Cleveland is currently directional toward southeast and north, with a null toward Columbus. That may be why you couldn't get 1220 in Columbus.

Wait, I thought the antanna built Straight up..I'm I missing something "directional toward southeast and north" what does that mean??

Directional stations have more than one tower.

Having two ot more towers for one station allows them to choose a direction.

 

[ddsparxx]

When I said "directional toward southeast and north," I was looking at Radio Locator's coverage map of WHKW to indicate the directions the station was pointing to, if the reception was in daytime. The station uses 5 towers, according to what I saw on Google map of the transmitter location 41° 18' 26" N, 81° 41' 21" W from the Radio-Locator website.

 

[trusty]

Wait, I thought the antanna built Straight up..I'm I missing something "directional toward southeast and north" what does that mean??

To be more specific, it's not the antenna that's pointed in a direction; it's the signal. I believe when you see more than one tower at a station's transmitter, one antenna carries the signal; the other(s) amplifies or nulls the signal to make it spread out in a certain "directipn".