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AM RADIO PATTERNS

O

OldChicago

Just curious and to why the patterns non-directional stations in Chicago
(like WGN, WBBM, WNTD DAYS) are not completely circular? The have variations in the patterns at a 12 O'Clock, 3, and 8 O'Clock position? Could someone explain?


Old Chicago
 
These are drawn according to M-3 Conductivity Maps. Conductivity is better in some directions than others, so the signal goes further in different directions. M-3 is notoriously inaccurate in some areas, but according to a very respected consulting engineer I discussed this with, M-3 is quite accurate around the Chicago area. Some of the data used to generate the M-3 Map may have been from the stations you mentioned, even though they are nondirectional. The measured readings used to generate the 15 mmho/m patch that starts near the WLS tower and extends to St. Louis appears to be from measured WLS radials. Usually measured conductivity data is generated when directional antennas are proofed in the traditional way. You can find it in many recent applications on the internet. As the data are used to support the applications, some consulting engineers question the accuracy of the data. There are also seasonal variations due to temperature and moisture conditions of the soil. Radio Locator does not address those variations.
 
If you're referring to the maps you see on Radio-Locator, those aren't pattern maps. They're coverage estimates, which take into account both the station's own radiated pattern and the effect of ground conductivity on that signal's propagation. The ground conductivity around any given transmitter site is never uniform in all directions, and so a station that's radiating non-directionally will still get out better in some directions than in others. (Think of WLS, which shoots for hundreds of miles over the open farmland to the south but gets lost in the paved-over urban landscape 25 miles north in downtown Chicago!)

The Radio-Locator maps are actually estimates twice over - R-L's algorithm for calculating coverage is only an approximation to begin with, and it's based on FCC conductivity maps that are also very approximate. It also doesn't help that real-world conditions vary from day to day and from year to year; the ground conductivity of central Illinois was surely better a few years back, when the soil was nice and damp, than it is this dry, dusty August.
 
Here's a link to a small M-3 Map

http://www.fcc.gov/encyclopedia/m3-...d-states-wall-sized-map-am-broadcast-stations

There were problems in the past with the AM directional patterns on R-L. Those appear to be fixed. There now appears to be problems with FM DA patterns.

Non circular nondirectional FM patterns have to do with terrain height from 2 to 10 miles being different in different directions.

AM on R-L shows 2.5, 0.5, and 0.15 mV/m contours. FM shows 60, 50, and 40 dBu contours. One very prevalent misconception is that the inner contour is the city grade contour. It isn't. And this leads to many false claims of city grade service by persons who don't understand this. AM is 5 mV/m, FM is 3.16 mV/m or 70 dBu for city grade, which is well inside the inner contour on R-L.

Actual AM and FM directional patterns can be found on AM Query and FM Query. In the case of nondirectional patterns, they are theoretically circular.
 
The big map for the Chicago area is 30e in the directory that comes up when you click the link at the bottom. It's much more detailed and legible. But it still may have inaccuarcies based on the original data used, and the limitations of that data. When that map was made, there were relatively few directional antennas or powerful stations that made labor intensive groundwave studies.

An example of an area that I am familiar with that had few measured conductivity studies until recently is Northern Lower Michigan. Until the 1950s or so, there was not a single station that operated with more than 1 kW or with a directional antenna. Hence, no measured data was filed or needed to be filed for a typical Class IV station operating with 250 watts. An engineer might have taken a few out of curiosity, but they were maps just used internally or locally to demonstrate service areas to advertisers.

Another piece of information is that a WSCR engineer once told me that the conductivity in their antenna farm area (WSCR, WGN, WBBM, the then WAIT 820, and WMBI) was 20-30 mmhos/m.
 
Schroedingers Cat said:
The big map for the Chicago area is 30e in the directory that comes up when you click the link at the bottom. It's much more detailed and legible. But it still may have inaccuarcies based on the original data used, and the limitations of that data. When that map was made, there were relatively few directional antennas or powerful stations that made labor intensive groundwave studies.

An example of an area that I am familiar with that had few measured conductivity studies until recently is Northern Lower Michigan. Until the 1950s or so, there was not a single station that operated with more than 1 kW or with a directional antenna. Hence, no measured data was filed or needed to be filed for a typical Class IV station operating with 250 watts. An engineer might have taken a few out of curiosity, but they were maps just used internally or locally to demonstrate service areas to advertisers.

Another piece of information is that a WSCR engineer once told me that the conductivity in their antenna farm area (WSCR, WGN, WBBM, the then WAIT 820, and WMBI) was 20-30 mmhos/m.
Click to expand...
Is that 20-30 number high, low or average? I know I can hear 670 on Memorial Drive in St. Louis (outside the KMOX studios), almost all the way to the Twin Cities, and on the outskirts of Columbus, Ohio., while 720 sneaks onto the dial in southern Kentucky. That seems to be pretty good mid-day reach. (I can't imagine what WMT-600 would do with 50 KW.)
 
20-30 mmhos is very good ground conductivity indeed. Many parts of New England are lucky to get to 1.
 
boiseengineer said:
They call New Hanpshire "The Granite State" for a reason. Granite doesn't conduct RF.
Click to expand...

Neither does sand. Northwest Florida shows on the M3 as 1 mmhos/m, I've done proofs there that measured less than half of that.

Bob
 
Dr. Bob said:
boiseengineer said:
They call New Hanpshire "The Granite State" for a reason. Granite doesn't conduct RF.
Click to expand...

Neither does sand. Northwest Florida shows on the M3 as 1 mmhos/m, I've done proofs there that measured less than half of that.

Bob
Click to expand...
Would I be right in thinking that extends to south Georgia? WSB fades out quickly south of Macon (and maybe north of it; the memory fades too!).
 
As a business traveler and radio geek for 30+ years, I've been all over the U.S....as well as pretty good sized chunks of Canada and the UK. From my own experience....and borne out by the map....I would have to say that the absolute worst ground conductivity in the U.S. is in northern New England and the western portion of the Florida panhandle. The northern half of Florida and adjacent areas of Georgia also tend to be pretty bad....as is most of the southeast. Parts of the far west and upper Midwest are also pretty terrible.

"Sweet spots" with good conductivity include most (but not all) of the Midwest, southern parts of Texas and Louisiana, as well as the area around Salt Lake City (and points south). The prairie provinces of Canada also have great ground conductivity.

Finally, a note about 820 in Chicago. This signal, in its WAIT days, got out much better than it does now. Back then, the stick was by an old chicken farm just north of Elmhurst. Wide open spaces and really good ground conductivity (as explained in a previous post). Now...and going back to the days when it was the home for WSCR....820 is diplexed and situated in a more urbanized location with ground conductivity that's not quite as good.
 
Are there a lot of chicken farms out there? Perhaps the uric acid and rainwater has increased the ground conducitvity. One link I found said that uric acid ions are on the same order as sodium ions in determining conductivity of certain solutions. Perhaps adding free range chickens to your radial field could increase effective conductivity. Just make sure to have some good boots when walking out to the doghouses.
 
Schroedingers Cat said:
Are there a lot of chicken farms out there? Perhaps the uric acid and rainwater has increased the ground conducitvity. One link I found said that uric acid ions are on the same order as sodium ions in determining conductivity of certain solutions. Perhaps adding free range chickens to your radial field could increase effective conductivity. Just make sure to have some good boots when walking out to the doghouses.
Click to expand...

....LOL! I'm not sure if the old WAIT transmitter was in the chicken farm or next to it. Both the stick and the farm are gone now. Presumably as well as any stench or "residue"!
 
While on a recent trip to IL IA, MO, KS, NE I noticed that when one hit seek or scan in certain areas there were many strong stations. Go 5 or 10 mi and there were only a few. So there are some hot and cold spots not too far from one another. But for a New Englander, i was in reception heaven.
 
vibe said:
While on a recent trip to IL IA, MO, KS, NE I noticed that when one hit seek or scan in certain areas there were many strong stations. Go 5 or 10 mi and there were only a few. So there are some hot and cold spots not too far from one another. But for a New Englander, i was in reception heaven.
Click to expand...

You do run into some of this in the Midwest.....especially Minnesota, Wisconsin, and Michigan. Not so much in the states you mention.....with the notable exception of the Sand Hills of Nebraska. That's a sparsely populated area in parts of the western and northern area of the state with lousy conductivity.
 
Probably the best indicator of ground conductivity effects is Radio-Locator's coverage maps of the New York City stations. Many big AMs have their transmitters west of NYC, within eyesight of each other in Jersey. They all beam southeast to drill their signals into the City. WABC is about 6 miles north of the Meadowlands and WFAN/WCBS is east of the City and located near New Rochelle. WABC, WFAN and WCBS are non-directional 24/7.

Salt water has a conductivity of 5,000 mS/m. Long Island has a ground conductivity of 0.5 to 1 mS/m. The coverage map of any one of the big NYC AMs clearly demonstrate the amount of signal degradation caused by L.I's poor ground conductivity in stark comparison to excellent salt water conductivity.

-
 
Been over this issue before, but continue to be baffled why I find interference and difficulty tuning on radio the signal of WLS AM here in southern Lake County Illinois. My friend said it's being jammed by someone not fond of it's format. When I lived in Central Illinois in the 50's and 60's, it's signal boomed, and here I am in Chgo metro area and their signal behaves like a puny directional antennae. People have responded before, but it seems some engineering should be done.
 
howardm said:
Been over this issue before, but continue to be baffled why I find interference and difficulty tuning on radio the signal of WLS AM here in southern Lake County Illinois. My friend said it's being jammed by someone not fond of it's format. When I lived in Central Illinois in the 50's and 60's, it's signal boomed, and here I am in Chgo metro area and their signal behaves like a puny directional antennae. People have responded before, but it seems some engineering should be done.
Click to expand...

If you're in Lake Co., WLS's transmitter is considerably further away than those of WSCR, WBBM, WGN, or WMVP. I'm betting the ground conductivity over the path to Tinley Park is considerably worse than that over the path to Schaumburg as well.

In Central Illinois, you were closer to WLS -- and the conductivity to WLS was probably better than that to the other four.

Certainly WLS's signal in the Milwaukee area, where I grew up, is a LOT worse today than that of the other four stations cited. I don't remember it being that bad when I lived there. (which might suggest there's something wrong with the WLS antenna) On the other hand, I left in 1977 when there wasn't nearly as much RF noise in a typical home -- so WLS may have been weaker & we just never noticed.

(with the new 50kw facility south of town & the better conductivity and lower dial position, I'm betting Milwaukee's WTMJ is stronger in southern Lake Co. than WLS, at least during the day..)
 
w9wi said:
(with the new 50kw facility south of town & the better conductivity and lower dial position, I'm betting Milwaukee's WTMJ is stronger in southern Lake Co. than WLS, at least during the day..)
Click to expand...

I'm in southeast McHenry county....about 7 miles from the Lake County line. Daytime signals of WTMJ and WLS here are fairly similar per FMscan. WTMJ, is however, just a "tick" stronger with equiv of 6kw aimed at me. (60 dBuV versus 55).
 
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