Radio Locator Coverage Maps

[eyg2181]

Why Is it that most of the stations map on radio locator are not drawn as big as they are... for example....the map of 93.3 WMMR in philadelphia shows that it cannot be heard in pottsville pa of ANY part of schulkill county at that, however.....i wouldnt even call the station fringe...as there is not much static at all...i would just call it distant...however the map shows it has no signal what so ever, when the signal is actually good for the distance it is...all you need is a piece of speaker wire to pull it in.

and some the maps are accurate...like Q104 in NYC that map is exactly right...it says Fringe in Levittown, and thats what it is...very weak.....u all know what i mean

 

[Tig1150]

These maps are based on the average terrain 0 to 10 miles out from the xmtr. Real world coverage is based on the actual terrain. To get true coverage (and it is never a circle) you need a computer model. The more flat land is the closer the average terrain maps will match the real world.

The FCC still uses the average terrain for protection and coverage so what you see on these maps is the legal coverage. Stations are protected to 60 dBu for class A and C FM's and 54 dBu for class B FM's.

If you are line of site to an FM xmtr and no other stations interfere you can hear an FM, no matter what the coverage map says.

 

[Grrrradio]

To expand on what Tig said, the contours match Radio-Locator's estimated calculation of specific numerical signal strengths. The blue line is 40 dBu, also known as 100 microvolts per meter, which is actually a fair amount of signal strength for those with sufficiently sensitive radios. So there may be plenty of signal coverage in points beyond that line... even if the map IS accurate for the station you're talking about. As Tig suggested, it's just that there are many other factors in play, such as terrain and what kind of radio you're using.

One example I have out here in the Twin Cities is KMOJ, a black community station on 89.9 in North Minneapolis. They run 1000 watts at what the FCC has calculated to be 79 feet above average terrain. I got really bored one day and calculated their line-of-sight distance to my parents' place in the boonies, then used FCC Curves to calculate the station's estimated signal strength. I got something like 37.7 dBu, and the Radio-Locator map confirmed it (we were a couple miles outside the blue)... but my car radio gave me very clear reception indeed. (God bless Delco! ;D)

Really, it's all about terrain, and there are plenty of points in southern Scott County that can "see" Minneapolis quite nicely. When I subsequently moved to St. Paul, I got quite the shocker while traveling 35E -- it goes through a valley north of downtown, and KMOJ is almost completely wiped out even though this location is halfway between its purple and red Radio-Locator contours!! (Even a 10-watt translator atop the IDS tower in Minneapolis -- with similar theoretical signal strength at this location, and a several-hundred-foot height advantage over KMOJ -- statics unbelievably at this location!)

 

[jd]

To expand on what Tig said, the contours match Radio-Locator's estimated calculation of specific numerical signal strengths. The blue line is 40 dBu, also known as 100 microvolts per meter, which is actually a fair amount of signal strength for those with sufficiently sensitive radios. So there may be plenty of signal coverage in points beyond that line... even if the map IS accurate for the station you're talking about. As Tig suggested, it's just that there are many other factors in play, such as terrain and what kind of radio you're using.

You're right; there are many factors and those maps are only an estimate, or as they say "predicted coverage." I checked the distance between the WMMR antenna and Pottsville, and it's about 75 miles. That's well outside the "service area" (60dBu) of the station, and far enough for the curvature of the earth to come into play. But instead of the WMMR signal "overshooting" Pottsville, the elevation there (about 680 feet) could make fairly good reception possible. That's providing, of course, that the signal has a relatively clear path to the particular location.

 

[PaulBWalkerJr]

Mr. Grrrradio..

You're always full of it.. information that is!! ;D

 

[davideduardo]

Why Is it that most of the stations map on radio locator are not drawn as big as they are... for example....the map of 93.3 WMMR in philadelphia shows that it cannot be heard in pottsville pa of ANY part of schulkill county at that, however.....i wouldnt even call the station fringe...as there is not much static at all...i would just call it distant...however the map shows it has no signal what so ever, when the signal is actually good for the distance it is...all you need is a piece of speaker wire to pull it in.

and some the maps are accurate...like Q104 in NYC that map is exactly right...it says Fringe in Levittown, and thats what it is...very weak.....u all know what i mean

Actually, from a broadcaster's perspective, the maps are highly misleading. In reality, something just inside the red, innermost contour is the "useful" coverage. Many studies have been done of where listening takes place. On FM, it is 85% inside the 70 dbu contour, with almost all the rest inside the 64 dbu.

While signals can be heard outside this contour, the stations on average do not get much listening beyond those areas in rated markets. Obviously, in sparsely populated areas with fewer stations, people will listen to more distant, and thus, weaker signals due to lack of alternative better signals.

On AM, it is even more extreme. In LA, for example, almost all listening is within the the 10 mv/m countours of the local AMs. This is because the noise levels on the AM band in big cities are so high that any lesser signal is plagued by man-made RF interference. Also interestingly, in adjoining, and less noisy, areas, listeners will tune to a weaker signal because it has less interference.

Keep in mind that the raidolocator maps are clearly market as being for amusiment purposes only. Many signals can be heard at great distances, but they don't get listening outside the primary signal areas.

 

[Grrrradio]

Actually, from a broadcaster's perspective, the maps are highly misleading. In reality, something just inside the red, innermost contour is the "useful" coverage. Many studies have been done of where listening takes place. On FM, it is 85% inside the 70 dbu contour, with almost all the rest inside the 64 dbu.

Just out of curiosity, how broad were these studies? Did they cover certain particular markets, or the nation at large? My curiosity stems in part from certain numbers I've seen in the Minneapolis Arbitrons, and it seems plausible that a study like the above could have different results in a market like ours than in a New York or Chicago (with many, many more tall buildings that could lead to multipath and other urban reception annoyances cutting down on the usefulness of sub-70dBu signals.) There are four signals in the Twin Cities which would seem to be enigmas in comparison with the study in question.

1) KBGY -- a Spanish station which transmits with 48 kW at something like 190 *feet*, 52 miles south of downtown Minneapolis and a similar distance from downtown St. Paul. It still manages to pull half a share in the Twin Cities book. Granted, there's a fairly sizable Hispanic population in its COL of Faribault, but I doubt the diary distribution is very strong near the Rice County transmitter site (which is well past even the furthest of far suburbs). The next-closest large Hispanic community lies in Shakopee, which does regularly get Twin Cities diaries, but it's still at something like the 55 dBu contour. By the time you finally reach the market's most significant Hispanic population, in Minneapolis Midtown, the signal is in the high 40s at best... yet the station regularly carries ads for businesses located in Minneapolis and St. Paul proper! Half a share is something like 10,000 cume in a market our size, which really isn't bad at all for an ethnically targeted signal that's fringe before it even hits the second-ring suburbs. (And this is in a city with THREE other Spanish formats, two of which regularly appear in the book!!)

2) WWJO, a St. Cloud country station that also regularly appears in the Minneapolis book with close to half a share. (St. Cloud is a college town of about 60,000, 70 miles northwest of the Twin Cities, yet has eight or nine stations all its own.) Yet this station's 60 dBu just barely nicks the Minneapolis exurb of Elk River (and as far as I know, the diary distribution area doesn't go much past this.) Several radio professionals in the Twin Cities market, who post on other message boards, claim the station is a significant factor even further down the line in Maple Grove, where its strength is somewhere in the mid-50s. Take their 10 share in St. Cloud (which is equivalent to about 16,000 cume in this smaller market), vs. an 0.4 in Minneapolis (8,000), and WWJO is getting fully a third of its listeners from outside its 60 dBu contour!

3) WFMP, back when it was classic-country WIXK and still licensed to New Richmond, Wisconsin. If memory serves, a good 80% of the metro population was outside its 70 dBu, and it frequently *exceeded* a 1-share. I'm guessing at least a decent chunk of this segment had to come from areas outside the 70.

4) The one that really confuses me -- KTTB-Glencoe. Urban format, transmitter 50 miles west of downtown, full class-C power but only on a 578-foot stick. By "quick and dirty" visual estimation from the R-L map, 60% of the geographical metro area and 50% of the metro population lie outside its 64 dBu... and it still pulls mid-3's, and over 4 in the last book, 12+... against a heritage CHR with a full 100 kW on the main metro antenna farm! Again, this is anecdotal, but many of my sister's friends went to Lakeville High School, which is right on the 60, and it was the most popular station there... also my pizza-delivery boss in Shoreview manages to pull it in at the store, which is definitely outside the 60 and well inside the 115 dBu blanketing contour of the multiple FMs on the antenna farm 3 miles away! Every inch of Minneapolis itself lies outside the 70 (it's about a 64 downtown.)

These, of course, could just be exceptions that prove the rule, which is why I was wondering about the specific places where these studies were conducted (and also the formats in question.) Perhaps the above signals do decently despite their fringe status only because Spanish and classic country are niche formats, or in the case of WWJO because regular country K102 has little competition in the Cities proper, or in the case of KTTB because there really is no other Urban format to speak of. It would certainly be interesting to find out more about these studies for purposes of comparison and discussion.

 

[davideduardo]

Just out of curiosity, how broad were these studies?

I know of many different broadcasters that have looked at the source of most listening, based on diary returns and quarter hours vs. the coverage maps. I have done this in over a dozen markets. Obviously, unique formats will get fringe listening and so will rural areas.


1) KBGY -- a Spanish station which transmits with 48 kW at something like 190 *feet*, 52 miles south of downtown Minneapolis and a similar distance from downtown St. Paul.

Probably the uniqueness, but it is also the long listening time of Hispanics, which converts low cume into higher than average shares.

2) WWJO, a St. Cloud country station that also regularly appears in the Minneapolis book with close to half a share.

The metro includes most of Sherburne County (this is a 13 county market, in fact) so probably most of the listening is in the area to the NW.


3) WFMP, back when it was classic-country WIXK and still licensed to New Richmond, Wisconsin.

The metro includes two counties in WI, and several East of the downtown area. I suspect they get most listening there.

4) The one that really confuses me -- KTTB-Glencoe. Urban format, transmitter 50 miles west of downtown, full class-C power but only on a 578-foot stick.

Wright and Carver counties are in the metro. Again, most listening is in the 70 on most stations, with a bit in the 64, and nearly nothing below. This format might force listeners to tolerate less favorable signals.

These, of course, could just be exceptions that prove the rule, which is why I was wondering about the specific places where these studies were conducted (and also the formats in question.) Perhaps the above signals do decently despite their fringe status only because Spanish and classic country are niche formats, or in the case of WWJO because regular country K102 has little competition in the Cities proper, or in the case of KTTB because there really is no other Urban format to speak of. It would certainly be interesting to find out more about these studies for purposes of comparison and discussion.

All excellent points. Remember, markets are made of many counties (there is a detailed list at arbitron.com) so you have to take into account that a lot of listening may be in the areas where the signal is better, and very little where it is not.

 

[Grrrradio]

Thanks for the info... was never aware that the metro books cover over a dozen counties. Having been mostly an outside observer to this business, I was under the assumption that most of the Arb diaries went to the seven-county area that the Met Council had long used as its definition of "metro"... or MAYBE the recent expansion to nine. Shows what I get for making unfounded assumptions!

 

[davideduardo]

Thanks for the info... was never aware that the metro books cover over a dozen counties. Having been mostly an outside observer to this business, I was under the assumption that most of the Arb diaries went to the seven-county area that the Met Council had long used as its definition of "metro"... or MAYBE the recent expansion to nine. Shows what I get for making unfounded assumptions!

This is a common problem when analyzing ratings... many markets are immense, with lots of counties.

Go to http://www.arbitron.com/radio_stations/mktdefs.asp and look at any US market...

One of the other issues is that many stations in the core of the market do not have enough signal to cover the whole market. A good example is San Francisco, where the market runs from santa Rosa to the North to Campbell to the south and only 3 or 4 stations, all AM, fully cover it day and night.

 

[pianoplayer88key]

Why Is it that most of the stations map on radio locator are not drawn as big as they are... for example....the map of 93.3 WMMR in philadelphia shows that it cannot be heard in pottsville pa of ANY part of schulkill county at that, however.....i wouldnt even call the station fringe...as there is not much static at all...i would just call it distant...however the map shows it has no signal what so ever, when the signal is actually good for the distance it is...all you need is a piece of speaker wire to pull it in.

and some the maps are accurate...like Q104 in NYC that map is exactly right...it says Fringe in Levittown, and thats what it is...very weak.....u all know what i mean

Actually, from a broadcaster's perspective, the maps are highly misleading. In reality, something just inside the red, innermost contour is the "useful" coverage. Many studies have been done of where listening takes place. On FM, it is 85% inside the 70 dbu contour, with almost all the rest inside the 64 dbu.

While signals can be heard outside this contour, the stations on average do not get much listening beyond those areas in rated markets. Obviously, in sparsely populated areas with fewer stations, people will listen to more distant, and thus, weaker signals due to lack of alternative better signals.

On AM, it is even more extreme. In LA, for example, almost all listening is within the the 10 mv/m countours of the local AMs. This is because the noise levels on the AM band in big cities are so high that any lesser signal is plagued by man-made RF interference. Also interestingly, in adjoining, and less noisy, areas, listeners will tune to a weaker signal because it has less interference.

Keep in mind that the raidolocator maps are clearly market as being for amusiment purposes only. Many signals can be heard at great distances, but they don't get listening outside the primary signal areas.

So, David, what would that 10mV/m signal usually sound like? Is that sufficient to have completely static-free (ok, we'll say 96dB signal-noise ratio for example) reception inside a metal building with computers and fluorescent lights all over the place (assuming that 10mV/m is measured outside the building)? Or, what would be a more likely scenario? (& what signal would be needed for the difficult-case scenario description I gave?) Also, approximately what strength signal would be needed for fairly clear reception (~54dB SNR) with a SuperRadio and a large loop antenna in a rural area, like, for example, western Arizona, northeastern Nevada, western Texas, eastern Montana, etc?

And is there some way I can find out the approximate mV/m signal strengths of various AM stations at my location (about 2 miles east of La Mesa and south of El Cajon in CA)? For example, using the built-in antenna on a walkman-style radio I use, at noon: 600, 690, 760, 910, 1130, 1170, and 1360 are pretty much crystal-clear; 540, 800, 860, 1210, 1240, 1470, and 1700 are fairly good with a little bit of static if the audio is otherwise quiet; 640, 740, 950, 1070, 1090, 1270, 1310 (actually, I don't listen to the upper-dial spanish ones much so since I've forgotten their relative strengths I won't list any more of them) have some noticeable static, but are still quite intelligible, and when combined with a Select-A-Tenna, are back in the clear. 570, 710, 790, 830, 1450, and a few others, are weak, but to my ear still quite listenable. 670, 930, 970, 980, 1050, 1110 (if 1130 is off the air, otherwise it's wiped out completely without an external loop antenna), 1280 and some others are very faint, but can still be identified with some difficulty. 530 (the TIS from LAX), 560 (until KLAC started IBOC), 590 (until KOGO started IBOC), 660, 730 (from Ensenada), 790 (Mexicali, can be heard under KABC), 820 (Mexicali), 850 (Mexicali), 1020, 1150 (difficult to tell if it's LA or Mexicali - could be either one - I think I've heard both but it's extremely faint), 1190, 1250, 1290 (Santa Barbara usually dominates in the daytime, but San Bernardino can also be heard when conditions are right, and is usually dominant of the two at night (except for the mex that wipes both out a lot of the time)), 1300 (Brawley), 1320 (Oceanside), 1330 (LA), 1340 (Santa Barbara), 1350 (San Bernardino), 1510 (Ontario), 1520 (Port Hueneme), 1530 (KFBK, sometimes, when conditions are right), 1540 (LA), 1560 (KNZR, when conditions are right), 1580 (KBLA, although KMIK sometimes competes and occasionally dominates when conditions are right), and a few others require a Select-A-Tenna to be heard at all, although on a few of those stations a faint hint that something's there can be detected with only the internal ferrite bar.

 

[vibe]

The maps are conservative IF one has a better than average car/home setup. That's just my opinion having driven in 26 states in the last 7 months.
My FM car radio is average and the maps are pretty accurate. The AM portion is very sensitive and get listenable stations well beyond the fring area contours in virtually all areas.

 

[davideduardo]

So, David, what would that 10mV/m signal usually sound like?
And is there some way I can find out the approximate mV/m signal strengths of various AM stations at my location

http://www.v-soft.com/ZipSignal/default.htm allows you to type in the zip code and it will tell you the signal strengths for local and fringe stations.

10 mv/m is not enough in some places, but is generally enough on AM to cover a nosiy metro well. An example would be one street in LA where KFI has over a 25 mv/m signal, but for years power line noise makes it unlistenable.