R-L Maps

[Ai4i]

I listen to these two FMs while driving north, south, east, and west with buildings or trees on my right, left, ahead, and behind. I am in totally flat Southeast Florida. Can't really measure field strengths, but I always find that the areas at which these two stations are equal are at least ten miles different from what Radio-Locator shows.
WKCP and WXEL should overlap 60dbu in central Broward County, yet invariably they seem to do it in far north Broward, almost Palm Beach County. As the two stations are just five channels apart, my radio and antenna are ruled out as culprits.
Comments, thoughts?

 

[DanStrassberg]

R-L's disclaimer says that their maps are provided for entertainment purposes only. They neglect many important effects. For FM's in flat country like Florida, I don't know what those effects might be, but I am no expert. Years ago, a friend who was indeed an expert on FM coverage noted that, at that time, R-L's FM coverage maps neglected the effect of DAs. I think that problem has since been rectified but I'm not sure.

 

[rfry]

WXEL uses a directional radiation pattern, and the 1 mV/m contour calculated for it probably is closer to reality than for the same contour shown for omnidirectional WKCP.

Most "omni" FM transmit antennas are side-mounted on a tower, and their radiation patterns as installed typically are unknown The tower will affect/distort their free-space radiation patterns, especially the vertically polarized component (see paper 6 at http://rfry.org). This can cause unexpected variations in their coverage contours.

The Radio-Locator map for the 1 mV/m (red) contour of WXEL appears to be fairly close to, but not exactly the same as shown for WXEL on the FCC website (see http://i62.photobucket.com/albums/h85/rfry-100/WXEL_Compare.gif). However it also appears that the Radio-Locator calculations/maps are not based on an omnidirectional radiation pattern from WXEL.

Another item in the mix is the pattern of the receiving antenna in your vehicle. Most likely that is not omnidirectional, either, and it looks like the two stations are about in opposite directions from central Broward county.

Probably some combination of the above effects accounts for the differences you described.

 

[Ai4i]

Let me add the following extra details:
My antenna is a vertical whip and my results represent driving all around the area in every direction and, to quote a favorite line of mine from the play and movie Chicago, "and then some". I wonder how different my results would be with a turnstile, halo, or "S" shaped omnidirectional horizontal antenna on the car (window antennas are too directional for any kind of discussion).
I am in WKCP's main direction of interest (NNE), yet WXEL has changed their location, height, and power more times since originally signing on than I can remember and each time, with more first, second, and third adjacencies to protect. The sharpest thorn in their side toward my direction is probably WAFG which would never have come on the air were it not for all that earlier shuffling around.

BTW...that quote from Chicago was the response a witness gave when being sworn in to testify!

 

[w9wi]

I listen to these two FMs while driving north, south, east, and west with buildings or trees on my right, left, ahead, and behind. I am in totally flat Southeast Florida. Can't really measure field strengths, but I always find that the areas at which these two stations are equal are at least ten miles different from what Radio-Locator shows.
WKCP and WXEL should overlap 60dbu in central Broward County, yet invariably they seem to do it in far north Broward, almost Palm Beach County. As the two stations are just five channels apart, my radio and antenna are ruled out as culprits.
Comments, thoughts?

These maps are based on the FCC's propagation curves. While Radio-Locator doesn't say so, I'd be almost certain they come from F(50,50) curves -- those are the curves the FCC uses to predict service area, and the ones you'll see if you pull up coverage maps on the FCC's site.

The red circle, for example, is the 60dBu F(50,50) service contour.

What F(50,50) means is that at at least 50% of the locations within the red circle, WKCP will deliver at least 60dBu of signal at least 50% of the time. At the edge of the 60dBu contour -- along the red circle -- WKCP will deliver *less* than 60dBu at half of locations. At least in theory.

Furthermore, those curves don't take terrain (admittedly not much of an issue in Florida!) or buildings (far more of an issue!) into account.

 

[rfry]

Furthermore, those curves don't take terrain (admittedly not much of an issue in Florida!) or buildings (far more of an issue!) into account.

According to the cut & paste below from the Radio-Locator website - their coverage plots do take HAAT into consideration.

Here is a link to a R-L map plot for a Denver station licensed as omnidirectional, showing a fairly extreme example of this: http://www.radio-locator.com/cgi-bin/pat?call=KYGO&service=FM&status=L&hours=U.

The effects of obstructions/reflections/refractions from buildings and other structures along and near the propagation path are not accounted for in all of this, of course.

From R-L
These maps are drawn using engineering data from the FCC. The coverage pattern for each FM station is calculated using the effective radiated power (ERP) of the station and the antenna height above average terrain (HAAT). The HAAT is calculated in all directions based upon the average ground elevation between 1.5 and 10 miles from the station in each direction.

 

[joebtsflk1]

Mountain state engineering I've found is lots of fun. In short, the only thing that matters is the l-r maps, as in Longley-Rice