Re: WLW and "Morning Edition"

[Dan.Strassberg@att.net]

If everything had been equal, increasing the power by a factor of 10 would have 
increased the signal strength everywhere by sqrt(10) or 3.16 times. However, 
except over salt water (and even that exception is only approximate), a tenfold 
power increase does not increase by anything close to 3.16 times the distance 
from the antenna to any specified contour (for example to the 0.5 mV/m contour, 
which represents the limit of the daytime primary service).

For an example, go to the FCC's CDBS database and open up the application 
(actually now a CP) of WXYT Detroit to increase from 5 kW-U DA-N to 50 kW-U DA-
2. Despite the tenfold power increase, the land AREA encompassed by the 0.5 
mV/m groundwave contour does not appear to even double. If the patterns were 
circular (and, of course, only the old 5 kW ND day pattern is even close to 
circular), you would have expected the radius of any given contour to increase 
by 3.16 times--that is by sqrt(10). Were that the case, the area enclosed by 
the contour would increase by 10 times. (The area within a circle is 
proportional to the SQUARE of the radius.)

It's a little complicated to explain why is the area increase so much smaller 
than you might predict. The most pronounced effect is that of the finite soil 
conductivity. Although the effect depends on the actual conductivity and the 
frequency, a fair first approximation is that the field strength at any given 
distance from the antenna is proportional to the square root of the antenna-
input power (times a multiplier for the antenna efficiency, which depends on 
the tower's electrical height) divided by the SQUARE of the distance from the 
antenna. Note that the divisor is NOT just the distance. Only over salt water 
does dividing by just the distance provide a fair approximation of the decrease 
in signal strength with increasing distance. The higher the frequency and the 
worse the soil conductivity, the greater the exponent to which you must raise 
the distance term in the divisor.

So for WLW, the 500-kW operation might have extended the coverage radius not by 
sqrt(10) but by something closer to sqrt(3). But there's more. WLW had to 
directionalize to protect CBL, which at the time was on 690. If you think about 
the effect, you will realize that directional operation costs a station some 
coverage area. It would not do so were it not for the effect of finite soil 
conductivity, but since infinite conductivity does not exist anywhere on earth 
(even over salt water), a DA ALWAYS costs an AM station some coverage area and 
the more directional the pattern, the greater the cost.

Anyhow, if you can follow it, there's your explanation. The allegation that the 
10-times power increase did not increase the groundwave coverage area is wrong, 
but it is closer to correct than you might think.
--
dan.strassberg@att.net
617-558-4205
eFax 707-215-6367
> On this morning's "Morning Edition," Bob Edwards had a 
> neat piece on the history of WLW Cincinnati and an album 
> put out by a pair of fellas (names escape me at the 
> moment) who also host an old-time radio show on an NPR 
> affiliate in Cincinnati. The album is narrated by Leonard 
> Maltin and focuses on Cincinnati's supposedly major role 
> in old-time radio broadcasts, including radio drama. There 
> were some old-time radio clips played, including calls of 
> former Reds announcer Red Barber (who used to host a 
> weekly segment on Morning Edition with "the Colonel" 
> before his death). Hopefully this piece can be tracked 
> down on npr.org. 
> 
> One of the points they made that was interesting was about 
> WLW's old 500kW signal. The old-time guys claim that the 
> 500kWs didn't extend WLW's reach (compared to the current 
> 50kW) so much as it strengthened the signal in its strong 
> areas. Dan and Garrett, I'd be interested in hearing your 
> thoughts on this, since in principle that sounds a little 

> fishy. I could see maybe not extending the signal *much* 
> (given the potential primitive transmitting technology of 
> the day) but I would still imagine the extra 450kW did 
> something to extend the station's reach. Also, they 
> mentioned the reason Crosley built a 500kW transmitter was 
> because the radios his company manufactured were really 
> weak (and basically cheap) and he needed a stronger signal 
> to compensate for it.