[BC] Poor Reception Areas

[Warren Shulz]

Important to note these FCC predicted levels are for a reference dipole
elevated in the clear 30-feet above terrain.  Pulling down to ground
level cost at least 10 dB or more of signal level.  Add in reflections
from objects (include metal vertical street light poles) and the
received field is a field reflective wave fronts.

I actual mobilized a rig in the 80's in the flat lands of IL and in many
cases we seen the performance levels as predicated.  Local reflections
would create a stand wave oscillation of the FS reading as we recorded
levels on a chart recorder over a 200-ft span.  After that experience  I
concluded real world field measurements at best were an inaccurate
science.  Antenna performance must me measured on a test range, except
in the most obvious problems.  

Example, is a Willis(Sears) Tower DTV UHF station mounted a directional
antenna with the main lobe directed into the tower structure.  A design
error in the brackets rotated the antenna 180 degrees so the null was
facing away from the mounting structure.    In that case field readings
confirmed reception reports of a problem.

When its said and done its amazing you get any reception of a usable
signal in an urban area. Driving city streets in an automobile with a FS
meter and 1/4 -waver vertical the RF levels will vary +/- 10 dB (or
more) in an urban area.  

Warren Shulz 
WLS CGO

-----Original Message-----

 From: Urban, Brian L

70 dBu (dB above 1 uV) = 3.16 mV/m
60 dBu (dB above 1 uV) = 1 mV/m
57 dBu (dB above 1 uV) = 0.7 mV/m
54 dBu (dB above 1 uV) = 0.5 mV/m

The engineering charts in 73.333 are used to predict received signal
strength; F(50,50) for desired signals, F(50,10) for interfering
signals.

     The F(50,50) chart gives the estimated 50% field strengths exceeded
   at 50% of the locations in dB above 1 uV/m. The chart is based on an
   effective power radiated from a half-wave dipole antenna in free
space,
   that produces an unattenuated field strength at 1 kilometer of about
   107 dB above 1 uV/m (221.4 mV/m).

The F(50,10) interfering signal curves are 50% of locations 10% of the
time.  Those curves are based on actual measurements made in the early
days of radio.  If you have ever tried to take FM field strength
measurements, you know what a crock of bull those curves actually are.
See 73.314 for the accepted procedure.  Check your credulity at the
door.

--
Brian Urban
Chief Operator
KUT Radio
TEL 512-471-1085

On 2/22/10 4:19 PM, "Jason R. at KGVL - KIKT"
<jyrussell at academicplanet.com> wrote:

>45-50+ is pretty low, and you'll start getting trash and picket fencing
as
>you drive along.
>60+ works, but you'll start noticing some noise in the signal.
>I *think* 70 dbU is a city - grade.  Gets inside most businesses with a
>useful signal.
>80+ ish oughta sound pretty decent.
>90+ should drive a receiver into quieting.