[BC] Poor Reception Areas

[Warren Shulz]

The problem is to convert F(50,10) FS levels expected at 30-feet above
average terrain  into recovered signal level into a receiver with a
random pickup wire antenna at ground level.  Pickup antenna could be
walkman headphone cordage, line cord antenna or wire folded dipole.  Add
into that building material absorbing, reflections, and only then could
you estimate  the possibility of reception performance.  

I think the DTV folks fought this battle with indoor DTV antennas.  A
DTV STB needs 15 uV to light up. But if signal has reflections you will
get a mutes and pixilation's.  In analog you get a noisy signal or no
reception. 
Unless you have a cryogenic preamp these are real world limits of the
receiver performance.

Few if any consumer is willing to connect their FM receiver to an
outdoor antenna.  Yet, the design spec is a receiver antenna elevated
30-feet above terrain.

Warren Shulz
WLS CGO

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

 From: Dippel, Don

Hello All and thank you for your input. I think Dana has it right about
the interference factor being the most important.

I have been running V-soft's Probe for years and know about the
contours, especially using Longley-Rice.

What started my thoughts was the NPR survey. They said 75% of listeners
were in the 60 Dbu contour. 12% in the 50 dbu, 6% out to 40 dbu and 6%
beyond the 40. But my question was, is it safe to assume the average
home could get reception if it was within the 50? Or may the 54? Maybe
there is no reasonable answer.

I do appreciate the responses because they help me to think this
through.

Don Dippel
Chief Operator WPCS
RBN Engineer

 

-----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

>45-50+ 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.