[BC] Directional Antenna Proofs

[James B. Potter]

Mike:

Thanks for your remarks.  I have considered the likelihood that the ground
radials have corroded.  At this point, I encounter numerous theoretical
contradictions and discussions of experience and 'good practice.'  One
school holds that copper oxide corrosion on the copper ground wires raises
the contact resistance between the wires and the soil in which they are
buried, and therefore this is a negative situation because it impedes ground
conductivity.  Another school holds that the 120 radial counterpoise is
sufficient as a standalone entity irrespective of any contact resistance
with the adjacent soil, and it doesn't matter if those wires are green.
Clash of ideas here.  

Then, there is the 'urban legend' that AM propagation from older stations
can be significantly enhanced by truckloads of conductive soil overlaid on
the ground field.  Several respectable engineers have opined that.  But, in
contradistinction, the great Laport of Radio Antenna Engineering book fame
(for those who don't know, this is the Bible of Bibles for antenna theory
from 1954) writes the very opposite -- that conductive soils dissipate the
RF from the counterpoise and destroy the signal.  

OK, now what?  Our 'soil' around the Ozarks is pure rock consisting of
calcium carbonate and iron.  You can't push a spade into it more than 1
inch.  You need a auger or backhoe to dig a hole for a rose bush.  That's
what we live with around here. But, as can be seen from those excellent
Jules Cohen design reports and initial proofs, the signal from that array
went far afield when it was new vs. now.  The tower joints are welded. Does
broadcast engineering get any more fun than this?  It's the emails and phone
calls from disgruntled listeners that keep me awake at night.  And these
aren't nut cases, they are mostly seniors who go back decades and 'remember
when' KWTO got all the way down south to Arkansas.  Now, it hardly hits
Branson reliably -- 50 miles north of Arkansas. 

Dave Dybas in another post cited noise in the band.  I certainly concur
about that.  On another blog a few years ago some guys were lamenting the
amount of digital grunge introduced by iBOC digital AM around the country,
e.g,, the San Francisco area.  Could that be the problem?  And all the
bloody microprocessors we all have in our homes.  In my house, I can trace
AM band grunge to such sources as the four computers, electroluminescent
clock radio displays, the two satellite dishes on the roof, and the
controller for our septic system.  What the heck ever happened to Part 15
cert for unintentional radiators?  I doubt of any computer ever met the FCC
radiation spec. And when the power fails as it does every few months, it
gets REAL quiet on AM battery portable.  So, it is probably true that the
ambient noise floor has risen over the decades with the advent of
microprocessors in every darned appliance including the toaster and the
toilet.  You can add cable TV leakage, too.  So is that what I tell Sharon
and Debbie as the reason they can't hear Rush?  Nobody's going to buy the
computer explanation, including me. 

Ron KA4INM, cites increased an increase in utility voltage as another
source.  I've seen that, too.  Somebody should climb those towers with a
pocket full of .01 disc ceramic bypass caps and.... 

All advice gratefully accepted, folks.  Much obliged. 

Thanks/Regards/Jim 

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

 From: Mike Vanhooser

If it is that old the problem could be ground system deterioration.  Just
because the numbers are right doesn't always mean anything.  I have had a
station recently with all the numbers right on, and half the ground system
missing (thank you copper thieves).  If you don't have a complete
counterpoise which is not corroded, and good grounding at each tower
(radials alone will not always give you a good ground), then coverage is
going to degrade.  A station which is 40+ years old can generally benefit
greatly from a new ground system.  I know theory doesn't support this, but
reality does.

>On 20 Jun 12 9:11 PM, James B. Potter wrote:
>> I just started at a 5-tower
>> directional 560 station with DAD and DAN patterns, and the coverage 
>> is significantly lower than when this system was originally installed.