On 8/3/2012 9:49 AM, Tom W8JI wrote:
> This illustrates the danger of non-peer reviewed technical articles. I
> personally know of at least a half-dozen AM BC stations that invested
> money in converting to folded unipoles, and a company in Texas started
> producing antennas based on that silly idea.
> http://www.w8ji.com/radiation_resistance.htm 73 Tom
If I appear to be a bit snarky in my rejoinder, nothing personal, its
really my style.
Both Kintronics and Cortana manufacture kits for AM station and they are
they a being used by radio stations all over the world. In can only
agree with Tom to the point that what may be silly is any claim that the
expectation of converting to a folded unipole by it self increases
radiation efficiency was wrong. That notion was dispelled long ago and
presented in a paper at the 1996 NAB technical session by a leading
broadcast consultant group deTreil, Lundin, and Rackley (www.dlr.com)
I did a summary of their study which I posted here in 2003 and back in
2006 (Jan 4, 2006 Top-band: Shunt fed tower question?)
I pointed out that the DLR study concluded both by NEC 4.1 analysis and
exhaustive field tests on 1600 Khz with an actual tower, with and
without being grounded, and with a cage feed did *not* improver FS,
radiation efficiency, or exhibit any better performance over a poorer
ground system. So why are broadcaster still buying them. Let me try to
explain from my marketing and hopefully practical perspective.
Today the concept of a folded unipole, once you eschew the original
hype and understand the limitations, is far from a "silly idea". I
think Tom suggests that "peer review" would have prevented this from
happening. Yet the antenna design and continued production of these
feed kits appears not to be based on stupidity , but based on a
principle that often will trump "peer review" and that is an idea that
has been supported by market forces and a customer base market that pay
for it and support it, it will continue beyond negative peer review, and
press on regardless.
Today with limitation and restrictions on towers more and more facility
co location is evident. Having a shirt fed grounded 300 foot tower is a
gold mine to broadcasters, especially day timers that could only make a
dime when the sun was up. An insulated base AM tower required
iso-couplers, some very expensive for high power FM, to take advantage
of your real estate. I know of station owners who make today more
revenue from cell service, pagers, two way radio, and other stations
then they do from their format. its all about location, location,
location and if you have one the idea of having a skirt fed antenna is
not "silly" but profitable.
Most topbanders know what an the cost of insulated base for a Rohn 45
is and savor the chance to run other feed lines inside the tower for a
variety of other antennas, rotor cable, and the like, and how a cage fed
tower unipole makes that possible. Such a consideration should also
carefully compare the destruction of a lightning strike to associated
equipment from a grounded tower to one that is not directly grounded.
For sure I know this has nothing to do with E and H plane radiation
loses or trying to manipulate Maxwell's equation, but it sure does have
something to do with your pocket book when it comes to replacing
equipment damaged by a 140 foot free floating lightning rod compared to
a grounded lightning dissipation array, if I dare to call my unipole that.
Tom was right that the initial 'brag" was not peer reviewed and false
assumptions were made. Yet the final result over the years a "silk purse
has been made out of a sows ear" contrary to what the old time farmer in
Iowa used to tell me. So what have we learned from all of this?
Never let peer review get in the way of market forces causing you to
throw the baby out with the bathwater.
Herb Schoenbohm, KV4FZ
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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