[BC] FCC Approves proposed AM MoM Rules

[Mike McCarthy]

In this specific portion of the text, I'm referring to a very small part of 
the overall measuring/validation process of arrays which can follow the 
strict procedures defined.

Yes, there are numerous other tests done to the towers at varying stages. 
This ONE specific measuring condition will catch MANY engineers off guard 
as the traditional practice has been to analyze the base impedance at the 
TCT/output J plug with everything PERMANENTLY connected.  Installation 
practices and equipment selection will need to be adjusted so as to permit 
easy and quick disconnection of EVERYTHING (including the feed point) to 
achieve a pure floating tower with minimal work required, to then reconnect 
in an equally fast and simple manner. YET, still achieve the best end 
product which will survive long term AS WELL AS to allow for repeated 
iterations of the same measurements for later maintenance or troubleshooting.

This disconnection/isolation condition will also become an important tool 
in the diagnostic process when there are problems down the road.  One of 
the first questions asked will be. "Does the self-impedance of the tower 
match/closely approximate that of the validated model?"  If not, that's the 
first place to start looking.  The "bad tower" will show a significant 
departure from the validated data.

Granted, it's not that common of an occurrence for a tower to show 
"bad".  But the loss of johnny balls or a transmission line bond are but 
two examples of where that level of definition will provide a useful level 
of information to quickly track down problems.  remember times where you 
didn't know what the base impedances were when you were searching for a 
problem?  Well, this process eliminates that headache.

The reason for such a strict "rule" is simply the modeling software doesn't 
factor in complex loads which jump the base.  The  impedances of the 
various devices crossing the base of any given tower are too dynamic for 
the programs to consider.  So the it was concluded the only means to insure 
validation is to confirm without any question the tower being measured 
first matches the model as a lone simple free space radiating object. Then 
add the various loads (feed point conductor, static drain, lighting choke, 
iso-coupler, bazooka feed, etc.) to the tower and then ADD in the "fixed" 
loads between the tower base and sample TCT to the total model.

This is done on each tower in the array.

The above also presumes the issues of mutual coupling and such and are also 
factored into the mix.

With all of the above said, it will be VITAL to record as much measured 
data as possible at all stages of the array.  In addition to defining the 
self impedance without anything connected, define it at the base J plug and 
ATU input under varying conditions and modes, such as NDA, etc., to provide 
diagnostic data later.

The treast for the process is better suited for a sit down seminar or 
demonstration than a list exchange.  The NAB's seminars last year covered 
this is some detail.  In speaking with Ron Rackely, this year's seminar 
will focus more on the application of the new rules as well as the process 
of designing and implementing. If you have any interest in learning the 
process and don't have a DA in the works, that's the best place to get the 
run down in a compressed format in the near future. Otherwise, get with 
someone who will be building one.

I would argue this could be easily one, maybe two college level courses for 
a complete and proper treatment of the subject and processes.

Like solid state replacing tubes, this process will be the same type of 
paradigm shift for AM arrays.

MM

At 08:06 AM 9/28/2008 -0400, WBRadiolists at aol.com wrote
>In a message dated 09/27/2008 8:34:53 AM Eastern Daylight Time,
>Towers at mre.com writes:
>
> > Keep in mind that when there is a problem, the same disconnection aspect
> >  will be needed to verify out the tower's self impedance.  This is a
> >  critical measuring tool. When you have transmission lines on the tower as
> >  if there is a problem with an outer conductor bond to the tower or a
> >  shorted Johnny ball, one will see a fairly substantial shift in the self
> >  impedance. So it's vital the tower be fully floating and isolated as much
> >  as practical.
>
>Please forgive the "stupid questions" here...
>
>If you measure the tower as though it's completely unloaded, then use that
>for the modelling software... does it not then throw the modelling out the
>proverbial window as soon as you reconnect all of that other "stuff"?
>
>Would it not make sense to measure and model it both ways, so that you can:
>
>a) see the difference, and
>b) see what it will do in reality?
>
>Willie...