[BC] FCC Approves proposed AM MoM Rules

[Mike McCarthy]

He's right for the most part.  When the array is designed using MoM and is 
tuned using the same, you are within a few degrees and % of the final 
numbers almost always.  The last array we did which was designed using MoM, 
but used a non-MoM sampling system tuned up in less than 8 hours from 
arrival to on the air at full power.  We then ran 10 mile radials to trim 
the nulls down to the desired depths.

We spent more time matching lines and adjusting the phase rotation than 
actual pre-tuning.

That said, the new MoM procedures are extremely precise and will require a 
deviation in standard construction design, assembly procedures and practices.

One of the most significant will be the ability to disconnect EVERYTHING at 
the base of the tower --easily and quickly--- to make floating 
self-impedance measurements.  The measurements MUST be made at the base 
flange connection point and not through the feed point bowl where the 
sample toroid would be located. The feed point conductor must be 
disconnected at the tower base. Same too for any transmission lines which 
jump the base from an isocoupler inside an ATU or on the ground side of a 
line loop. (NOTE...any FM's on the tower will need to shut down for this 
series of measurements.) All those will too need disconnection and be tied 
off the to tower without any loops. Anything hanging from the tower between 
the base and the ATU usually adds a few ohms of reactance and 
resistance.  On a low impedance tower, those few ohms could substantially 
contaminate the measurements.

So....it looks like a junction  box at the base of the tower will now be 
needed for the towers lights and other controls IF one runs the conductors 
through the feed point and conduit.

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.

It certainly makes the mechanical design, construction, assembly, and 
initial part of the tuning process a bit more complicated.  But the end 
result is no walk-in's.  And less time spent planing and running radials on 
a power and pattern which might be substantially less than the day 
operation. On a 50 day, but 1KW night, that's not running walk-in's at 250 W.

MM



At 10:46 PM 9/26/2008 -0400, Cowboy wrote
>On Friday 26 September 2008 09:26 pm, Craig Healy wrote:
>
>
> >  Don't get me wrong, if this actually works - and can be PROVEN - then I'm
> >  all for it.  I just would want some hard evidence that it's as good as is
> >  hoped.
>
>  Having worked on both, I can tell you that the MoM arrays are almost
>  just a set and walk away deal.
>  Almost. VERY almost.
>  This by running a conventional proof on a MoM array.
>  It was in, we just wanted another percent or two margin.
>
>  Initially, I was skeptical, and for the same reasons many have mentioned.
>  Experience shows the skepticism was greatly exaggerated.
>
>--
>Cowboy