[BC] FCC Approves proposed AM MoM Rules

[RichardBJohnson at comcast.net]

It has been my experience that most directional
antennas were pretty straightforward as designed
because early tools didn’t allow much innovation.
Don Howe used a slide-rule, graph paper, and a
polar planimeter.

The bandwidth problems usually remain implementation
problems. For instance there are arrays that use high-Q
series-tuned circuits for phase adjustment while the phase
should have been obtained using transmission line lengths
with slight tweaking available with a low-Q “tee.”

Or, instead of building out a common-point as the common
connection of input “l” sections, the typical “Gates" design
used a high-Q “tank” circuit with taps.

Looking at the Kintronic equipment at the most recent
NAB show, I observed that more modern, less frequency
selective, circuits were being used. Reasonable pattern
bandwidth should be obtainable, even if the towers are
close coupled and have high mutual impedances, a
condition which, in the past has been blamed for poor
bandwidth.

I have read technical discussions about using
independent transmitters for each tower with modulation-
frequency-to-rf phase variation to compensate for sideband
distortion in the nulls. What seems to have been lost in
that discussion is that the problem in the nulls would just
get moved to the main lobes so it is not a solution at all.
The solution for broad bandwidth is to use broadband
circuitry which means towers not too short, not too tall,
and no high-Q circuits.

Until such redesign, IBUZ will be useful for daytime-only, non-
directional sites and you can bet your bippie that the rule-
changes come about because somebody has discovered
just that.

--
Cheers,
Richard B. Johnson
Read about my book
http://www.LymanSchool.org


 -------------- Original message ----------------------
From: dynotherm at earthlink.net
> While pattern b/w may be potentially improved using modeling tools,
> alteration of AT LEAST operating parameters will be necessary, and
> frequently radiator relocation/array reconfiguration will be the
> main requirement.
> 

[Snipped...]