[IRCA] KYMN

["Dan Strassberg" <dan.strassberg@xxxxxxx>]

George Sherman mentioned KYMN's former sign-off at Portland OR sunset
-----
I think the connection between KYMN's sign-off time and Portland sunset is
coincidental. Yes, there is a powerful and very old station (KOTK?) on 1080
in Portland, but, notwithstanding its age, the Portland station is not a
Class A; it is a Class B. Class Bs' sunrise and sunset times are not a
factor in determining the timing of mode changes of co-channel Class Bs or
of co-channel Class Ds with post-sunset authority. The timing of KYMN's
various operational-mode changes after Northfield sunset has got to be
related to sunset at one or both of the co-channel Class As, WTIC and KRLD.
KYMN is a Class D with a PSSA and nighttime authority as well. I am not
sure, but I believe that KYMN is (very slightly) east (as well as WAY north)
of KRLD. I am also pretty sure that KYMN is located outside of KRLD's
protected 0.5 mV/m 50% skywave contour. Therefore between Northfield sunset
and Dallas sunset (at least when Dallas sunset is later than Northfield
sunset), KYMN is probably allowed to operate with 500W ND. From the later of
Dallas or Northfield sunset until two hours after Northfield sunset, KYMN
must be permitted to operate at powers higher than 11W. The exact value
depends on the month, with higher values generally allowed in summer months
than in the winter. Then, at two hours after Northfield sunset, the power
drops to 11W year-round. There may be another step in there--higher power
(but lower than 500W) may be allowed from the later of Dallas or Northfield
sunset until one hour after Northfield sunset. I'm not sure of that,
however.

Anyhow, the rules for power reductions by Class D AMs with PSSAs are so
complex, they seem to me to be impossible to implement properly without the
use of computer control. And when the FCC first promulgated those rules,
computers were not all that pervasive. So maybe the idea was to mollify the
daytimers on Class A channels by granting them post-sunset authority but to
make the rules so onerous that nearly all of the affected stations would
say, "we can't do this, and the small power provides so little coverage that
trying isn't worth the effort." Then computers became widely available at
low cost and the rules seemed less onerous.

--
Dan Strassberg, dan.strassberg@xxxxxxx
eFax 707-215-6367










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