>> Unless KSLM recently changed, the old CE at Entercom told me that they >> dropped the KSLM power from 1 KW to 690 watts a long time back, but I >> don't remember the reason > >A power drop like that usually happens when a station switches to a >taller (and therefore more efficient) antenna. The actual field strength >of the station doesn't change at all.
The field strength on the ground doesn't change, but the close-in (<300 miles) field can change a lot. Taller towers have less high angle radiation, around 30-60 degrees elevation. This makes skywave much weaker nearby. That's one reason why stations with significant close protection requirements often go to towers of a half wave or so. More distant propagation of greater than 300-400 miles is enhanced, or at least the same as a shorter tower. A 5/8 wave tower has the greatest signal on the ground, but a secondary minor lobe at a fairly high angle develops. This causes interference between groundwave and skywave around 70 miles or so away. Many clear channel stations have settled on a height of 195 degrees, slightly over half wave as the best compromise. Local WHIM-1110 (now WPMZ) ran around 690 watts when they went to a 540' tower many years ago. It was considered to be the same coverage as their original 1/4 wave tower. And, WNBH-1340 has a tall tower, yet gets to put the full kilowatt into it due to grandfathering. Life is good! (grin) I have been waiting for some station at the top of the band to use a full wave tower in a directional array. This tower would have essentially no groundwave, but the close in skywave would be very strong. Combined with a common 1/4 wave tower, the directional array could null toward a station not far away without any ground nulls. It would be interesting to run a proof on that.. Craig Healy Providence, RI _______________________________________________ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
