Re: [IRCA] KSLM 1390 // KFXX 1080

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

>> 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




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