-=> Quoting Phil Marlowe to Leonard Erickson <=-

 > How far away are these stations? Any idea where
 > their *transmitters* are?

 PM> I'd guess less than 100 miles? Probably around
 PM> 50-60.

 When the FCC was passing out station licenses in the late 40's
 through the 50's, the theoretical maximum distance for channels
 2-6 was 100 miles, and for channels 7-13, only 50 miles.  That's
 the basis for not assigning same channels and adjacent channels
 within so many miles of each other. (note: channels 4 and 5 are
 not adjacent, thus 4 and 5 both are licensed in Los Angeles.)

 Well, lo and behold, people in San Diego were receiving L.A.'s
 channels, and on good days even channel 3 which is 215 miles away
 in Santa Barbara.

 Someone had not taken into consideration inversion layers which
 exist over some portions of the U.S.  They act as ducts, funneling
 signals hundreds of miles away.

 (I have watched a channel 2 out of Texas after channel 2 in L.A.
 went off the air at night.)

 Most public service (police/sheriff/fire) was dispatched on 2490kc
 and the mobile radios were transmitting somewhere in the 4Mhz gap
 between channels 4 and 5 -- and causing quite a bit of interference
 on TV.  But the FCC stuck by its guns and said San Diego was beyond
 the range of L.A.'s stations and they were not guaranteed to be free
 of interference.  (SDPD was the last agency to leave 2490, in summer
 1962.  Everyone by now was on either lo-band or hi-band VHF.)

 Armchair cops could receive dispatch on their AM radio by tuning to
 the image frequency, and hear the units in the field by tuning a TV
 to either channel 4 or 5.  (TV and mobile units both FM)

 Sidebar: In summer 1973, I spent 90 days active duty as a reservist
 at NavyMARS in San Diego.  During that time, we received thousands
 of LAPD mobile radios which the RMC "thought" could be used by MARS.
 He hadn't realized they were old, old, old 2490kc AM receivers and
 72-75Mhz FM transmitters and were worthless to hams (or anyone else).

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