Joe Nicholson wrote in a message to Roy J. Tellason:

 -=> Quoting Roy J. Tellason to Joe Nicholson <=-

RJT> That, and the fact that early tv sets weren't as selective
RJT> in their front ends as later stuff was.

JN> Yep, I remember servicing a hundred brands in the 50's and
JN> early 60's.  The "good" stuff like Philco and Packard Bell
JN> had individual oscillator tuning to tweak the channels.

JN> Cheapies on the market like Sears and Mad Man Muntz had a single 
JN> high band and a single low band oscillator adjustment. They were 
JN> absolutely crap - 1 or 2 IF stages vs 3 or 4 used by the high-end 
JN> brands.

I guess there's always been cheaper stuff out there,  I just never took
notice of it all that much.

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

RJT> Are these only in specific locations,  or what?

JN> Right, only specific locations.  At the time I was studying 
JN> electronics and preparing for my FCC license, St. Louis and SoCal
JN> were the two areas that were most noteworthy/prominent.

And they're consistently there?  Are these things mapped? 

RJT> I can still remember some black-and-whites out there in the late 
RJT> 1960s that had those big whip antennas bolted to the rear bumper.  
RJT> Don't remember who was using them, though.

JN> And the "secret" undercover cars used regular AM car antennas 
JN> welded/soldered to a specific lenghth.  But I could hear the 
JN> dynomotor a block away.  That always gave them away to a sharp 
JN> ear.  

Heard of those things,  never actually saw one,  though.

JN> He hadn't realized they were old, old, old 2490kc AM receivers and 
JN> 72-75Mhz FM transmitters and were worthless to hams (or anyone 
JN> else).

RJT> Hm.  No way to easily modify that stuff, eh?

JN> Can't modify AM transmitters to FM, nor FM to AM,

Yeah,  I guess that would be a bit much.

JN> and the frequency spread prohibited tuning them to the ham bands.
JN> Someone here recently questioned converting a scanner, 154Mhz to 
JN> 174Mhz, to the FM band, 88Mhz to 108Mhz.  Not only is the frequency 
JN> spread too great for the conversion but the standards for FM 
JN> broadcast and PS transmissions are totally different.

Yeah,  I'm aware of the difference in deviation.  I'm not clear enough on
the circuit design issues involved in that stuff to know how they're
different, though.  I used to have a bit of difficulty with that stuff in
my textbooks way back when,  it may be time for another look.  Maybe I
oughta drag out my copy of "Practical Radio Communications" or
whatever that title is.

JN> Sidebar:  Motorola, GE, RCA manufacture radios for (about) 130Mhz 
JN> to 150Mhz (military frequencies used for on-base law enforcement, 
JN> military fire departments, etc), and those companies also 
JN> manufacture radios in the 150Mhz to 174Mhz range (civilian 
JN> forestry/police/fire/taxi/railroads, etc).

JN> Even with that smaller frequency difference, a radio in one band 
JN> cannot be tuned to frequencies in the other band. The "front ends" 
JN> of each are totally different.

That different?  I wonder if they use the same boards...

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