[BC] Pre 1960 radios...

[Mike McCarthy]

It's all contour protection.  We have 1570, 1580, 1590 and 1600 in the same 
market.  In fact, two 1600's exist at opposite ends...for now. We also have 
1200, 1220, 1230 and 1240 as well as 1280 and 1300 all in the same 
market.  We also have a 15KW 750 sandwiched between 720 and 780 (each 
50's).  Granted the 750 TX is some 70 miles from the 720 and 780 tx's, it 
still puts a 5 mV over the whole metro while not overlapping the 25mV contours.

With that said, many of these stations were built before the FCC modified 
it's day spacing rules in the early 80's.  When the FCC did that, all kinds 
of new stations popped up in areas which didn't have room before.  Most of 
them on Class A channels. (Since that rule change, we added 750, 1030, 1080 
to the market)

If the commercial FM band operated the same way as the non-com part (which 
follows the same contour protection only principal as AM), we'd have 
another couple hundred or a thousand minimum Class A stations on the air 
all over the place.

MM

At 08:03 AM 9/1/2008 -0400, r.j.carpenter wrote

>My National Criterion (NC-1000) "binaural" AM/FM tuner has a "10 kc" notch 
>filter in the AM section. There is a single slug-tuned coil. While I have 
>the circuit diagram, I can't find it right now.
>
>
>I thought the FCC had a rule prohibiting stations closer than 30 kHz 
>separation in the same area.  It must have something to do with field 
>strength, since we have 1580 and 1600 on opposite sides of DC.
>
>bob carpenter