102.5 to Spanish? Nahhh.....

Dan Strassberg dan.strassberg@att.net
Sun Dec 18 16:22:47 EST 2005

I'm still missing something. I get your explanation of the rule, Scott, but
if I'm right about the source of the interference to the stations 10.6 and
10.8 MHz below the interfering station, the rule does absolutely nothing to
solve the problem. I guess the rule must not be directed at radiation from
the LOs of receivers as I had thought but rather at the LO frequency falling
within the passband of a station you are trying to tune in. Or maybe the LO
in FM receivers runs 10.7 MHz ABOVE the station the receiver is tuned to. I
rejected that possibility out-of-hand because that would put the LO for
stations above 97.3 in the aircraft band that starts just above 108. I
didn't figure that would be safe because radiation from LOs could interfere
with transmissions in that band and cause planes to crash. But maybe the FCC
isn't worried about radiation from FM receivers--except maybe receivers
carried onto planes by airline passengers.

Dan Strassberg, dan.strassberg@att.net
eFax 707-215-6367

----- Original Message -----
From: "Scott Fybush" <scott@fybush.com>
To: "Dan Strassberg" <dan.strassberg@att.net>; "Garrett Wollman"
<wollman@csail.mit.edu>; <bradfordwood@comcast.net>
Cc: "boston Radio Interest" <boston-radio-interest@rolinin.bostonradio.org>
Sent: Sunday, December 18, 2005 3:20 PM
Subject: Re: 102.5 to Spanish? Nahhh.....

> At 02:31 PM 12/18/2005, Dan Strassberg wrote:
> >What am I missing? 102.5-10.7=91.8. Is 102.5 prevented from moving to the
> >Pru by WUMB in Quincy and various low-power 91.7s that ring Boston?
> Yup.
> Section 73.207 of the FCC's rules sets out the table of spacing
> requirements for FM channel separation, and it includes spacing rules
> for stations 10.6 and 10.8 MHz distant. In the case of a class B
> signal like WCRB, it must maintain a 15 km separation from a class A
> facility like WUMB. (The spacing requirements vary, from 10 km
> between two class A stations to 48 km between two class C stations.)
>  From FM128 to WUMB in Quincy is 17 km. From the Pru to WUMB is 10.9 km.
> The FCC does not waive the IF short-spacing, nor does it allow the
> use of directional antennas or terrain-based contour protection to
> alleviate IF short-spacing as it does with other short spacings.
> Channel 5 isn't an issue with regard to WBOS, since 82.2 is outside
> channel 5's spectrum. (It's in channel 6.) The only potential
> conflict that the FCC recognizes between low-band VHF and FM is
> between channel 6 (with audio carrier at 87.75 MHz) and stations on
> 98.5, and there's a chart of allowable spacings for such stations on
> the FCC website. (In one notable case a few years back, KUPL-FM in
> Portland OR moved from 98.5 to 98.7 to allow it to move its antenna
> to the same ridge as KOIN-TV 6.)
> The FCC spacing charts are at www.fcc.gov/mb/audio/spacing.
> s

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