MITRE report on LPFM

[Aaron Read <aread@speakeasy.net>]

The MITRE report on 3rd adajcent protection regarding LPFM's came out 
today.  It says what we all suspected it would, and some things I didn't 
suspect.

The no-station-in-a-high-receiver-density-area is a weird one...I haven't 
run any math yet but it might preclude anything in the urban areas 
still.   Not that THAT matters...there's no way to get in the urban areas 
anyway; 3rd adjacent protection was not the problem there.

- Aaron

http://www.babel.serve.com/mitre/
(this clip is from MITRE4.pdf)

Page 5.3:

5.2 Recommendations
5.2.1 Operating Rules for LPFM
Based on the measurements and analysis reported herein, existing 
third-adjacent channel
distance restrictions should be waived to allow LPFM operation at locations 
that meet all
other FCC requirements, subject to the stipulations below.

• No LPFM station should be licensed within xmin meters of any location 
that is likely
to have a high density of receivers that lie within the FPFM protected 
area. The
quantity xmin is defined as:

         (HUGE UGLY MATH FORMULA THAT WON'T TRANSLATE TO EMAIL)

If the actual D/U ratio can be shown to be –15 dB or better (i.e., more 
positive) at
most locations in the area of high receiver density for a candidate LPFM 
transmitter
site, then the proposed site may be used, even if it is closer then xmin 
meters from the
area of high receiver density. This recommendation is believed to provide 
adequate
protection to RSVI as well all non-RSVI receivers.

• No LPFM station with an ERP of Peu dBW should operate within du 
kilometers of an
FM translator receiver on the third adjacent channel, where du is defined 
in 5.1.2.

• Any LPFM applicant who is allowed to operate at a smaller distance than du
kilometers from a third-adjacent-channel FM translator receiver should be 
required to
perform preliminary interference testing and then to pay for any necessary 
mitigatory
measures, such as a more selective bandpass filter for the translator receiver.

• The FCC should impose, for LPFM transmitters, a more stringent limit on 
third-
adjacent-channel emissions than the –35 dBc that CFR Sec. 73.317 (c) currently
allows at frequency offsets up to and including 600 kHz. The total energy 
emitted by
the transmitter in the third adjacent channel, in the form of phase noise 
spread across
the channel and/or discrete tones within the channel, should not exceed the 
level of
-55 dBc that was emitted by the LPFM transmitter used in the analog field 
tests.
However, the existing Sec. 73.317 (d) limitation of –43 dBW on discrete 
tones offset
more than 600 kHz from the carrier should not be relaxed.