nsight On Rules #90
Blanketing Interference
by Harold Hallikainen
San Luis Obispo, CA - Another valuable resource is now available on
the internet. The full text of the Code of Federal Regulations
(including the FCC Rules) and the US Code (including the Communications
Act of 1934) are now available through the US House of Representatives
Law Library. The Uniform Resource Locator for the CFR is <http://www.pls.com:8001/his/cfr.html>
while the URL for the USC is <http://www.pls.com:8001/his/usc.html>.
Each of these includes a search engine where you key in a few key words,
and it gives you a list of likely sections. You can force it to search
for a particular phrase by surrounding the phrase by single quotes (').
For example, I used 'blanketing interference' to get the text of 73.318
for this article. Note that new resources are showing up on the net
all the time. You can find them by doing a search (using Yahoo or
Web Crawler) or by reading email mailing lists, usenet newsgroups or print
publications (like RW!).
In an unusual case of FM blanketing interference, the FCC the FCC revoked
the Program Test Authority for a new transmitter
site for a New York FM station (see 9 Fcc Rcd. No. 24, page 6873) in
July 1994. The station had to move back to its old transmitter site.
73.318
defines (for nondirectional FM stations) as that area within the 562 mV/m
contour as being subject to blanketing interference. After January 1, 1985,
any station that commences program tests, replaces their antenna or is
issued a construction permit for modification of facilities must satisfy
all complaints of blanketing interference received during a one year period,
starting when the new facilities are put into operation. Resolution
of complaints shall be at no cost to the complainant. These requirements
specifically do not include interference complaints resulting from malfunctioning
or mistuned receivers, improperly installed antenna systems, or the use
of high gain antennas or antenna booster amplifiers. Mobile receivers
and non-RF devices such as tape recorders or hi-fi amplifiers (phonographs)
are also excluded. Stations collocating with existing stations must
assume full financial responsibility for remedying new complaints of blanketing
interference for one year. Two or more stations collocating concurrently
assume a shared responsibility to remedy blanketing interference complaints
unless an offending station can be readily determined, and then that station
assumes full financial responsibility. Following the one year period
of full financial obligation to satisfy blanketing complaints, licensees
shall provide technical information or assistance to complainants on remedies
for blanketing interference.
136 of 139 Complaints Resolved
The station began program test operation in March 1990. The station
received 139 complaints of blanketing interference. All but
four had been resolved by March 1994. In inspecting the homes
of the complainaints, the FCC determined that one of the four
outstanding complaints was indeed resolved. The other three remained
unresolved.
Resolved Complaint
The station did quite a bit of work to eliminate interference at this residence.
A "master antenna", its mast, guy wires, and coaxial
lead-in cable were all replaced. A ground rod was installed.
An antenna rotor was repaired. FM traps were installed. Coaxial
jumpers between VCRs and televisions were replaced with 100% shielded cables.
The antenna lead-in on an FM tuner was replaced with coax. Ferrite chokes
were installed on all telephone and answering machine cables. The
station stated that they observed no difference in the operation of the
home equipment (televisions, radios, telephones, etc.) with the station
transmitter on or off. The FCC verified these results and also found
that the home owner's VCR was interfering with the AM radio next to it.
The FCC also determined that "static" and occasional interruption of telephone
calls was due to problems with the telephone company, not the radio station.
The home owner disputes these findings, claiming that reception on one
television channel is still not satisfactory, the VCR taping
and playback is not satisfactory, AM stereo reception is not satisfactory,
and her telephones were still not operating properly. The FCC, however,
decided in favor of the station. Operation of the consumer equipment
did not appear to vary between when the FM transmitter was on or off.
Unresolved Complaint - The New Neighbor
One complainant bought her house in the FM blanketing interference area
more than two years after the station began program
tests. As such, the station is not obligated to solve the blanketing
interference problems, but is obligated to provide specific information
on proper corrective measures. The FCC states the station "should
have provided... diagrams and descriptions which explain how and where
to use radiofrequency chokes, ferrite cores, Microwave Filter Company filters
and/or shielded cable." The station "should have recommended replacement
equipment that would work better in the high radiofrequency fields."
The FCC found that providing the complainant with copies of various FCC
Bulletins on interference was not sufficient. The complaint remains
unresolved.
Another Unresolved Complaint
The complainant lists 10 devices receiving interference. These are
four radios, a telephone, an answering machine, a cassette
player, a CD player, a VCR, and an "audio system". The station
replaced telephone wiring and equipment even though 73.318
specifically excludes stations from responsibility for interference
to devices that are not radio receivers. Although the station replaced
several of the radios (the homeowner refused the offer to replace some
of the radios), the FCC staff noted that on various radios in this home,
various numbers of additional FM stations could be received when the new
FM was off the air. This varied from two stations receiving interference
on one radio to 17 additional stations on another radio.
The FCC determined that "interference" to the complainant's telephone
was, as in the previous case, a telephone company problem.
Since these problems were present within the first year the station
went into operation and were still present four years later, the
FCC determined that the station did not comply with its responsibilities
under 73.318.
Interference to Telephones
The FCC points out that 73.318
specifically does not include interference to non-RF devices and that hard-wired
telephones are
considered non-RF devices. In addition, cordless phones are authorized
under Part 15 of the rules. 15.5(b)
states that cordless phones many not cause harmful interference and that
interference to cordless phones caused by the operation of an authorized
radio station must be accepted. Accordingly, the FCC ignored all
telephone interference complaints in this decision.
Defective Cows
One of the complainants was concerned about the biological effects
of the station's radiation on their health and on the health of
their cattle. He stated that since 1990 he has had several unusual
calf deaths and a calf was born dead with seven legs. The FCC found
that the radiated fields were lower than the ANSI standards, so it did
not consider this issue.
Rule Intent
The FCC points out that 73.318(b)
requires the station to satisfy ALL complaints of blanketing itnerference
which are received in
the first year of program test operation. This station had not
resolved them after four years operation. In the Report and Order
that
adopted the rules (see 57 RR 2d 126 (1984)), the FCC intended to have
applicants place blanketing interference high on their priority list when
choosing antenna sites. They did not expect stations to replace inexpensive
hand held radio with expensive FM tuners, but declined to include a clause
that would protect only receivers of good design and futher declined to
set receiver interference rejection standards.
The station's consultant pointed out that some of the complainants
would not be satisfied if there was any trace of interference to
any station, whether they listened to that station or not. The
FCC pointed out that station formats and listener tastes change with time,
so all stations must be protected, whether they are currently listened
to or not. The decision did not appear to take into account whether
a station receiving interference was protected from interference at that
location (protected from co-channel and adjacent channel such that a listener
could hear it if the blanketing interference was not present). It
might be unreasonable to protect someone from interference when they were
listening to a distant station far beyond its predicted contour, but in
blanketing interference questions, it appears such protection might be
required.
Station PTA Revoked
The FCC looked at the possibility of reducing the station's power to eliminate
blanketing interference. However, such a power
reduction would make the station not provide required coverage over
its city of license. The FCC decided to revoke the PTA and require
the station to utilize its previous transmitter site.
When I spoke with the station manager, he indicated the station is
currently operating from the previous transmitter site, and he'd
like to set the whole mess behind him.
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Harold Hallikainen is president of Hallikainen & Friends, a manufacturer
of transmitter control and telemetry equipment. He also teaches electronics
at Cuesta College and is an avid contradancer. He can be reached
at 805 541 0200 (voice), 805 541 0201 (fax), and on the internet at harold@hallikainen.com
and <http://hallikainen.com>