FM Blanketing Interference

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FM Blanketing Interference: A Case Study of Problemsand Solutions for a Typical High Power FM Station

Thomas M. Eckels, P.E.

Hatfield & Dawson Consulting Engineers, Inc.Seattle, Washington

ABSTRACT

FM broadcast stations in urban areas often operate fromtransmitter sites which are either surrounded by residentialdevelopment or are being encroached upon by residences.Within the area close to a high power FM transmittingfacility blanketing interference is very likely, affectingradios, television sets, and other consumer electronicdevices exposed to the high field strength levels producedby the transmitter. This paper describes the FCC’s rules andpolicies with respect to blanketing interference, the kinds ofconsumer electronic equipment typically affected byblanketing interference, the types of interference producedwithin the blanketing contour, and the technical and “publicrelations” measures which have been effective inameliorating the effects of blanketing interference.

INTRODUCTION

Blanketing interference is a general term which refers to theinterfering effects of very strong AM, FM or TV signalsproduced in the vicinity of a high power transmitter. One ofthe symptoms of blanketing interference is the disruption ofthe normal operation of radio and television receivers by astrong signal, which blocks the reception of other signals--hence the term “blanketing”. As the term has come to beapplied in specific cases, it actually describes severalspecific types of interference mechanisms which occur inthe presence of a high level of radio frequency energy.These include: receiver front-end desensitization,production of intermodulation and other spurious productsin receiver front-ends or in non-linear junctions (power andphone lines, chain link fences, tower members, etc.) near thetransmitter; and rectification and detection of radiofrequency signals in audio circuitry. The interferenceproduced in the blanketing area can affect a wide range ofelectronic devices normally found in residences, includingtelevision receivers; AM, FM and shortwave radios; stereoand “home theater” equipment; intercoms; telephones (bothwired and wireless), and computer equipment. Blanketinginterference can both prevent the reception of desired radio

and TV signals and cause undesired signals to beintroduced into home electronic equipment (e.g. broadcastaudio on a homeowner’s telephone).

The typical blanketing interference problems andsolutions described in this case study were drawn fromthe author’s experiences in resolving blanketinginterference complaints for Non-Commercial FM stationKVTI(FM), Tacoma, Washington.

FCC RULES AND POLICIES

The FM Blanketing Rule

The present FM blanketing rule, §73.318, was adopted inOctober 1984, by Commission action in Docket 82-186;the rule became effective January 1, 1985. The pertinentpart of the §73.318 reads as follows:

(b) After January 1, 1985, permittees or licenseeswho either (1) commence program tests, or (2)replace their antennas, or (3) request facilitiesmodifications and are issued a new constructionpermit must satisfy all complaints of blanketinginterference which are received by the station duringa one year period. The period begins with thecommencement of program test, or commencement ofprogramming utilizing the new antenna. Resolutionof complaints shall be at no cost to the complainant.These requirements specifically do not includeinterference complaints resulting frommalfunctioning or mistuned receivers, improperlyinstalled antenna systems, or the use of high gainantennas or antenna booster amplifiers. Mobilereceivers and non-RF devices such as tape recordersor hi-fi amplifiers (phonographs) are also excluded.

For purposes of administrative convenience, §73.318 (a)defines the area within which blanketing interference willbe assumed to occur as the area within the 115 dBu/mcontour. A licensee’s financial responsibility for theresolution of complaints applies only to those

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complainants who reside within the 115 dBu/m blanketingcontour. Following the one year period, and forcomplainants who reside outside the blanketing contour,station licensees are obligated to provide “technicalinformation or assistance to complainants on remedies forblanketing interference”.

FCC Response to Blanketing Complaints

Over the past several years, the Commission has becomeincreasingly assertive in its enforcement of the FMblanketing rule, largely in response to complaints fromneighbors who have been affected by the operation of newFM facilities in locations where high power transmitters didnot previously exist. In at least one case, the neighborsretained legal counsel in Washington to represent theirinterests before the FCC.Two recent cases illustrate the importance of resolvingblanketing interference problems and the potentialconsequences of an inadequate response to blanketinginterference complaints. In Calvary EducationalBroadcasting Network, Inc., an FCC Administrative LawJudge imposed a one-year license renewal term,accompanied with strict compliance and reportingrequirements, on KOKS(FM), Poplar Bluff, Missouri. Thisaction was later affirmed by the Review Board (9 FCC Rcd,6412, 11/2/94). In the case of WRQI(FM), South BristolTownship, NY, the Commission staff ordered the station toabandon its construction permit site and to move back to itsoriginal licensed site. The station had operated from the CPsite for four years and had not resolved all blanketinginterference complaints to the satisfaction of either theneighbors or the FCC during that time.

Consumer Equipment Covered by §73.318

There are ambiguities in the language of §73.318 whichleave open to question the specific types of consumerelectronic equipment included in the blanketing station’sarea of responsibility. “Mobile receivers and non-RFdevices” are specifically excluded by §73.318, but one mustlook to the Commission staff’s actions in specific cases todetermine how these exclusions will actually be applied.Based on the record in the KOKS(FM) case and on theCommission’s official correspondence with WRQI andKVTI, it appears that any piece of equipment whichcontains a radio or television tuner and which is capable ofbeing plugged into an AC outlet is considered to be coveredby §73.318. This includes “boom boxes” and other portablestereo systems which may also operate from battery powersupplies.

Telephones - Telephones, both hard-wired andwireless, are not protected under §73.318. In a letter to the

legal counsel for WRQI (1800B#-MJF/RDG, July 14,1994), the Commission staff’s position with respect totelephones is very clearly stated:

Hard-wired telephones are considered non-RFdevices under §73.318 and as such are not coveredby this rule. Cordless telephones are covered byPart 15 of the Commission’s Rules. Section 15.5(b)states, in pertinent part, that cordless telephones maynot cause harmful interference and that interferenceto cordless telephones caused by the operation of anauthorized radio station must be accepted. (P. 16)

RF Devices with Non-RF Components - Withrespect to devices which contain both a radio receiver anda tape recorder (a common configuration for “boom-boxes” and modern component stereo systems) it is notclear from the record what the requirements of §73.318are with respect to the tape recorder. Has the stationsatisfied the requirements of the rule if the radio portionof the unit functions normally? As a practical and“political” matter, apart from the question of compliancewith the rule, it is clearly in the station’s interest toresolve the interference to both the radio and the tapeplayer.

VCRs and Camcorders - According to the current

edition of FOB Bulletin No. 16, FM Interference to TVand FM Radio Reception, March 1991, VCRs are notsubject to the requirements of §73.318:

You can sometimes hear FM radio signals ontelephones and other home electronic entertainmentequipment, such as Video Cassette Recorders(VCRs), stereos, and recording devices. TheCommission offers no interference protection forthese devices. Therefore, you should contact yourdealer or manufacturer for assistance. (Page 4)

However, in both the WRQI and KVTI cases, theCommission staff has considered VCRs to be protectedunder §73.318. Therefore, based on the more recentinterpretations of §73.318 by the Commission staff, VCRsare subject to protection. Camcorders are specificallyexcluded from protection under §73.318, according to theCommission’s correspondence with KVTI.

Technical Information and Assistance

The technical information and assistance provided toresidents outside the blanketing contour and those whocomplain after the one-year period must be specificenough to allow the complainant to understand how toresolve blanketing interference problems to specific

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equipment (i.e., how to install filters, ferrite cores, etc.). Inthe event that the corrective measures are not successful, thestation must recommend replacement equipment which isless subject to interference.

A CASE STUDY: KVTI(FM)

KVTI(FM), Tacoma, Washington, is a Class C1 non-commercial FM station licensed to Clover Park TechnicalCollege. It operates with an effective radiated power of 51Kilowatts (H & V). Its antenna (a 4-bay Jampro JSCP) isside-mounted on a uniform cross-section guyed tower withits radiation center 70 meters above ground level. TheKVTI transmitter site is located in a residentialneighborhood, at the south end of the campus of Lakes HighSchool in Lakewood, Washington. There are residenceslocated within 150 feet of the base of the KVTI tower. TheKVTI 115 dBu/m blanketing contour extends 1.75 milesfrom the base of the tower.

The KVTI tower is located about 55 kilometers from theSeattle area FM and TV transmitter sites on CougarMountain, Queen Anne Hill, and Capitol Hill; about 60kilometers from the FM broadcast site on West TigerMountain; and about 46 kilometers from the Channel 13 andChannel 20 transmitter sites on Gold Mountain. Themajority of the off-the-air FM and TV signals available inLakewood are from the Seattle area transmitter sites.

The station began operating from this transmitter site in Mayof 1991. Even before going on the air, the station initiateda program designed to resolve interference complaints,using the services of a local TV-radio service shop. Sincethe station initially went on the air, more than 100complaints related to blanketing interference in the vicinityof the KVTI site have been resolved. In April of 1994, agroup of neighbors living in the vicinity of the KVTI sitefiled a petition with the FCC, complaining of blanketinginterference from KVTI.

In response to the petition, the Commission sent a letter(1800B3-MJF, dated August 22, 1994) to KVTI requiringthe station to resolve 20 “previously referred” unresolvedcomplaints and to provide “effective technical assistance” to46 new complainants whose names were listed in thepetition. The letter also required KVTI to submit a detailedreport regarding the resolution of the complaints, includingmaps showing the locations of all the affected residences.The majority of the new complainants listed in the petitionhad never contacted KVTI prior to signing the petition.

Clover Park Technical college retained Hatfield andDawson as project manager to help resolve the interferencecomplaints and to prepare the report to the FCC. Mr.

Joseph N. (Nick) Winter, Jr. of Broadcast ServicesNorthwest was also retained by the College to assist withthe field work and to carry out the station’s program ofcontinuing assistance for neighbors with interferenceproblems. The author, Mr. Winter, and Mr. StephenLockwood, P.E. of Hatfield & Dawson performed all thesite visits and equipment tests required for the project.

The blanketing interference symptoms described in thispaper and the techniques used to ameliorate them arebased on what we learned in our visits with the residentsof Lakewood.

Affected Equipment, Symptoms of BlanketingInterference, and Measures Employed to AmeliorateInterference

Described below are the types of equipment found to besusceptible to various forms of blanketing interferenceand the corrective measures which were successfully usedto ameliorate the interference:

! Television Receivers - A wide range of televisionreceivers were affected by blanketing interference,ranging from 5" portable models to 48" projection TVs.Many households had a number of affected TV’s; somehouseholds had as many as 12 affected receivers, oftenwith accompanying VCR’s. TVs connected to off the airreceiving antennas or using “rabbit ears” were usuallymost severely affected when tuned to channels 4, 5, and7. The effects of the interference ranged from very slight“fuzziness” in the picture to a “herringbone” pattern in thevideo. In the most extreme cases, the herringbone patterncompletely obliterated the picture. In some cases, audiofrom the radio station could be heard on the TV speakers.The severity of the interference depended upon the D/Uratio between the desired TV signal and the undesiredblanketing signal.

TVs connected to the cable system often exhibited similarsymptoms to those connected to off-the-air antennas,depending upon the level of the blanketing signal leakinginto the cable distribution system. In addition, TVsconnected to home cable systems used to feed multiplesets from a single CATV drop often exhibited mild tomoderate herringbone patterns on cable channels 8 and 34(corresponding to the frequency of the 2nd harmonic and3rd harmonic of the FM station). Measurements at theFM transmitter demonstrated that the signals producingthis interference were not being radiated directly by thetransmitter. This type of interference appeared to beproduced by spurious products produced in non-linearjunctions in the cable feed systems, in external metallicjunctions (power lines, phone lines, metal fences, etc.), orin the front ends of other TV receivers connected to the

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cable feed system. The only effective techniques we foundto correct these problems were to increase the level of thedesired signals on channels 8 and 32 and/or to replace thetelevision set with a model less susceptible to this type ofinterference.

In nearly all cases, the installation of a Microwave FilterCompany 5KFM-90.9 notch filter at the RF input connectorof the TV and a Fair-Rite 04433164151 “clip-on” ferritecore or a Fair-Rite 5943003801 toroid core on the ACpower cord eliminated the interference. (This techniquewas not effective for the channel 8 and channel 32interference, since it was produced by a spurious signal ona frequency far outside the range of the notch filter, andbecause the use of a notch at the channel 8 or channel 32frequencies would have eliminated the desired signals aswell.) In some cases, the interference could not beeliminated using these techniques, and the TV had to bereplaced with a new model known to be less susceptible tointerference. Most of the TV’s which had to be replacedwere older models without an “F” connector integral to thetuner module. These TV’s were usually overloaded by theFM radio frequency energy entering the tuner directlythrough the TV’s case.

Figure 3 shows the installation details for the filters andtoroid cores. Drawings similar to those in Figure 3, alongwith detailed written instructions were provided tocomplainants as part of a “handbook” prepared by our firm,which describes how to resolve common blanketinginterference problems.

! VCRs-The interference effects observed in VCR tunerswere very similar to those observed in TVs. The sameremedial measures used for TVs were successfully used forVCRs. In many cases, the VCR tuners were less susceptibleto interference and produced better picture quality than TVreceivers of the same vintage. It was not necessary toreplace any VCRs in the blanketing area.

! Home CATV Cabling - Many of the households wevisited had extensive internal cable distribution systems,often using a single feed from the cable company andmultiple splitters to feed as many as 10 TV receivers. Thisresulted in very low TV signal levels at the “downstream”end of these systems, which made the receivers connectedto the cable much more susceptible to interference from thestrong FM signal. In many cases, even replacing the cablein these systems with double-shielded coax did not reducethe level of the FM signal leaking into the system toeliminate the interference. In these cases, powered splitterswere installed to increase the level of the desired TV signalsat the downstream receivers. Notch filters were installed atthe input of the powered splitter to prevent amplifieroverload by the strong FM signal, as shown in Figure 3.

! Rooftop Antennas - In a several cases, rooftopantenna systems had to be modified to increase the levelof desired TV signals and/or to reduce the level of theinterfering FM signal entering FM and TV receivers. 300ohm twinlead downlead connections were replaced withdouble-shielded coax and splitters were added in place ofparallel-connected downleads. These modifications bothhelped to reduce the interference and improved the signalquality at the TV receivers.

! AM/FM/Shortwave Radios and Boomboxes - Thestrong FM signal did not affect the operation of theBroadcast Band AM tuners in most radios; a significantlevel of 60 Hz power line noise in the neighborhoodtended to limit the availability of AM signals to those withhigh signal strength. The FM tuners in manyboomboxes, inexpensive “all-in-one” component stereosystems, and a significant number of quite expensive FMcomponent receivers exhibited symptoms of receiverdesensitization, intermodulation, and the production ofmultiple images of the blanketing station. On mostreceivers, these effects were observed below about 93MHz on the FM band, but in some cases, the entire FMband was wiped out.

On receivers with coaxial antenna connectors, theinstallation of a notch filter usually eliminated theinterference effects. Receivers with 300 ohm twinleadantenna connectors proved to be more of a problem,though it was frequently possible to use a combination oftwo 300/75 ohm baluns and a notch filter to restore thenormal operation of the receiver with a 300 ohm twinleadantenna.

In many cases, even after the FM tuner section of asystem was restored to normal operation, the FM station’sdetected audio could still be heard in the tape playeroutput or in the power amplifier of a component system.These problems could usually be solved by the installationof ferrite cores on the AC power lead, the speaker leads,and all the audio interconnections in a component system.Figure 4, also taken from the “handbook”, shows theinstallation details for the ferrite cores. In some cases,even these measures were unsuccessful, and the receiveror compact component system had to be replaced with aunit less susceptible to interference.

Boomboxes were an especially difficult problem, sincemany models have either a telescoping monopole externalantenna or use the AC power cord as an antenna. Also,most boomboxes have plastic cases which provide little orno shielding against unwanted RF signals. In some cases,where the tuner section of the boombox functionednormally, but the tape player or the amplifier sectionsuffered from RF rectification, it was possible to restore

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normal operation by installing ferrite cores on the speakerleads and the AC power cord, as shown in Figure 4.

We encountered several boomboxes withAM/FM/Shortwave tuners (there are many retired militaryresidents of Lakewood, and these receivers had all beenimported from overseas). The shortwave sections of thesetuners were universally obliterated by the strong FM signal.These units were replaced with separate shortwave radiosand AM/FM boomboxes.

! Intercoms - These units tended to suffer mainly fromRF detection in their amplifier sections, which wasrelatively easy to eliminate by the installation of ferrite coreson the speaker and remote unit leads. One unit whichincluded an integral radio was more difficult to deal withbecause it did not have any kind of external antenna, and didnot have any obvious connection between the tuner circuitboard and the outside world. This unit required somecustom modification.

! Clock Radios - Surprisingly, some clock radiosfunctioned normally in the high ambient RF field, and othershad severe problems. Since these units all had plastic casesand most did not have external antenna connectors, the onlyavailable remedial measure for affected radios was toreplace them.

! Telephones - Although telephones are specificallyexcluded from protection under §73.318, complaints abouttelephone interference comprise the single largest categoryin blanketing interference areas. Because the telephone isused often on a daily basis, the presence of a radio station’saudio in the background on the phone is a constant irritantwhich will generate ill will in the neighborhood surroundingan FM transmitter site. In all cases we encountered it waspossible to eliminate audio rectification in telephones byinstalling filters fitted with the appropriate modularconnectors at the line cord and the handset cord of thetelephone. We used filters custom manufactured byCoilcraft. In some cases, it was also necessary to install aclip-on ferrite core on the line cord or headset cord of thephone close to the body of the phone in order to eliminatethe interference.

Some cases of telephone interference were produced by the1 kW daytime AM station which operates from atransmitter site at the north end of the Lakes High Schoolcampus. Because residents did not tend to distinguish oneform of radio interference from another, the most expedientsolution to this problem, was the installation of appropriatefilters designed to attenuate medium wave frequencies.

Most cordless telephones did not suffer from blanketinginterference. The majority of the cordless phones in the

Lakewood area were models manufactured by GE andSouthwestern Bell.

Other Sources of Interference

Several other sources of interference to radios and TVswere identified during the site visits. It is important toidentify and categorize the effects of these other sourcesbecause residents affected by blanketing interference donot have the technical background or any means ofdistinguishing various forms of interference, and tend toattribute all interference to the FM station.

! AM Radio Stations - On some AM tuners, thestrong local signal from the daytime AM station producedintermodulation products which appeared at severallocations on the dial. Turning the FM transmitter on andoff had no effect on these products.

! Power Line Noise - Some residents lived adjacent toa power utility substation in an area which was locatedbehind a small hill and was shadowed from all the Seattlearea TV transmitter sites. The 60 Hz noise level in thisneighborhood was especially severe in this neighborhood,especially after long periods with no rain increased thelevel of corona discharge across high voltage insulators inthe power distribution system. The low-band VHF TVsignals received off-the-air in this neighborhood werevery noisy; even after on/off tests were used todemonstrate that this interference was not caused by theFM station, complaints were still received about this typeof interference.

! Touch Lamps and Light Dimmers - One residencehad several “touch lamps” which used a capacitive touchswitch in the base of the lamp as an on/off switch. Whenthese lamps were turned on they produced fairly highlevel noise pulses spaced about 100-150 KHz intervalsfrom the VLF band up through 20 MHz. The noiseproduced by these lamps severely disrupted reception onmedium wave and shortwave radios, showing up as a loudbuzz at regular intervals across the operating band of thereceiver. At first, this interference appeared to beproduced by the FM station, because when a shortwaveradio was tuned to a frequency occupied by one of thenoise pulses, turning off the FM station appeared to causethe interference to go away. Further investigation using aspectrum analyzer revealed that turning the FMtransmitter on and off merely shifted the frequency of theentire noise pulse spectrum generated by the touch lamps,but that it did not affect the amplitude of the RF noisethese devices produced. With the FM transmitter turnedoff, it was possible to retune the affected receiver and tofind the interference at its new frequency.

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Figure 1 - MFC 5KFM-90.1 Filter Response

Figure 2 - RS FM Trap Frequency Response

SCR light dimmers produced a similar noise pattern, but itwas much less severe than the noise produced by the touchlamps.

Signal Measurement Procedure Used During Site Visits

At each household, detailed note sheets were made for eachpiece of equipment, and, for the majority of the households,spectrum analyzer measurements were made showing thereceived television signal strength levels and the FM signallevels provided by outdoor receiving antennas or by thelocal cable system. The signal level measurements weremade in as many cases as possible to provide data regardingthe level of television signal strength required at typicaltelevision sets to overcome the effects of interference fromthe strong FM signal. In many cases a measurement wasmade of the ambient KVTI field strength in the vicinity ofthe equipment affected by blanketing interference. Themeasured KVTI (FM) field intensity inside homes in theblanketing area ranged from 100 mV/m in houses locatedmore than a few thousand feet from the transmitter site tomore than 1 V/m in houses located immediately adjacent tothe KVTI tower.

Quality of Off-the-Air TV Signals in Lakewood

Our measurements and site visits showed that off-the-airtelevision reception in the absence of FM blanketinginterference from was adequate (though generally not whatone would call a high quality signal) in some areas ofLakewood using a pair of "rabbit ears" mounted on top ofthe TV set. In other areas, reception was sometimes poor tototally unusable, even with a rooftop antenna.

Both the measurements and the observations of the qualityof received TV signals showed that there was a verypronounced diurnal (day-to-night) variation in the strengthof both the TV and the FM signals from the Seattlebroadcast transmitter sites on Queen Anne Hill, Capitol Hill,Cougar Mountain, and West Tiger Mountain. Given thedistances between the transmitter sites and the receiverlocations, the nature of the intervening terrain, and the factthat none of the receiver locations had adequate Fresnelzone clearance from the Seattle FM and TV transmittersites, these variations were not entirely surprising.

At some locations, the change in propagation conditionsfrom mid-day (when the air near the surface was wellmixed) to early morning or late afternoon or evening (whenthe air tended to be more stratified) was significant tochange the video and audio signal quality of the TV signalsfrom good quality typical of a line-of-sight path to verynoisy and "ghosty" poor quality typical of a diffraction path.This type of variation even caused all but a few of the

available Seattle FM station signals to drop below themuting threshold of one FM receiver as day changed tonight.

Notch Filter Characteristics

Microwave Filter Company 5KFM-90.9 notch filterswere used to attenuate the KVTI signal at the input to TVand FM receivers. These filters have a 60 dB notch and a3 dB bandwidth of +/- 3 MHz, so they can be used withminimal detrimental effect on the other off-the-air FMsignals or on the Channel 6 aural carrier in cable systems.A spectrum analyzer plot of the frequency response ofthis filter is shown shown in Figure 1:

For purposes of comparison, the frequency response of aRadio Shack FM Trap (Part # 15-577), which hassometimes been used (often unsuccessfully) to attempt tomitigate blanketing interference is shown in Figure 2:

As shown in Figure 2, the Radio Shack FM trap has lessthan 15 dB of rejection relative to the 3 dB point of theMFC notch filter, while the MFC notch provides morethan 60 dB. The RS FM trap also has a relatively highinsertion loss, has nearly 10 dB of amplitude responsevariation over the band occupied by Channel 6, and tendsto degrade the quality of TV signals in low signalenvironments.

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Tests of TV and Radio Receivers

Prior to making site visits with replacement equipment, anumber of TV and radio receivers were tested at or near theKVTI transmitter site to determine which units were likelyto function well in the high level RF field environment ofthe blanketing area.

The results of the TV receiver tests are shown in Tables 1and 2. Table 1 shows the interference caused to eachreceiver when connected directly (with no filters) to a testreceiving antenna at the KVTI transmitter site. Table 2shows the reduction in interference for each receiver whichresulted from the installation of an MFC 5KFM-90.9 notchfilter between the antenna downlead and the antenna inputconnector on the TV. Based on these measurements, the bestfour out of six receivers were selected for use asreplacement TVs in households in the blanketing area.Although it is not shown in the data, a further reduction ininterference caused to some of the TVs resulted fromwinding several turns of the antenna downlead through atoroid core before connecting the downlead to the MFCfilter. This reduced the level of RF energy conducted alongthe coax cable shield, which eliminated some residualinterference effects in some cases. Even though two out ofthe six TVs had some problems at the KVTI transmitter site,we found in general that most modern TV receivers can bemade to function correctly in the blanketing environment ifappropriate filters and toroids are used and if a desiredsignal of adequate level is provided at the receiver antennainput.

Several AM/FM boomboxes and micro and mini componentstereo systems were also tested in advance of installation inhouseholds. All the radios tested had digital tuningindicators and synthesized tuners. The following units werefound to operate well in the blanketing environment:

! JVC PC-X105 AM/FM/Dual Cassette/CD

! JVC RC-QS11 AM/FM/Cassette/CD

! JVC UX-T1 AM/FM/CD/Cassette Micro ComponentSystem

! Sony MHC-450 AM/FM/CD/Cassette MicroComponent System

! Samsung SCM-8300 AM/FM/CD/Cassette MiniComponent System (with RIAA phono inputs)

The Samsung unit was used in cases where a system with aturntable needed to be replaced. Shortwave receivers werereplaced with a Grundig YB-400 “Yachtboy” portable

model. A larger and more expensive Grundig model didnot function adequately in the blanketing environment.

Establishing and Maintaining Good PublicRelations

Efforts to resolve blanketing interference complaints canbe most successful if the following general guidelines arefollowed:

! Set up a system for receiving and tracking complaintsbefore you turn on the transmitter at a new site.

! Retain experienced and competent technical help;sending out inexperienced people who do not knowhow to resolve interference problems will only causemore problems later.

! Document everything you do.

! Communicate with the neighbors; let them knowwhat you are doing to resolve their problems; followup after site visits.

! Don’t minimize your complainants problems orattempt to blame them on the equipment they areusing. Put yourself in their shoes.

! Go the extra mile; even if you are not required by theCommission’s Rules to solve every problem, themore problems you actually do solve, the more goodwill you will generate among your neighbors.

Received Signal Television Receiver Manufacturer and Model Number

Off-the AirTV

Channel

Measured TVSignal

Strength atReceiver(dBmV)

TV/FMD/URatio(dB)

Toshiba CF19C20

20 inch TV(August 1993)

JVC C-20CL5

20 inch TV(May 1994)

Hitachi20MA1B

20 inch TV(October 1993)

MitsubishCS-2010120 inch TV

(October 1993)

SamsungTTB2012

20 inch TV(April 1994)

PanasonicCF20S2S20 inch TV(June 1994)

Channel 4 -12.4 -64.6 Good quality videoand audio

Severeherringbone onvideo; audio OK


Picture completelyobliterated; audioOK

Severe herring-bone on video;audio OK

Moderate herring-bone on video;audio OK

Channel 5 -11.9 -64.1 Severe herring-bone on video;audio cuts in/out

Severe herring-bone on video; nocolor; audio OK


Picture completelyobliterated; audioOK

Severe herring-bone - no picture;audio OK

Very slight “fuzzi-ness on video;audio OK; ghosts

Channel 7 -10.8 -63.0 Excellent video &audio quality

Moderateherringbone onvideo; audio OK

Slight herringboneon video; audio OK

Severe herring-bone on video;audio OK

Slight herringboneon video; audioOK

Very slightherringbone onvideo; audio OK

Channel 9 -5.1 -57.3 Slight herring-boneon video

Severeherringbone onvideo; color on/off;audio OK

Moderateherringbone onvideo; audio OK

Severe herring-bone on video--nopicture; audio OK

Severe herring-bone - picture justvisible in noise;audio OK

Moderate herring-bone; picture atnoise level; audioOK

Channel 11 -3.0 -55.2 Excellent videoand audio quality


Excellent videoand audio quality(Ch. 12 also OK)



Very good qualityvideo and audio

Channel 13 0.0 -52.2 Excellent videoand audio quality

Slight “fuzziness”on video; audio OK

Excellent videoand audio quality


Good quality videoand audio

Excellent qualityvideo and audio

Channel 20 -8.0 -60.2 Not tested Not tested Not tested Not tested Good quality videoand audio




Excellent videoand audio quality

No signal; belowRX squelch level

Slight herringboneon video; audioOK


Channel 28 16.9 -35.3 Not tested Not tested Not tested Not tested Very good qualityvideo and audio


KVTI(90.9 MHz)

52.2 N/A N/A N/A N/A N/A N/A N/A

Table 1 - FM Interference to Representative TV Receivers (Direct Connection to Receiving Antenna)


Off-the AirTVChannel

Measured TVSignal

Strength atReceiver(dBmV)

TV/FMD/URatio(dB)

Toshiba CF19C20

20 inch TV(August 1993)

JVC C-20CL5


Hitachi20MA1B


MitsubishiCS-2010120 inch TV

(October 1993)

SamsungTTB2012



Channel 4 -12.4 -3.0 Good quality videoand audio; somenoise on video

Noisy signal; nodifference with FMon or off

Good quality videoand audio; justperceptible changewith FM on

Good quality audioand video;“fuzziness” onvideo; audio OK




Very high qualityvideo and audio

Very slight“fuzziness” in video









Very slight “fuzzi-ness” on video;audio OK

Channel 9 -5.1 4.3 Excellent videoand audio quality

Slight herringbonein video; audio OK



Very slight herring-bone on video;audio OK



Slight “fuzziness”in video; enteringset through case


Very slight herring-bone in video;audio OK



Channel 13 0.0 9.4 Excellent videoand audio quality

Slight “fuzziness”in video; enteringset through case


Very slight herring-bone in video;audio OK



Channel 20 -8.0 1.4 Not tested Not tested Not tested Not tested Very good qualityvideo and audio



Slight “fuzziness”on video; enteringset through case





Channel 28 16.9 26.3 Not tested Not tested Not tested Not tested Excellent qualityvideo and audio


KVTI(90.9 MHz)

-9.4 (withMFC notch

filter)

N/A N/A N/A N/A N/A N/A N/A

Table 2- FM Interference to Representative TV Receivers (MFC 5KFM-90.9 Notch Filter)


Off-the AirTV Channel

MeasuredTV SignalStrength atReceiver(dBmV)

TV/FMD/URatio(dB)

Toshiba CF19C20 20 inch TV

(August 1993)

JVC C-20CL5


Hitachi20MA1B


MitsubishCS-2010120 inch TV

(October 1993)

SamsungTTB2012



Channel 4 -12.4 -3.0 Good quality videoand audio; somenoise on video

Noisy signal; nodifference with FMon or off

Good quality videoand audio; justperceptible changewith FM on

Good quality audioand video; slight“fuzziness” onvideo; audio OK

Slight herring-boneon video; audio OK

Slight “fuzziness”in video; audio OK


Very high qualityvideo and audio




Very slight“fuzziness” invideo; audio OK














Very slight“fuzziness” invideo; entering setthrough case





Channel 13 0.0 9.4 Excellent videoand audio quality






Channel 20 -8.0 1.4 Not tested Not tested No tested Not tested Very good qualityvideo and audio








Channel 28 16.9 26.3 Not tested Not tested Not tested Not tested Excellent qualityvideo and audio


KVTI(90.9 MHz)

-9.4 (withMFC filterand torroid

core)

N/A N/A N/A N/A N/A N/A N/A

Table 3 - FM Interference to Representative TV Receivers (5KFM-90.9 Notch Filter & Fair-Rite 5943003801 Ferrite Core)

FM Blanketing Interference

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