Bob Lehman Regional Trainer

1
Welcome

• Bob Lehman Regional
  Trainer
• Bright House Networks Tampa Bay
  Division Tri County
  Region

2
AM RFI and Digital Phone Services

• AM RFI Definition
• Subscriber Symptoms
• What Didnt Work
• What Did Work
• Subscriber Success Stories
• Recommendations

3
Definition

• RFI-Radio Frequency Interference Any
  undesirable electrical energy with content within
  those ranges dedicated to RF transmission. Most
  often found in the low frequency range of several
  kHz to 30MHz.
• In other wordsThe reception of a radio or
  television signal on a device not normally
  expected to receive it.

4
Telephone RFI

• Telephone RFI is the demodulation of radio
  signals by telephones.
• When strong RF carriers are present, wires
  connected to telephones can act as an antenna,
  they invite the flow of RF current. This current
  goes directly into the telephone where
  demodulation can combine the interference audio
  with the desired telephone audio.

5
AM Tower Considerations

• Phone equipment within ½ mile of a 5kW AM tower
  is susceptible to RFI. As a result extra care
  must be taken with all cabling and connections.
• Phone equipment closer then ¼ mile to a 5kW
  transmitter will often require some type of RFI
  filtering.

6
Subscriber Symptoms From AM Tower RFI

• RFI may be light background noise.
• RFI may be loud audio that is so heavy it makes
  the service unusable.
• RFI severity often changes between daytime and
  nighttime hours.
• RFI severity often changes with atmospheric
  conditions.
• Persons calling the subscriber may or may not
  also hear the RFI.

7
Tracking the AM Tower RFI

• Connecting a Test MTA at the tap, amplifier
  then node had little effect.
• Connecting to nearby taps in adjacent nodes had
  little effect.
• Moving farther then ½ mile from the transmission
  tower was the only thing that completely removed
  the RFI.

8
Isolating the MTA Near AM Tower

• The grounding at the power meter only removes a
  portion of the RFI.
• Isolating the MTA from the coaxial outer
  conductor had some impact but did not resolve the
  issue.
• Adding external shielding to the MTA is difficult
  because of the coaxial cables outer conductor.

9
Solutions for AM Tower RFI

• 1. Eliminate unused/damaged wiring
• 2. Use the filtering already in the NID
• 3. Introduce better filtering in the NID
• 4. Add modular filtering at the MTA
• 5. Add modular filtering at phones

10
Charles Severe Service 12-15D 29.00
11
Opto-Tech SA-150 16.00
Model SA-150
Attenuation (dB)
0
-10
-20
-30
-40
-50
-60
-70
-80
50 kHz
100 kHz
400 kHz
5 MHz
200 MHz
12
Allen Tel AT100 6.00
13
Opto-Tech M-150 27.00
14
W Lake Bonny Dr. Success Story

• Address is situated about 500 from WLKFs tower.
• WLKF AM 1430khz -- 5.0 kW day WLKF AM 1430khz
  -- 1.0 kW night
• Subscriber complained of heavy RFI occurring
  during the day then lighter at night.
• Technician found RFI present when telephone was
  connected directly to MTA

15
WLKF
16
W Lake Bonny Dr. Success Story

• Partial RFI elimination was achieved by placing
  an in-line filter in the NID.
• The remainder of the RFI was removed with a
  modular filter at one phone jack.
• Remember to route the MTAs dial tone through the
  NID first then to the phones when using an
  in-line filter.

17
W Lake Bonny Dr. Success Story
18
N Roscoe Rd. Success Story

• Address is situated about 350 from WRZNs tower.
• WRZN AM 720khz - 10.0 kW day WRZN AM 720khz -
  .25 kW night
• Subscriber complained of heavy RFI symptoms
  occurring during the day.
• Technician found RFI. It was not fully
  correctable with one in-line filter.

19
WRZN
20
N Roscoe Rd. Success Story

• Partial RFI elimination was achieved by placing
  an in-line filter in the NID.
• Partial RFI elimination was achieved by placing a
  modular filter at the MTA.
• The remainder of the RFI was removed by a modular
  filter at each phone jack.

21
N Roscoe Rd. Success Story
modular
In-Line
Single Wall Plates
NID
modular
Dual Wall Plate
modular
modular
MTA
22
More RFI Protection

• Type of Telephone- RFI may have a greater effect
  on some telephones than others. This may be due
  to differences in telephone design or location.
• Type of Cabling- Shielded twisted pair (STP) or
  Screened twisted pair (ScTP) is suitable for
  environments susceptible to RFI.

23
The Exception to the Rule

• Audible RFI noise may also be created within a
  telephone. Circuits and certain components within
  a telephone can act as both antenna and receiver
  for any RF emissions in a given area.

24
Recommendations

• Find RFI prone areas before they find you with
  www.fcc.gov/mb/audio/amq.html.
• Use City and State or Call letters to find tower
  locations and transmitter power.
• Inform installers/technicians about these areas
  and how to deal with them.
• Equip installers/techs with adequate filters.

25
Polk County AM Towers
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Thank You!